Download Solid phase extraction of trace elements

Spectrochimica Acta Part B 58 (2003) 1177–1233
Review
Solid phase extraction of trace elements
´ Camel*
Valerie
Institut National Agronomique Paris-Grignon, Analytical Chemistry Laboratory, 16 Rue Claude Bernard,
Paris Cedex 05 75231, France
Received 2 December 2002; accepted 26 March 2003
Abbreviations: AAS, Atomic absorption spectrometry; ACN, Acetonitrile; AES, Atomic emission spectrometry; APDC,
Ammonium pyrrolidine dithiocarbamate; BAS, Biswl-hydroxy-9,10-anthraquinone-2-methylxsulfide; 5-BrPADAP 2-(5-bromo-2pyridylazo)-5-diethylaminophenol; BSQ, 8-(Benzenesulfonamido)quinoline; 18C6, 18-Crown-6; CA, Chromotropic acid; CTA,
Cetyltrimethylammonium; CV-AAS, Cold vapour atomic absorption spectrometry; DAD, Diode array detector; DDQ, 7-Dodecenyl8-quinolinol; DDTC, Diethyldithiocarbamate; DDTP, 0,0-Diethyl-dithiophosphate; DEBT, N,N9-Diethyl-N9-benzoylthiourea; DESe,
Diethyl selenide; DMBS, Dimethylglyoxal bis(4-phenyl-3-thiosemicarbazone); DMDSe, Dimethyl diselenide; DMG, Dimethylglyoxime; DMSe, Dimethyl selenide; DPC, Diphenylcarbazide; DPCO, Diphenylcarbazone; DPD, N,N-Dimethyl-p-phenylenediamine;
DPTH, l,5-bis(di-2-pyridyl) methylene dithiocarbohydrazide; DVB-VP, Divinylbenzene-vinylpyrrolidone; DZ, Dithizone; DzS,
Dithizone sulfonic acid; ECD, Electron capture detection; EDTA, Ethylene diamine tetraacetic acid; ERT, Eriochrome black-T; ETAAS, Electrothermal atomic absorption spectrometry; Et, Ethyl; EtOH, Ethanol; F-AAS, Flame atomic absorption spectrometry;
FI, Flow injection; FPD, Flame photometric detection; FZ, Ferrozine; GC, Gas chromatography; GCB, Graphitized carbon black;
HDEHP, Bis(2-ethylhexyl) hydrogen phosphate; HMDC, Hexamethylenedithiocarbamate; H2 MEHP, 2-Ethylhexyl dihydrogen
phosphate; 8-HQ, 8-Hydroxyquinoline; 8-HQ-5-SA, 8-Hydroxyquinoline-5-sulfonic acid; HT18C6, Hexathia-18-crown-6;
HT18C6TO, Hexathia-18-crown-6-tetraone; IBMK, Isobutyl methyl ketone; ICP, Inductively coupled plasma; IDA, Iminodiacetate;
IP, Ion-pair; KR, Knotted reactor; LC, Liquid chromatography; LLE, Liquid–liquid extraction; LOD, Limit of detection; MBT, 2Mercaptobenzothiazole; Me, Methyl; MeOH, Methanol; MPSP, 3-Methyl-l-phenyl-4-stearoyl-5-pyrazolone; MPT, Microwave plasma
torch; MS, Mass spectrometry; NCH, Neocuproine; NDSA, 2-Naphthol-3,6-disulfonic acid; NN, 1-Nitroso-2-naphthol; ODETA, 4(N-octyl)diethylenetriamine; PA, Polyacrylate; PAA, Piconilic acid amide; PADMAP 2-(2-pyridylazo)-5-dimethylaminophenol;
PAN, 1-(2-pyridylazo)2-naphthol; PaPhA, Poly(aminophosphonic acid); PAR, 4-(2-pyridylazo)resorcinol; PC, Pyrocatechol;
PDATA, Propylenediaminetetraacetic acid; PDT, 3-(2-Pyridyl)-5,6-diphenyl-l,2,4-triazine; PDTC, Poly(dithiocarbamate); PE,
Polyethylene; PGC, Porous graphitized carbon; Ph, Phenyl; PipDTC, Piperidine dithiocarbamate; PS-DVB, Polystyrene-divinylbenzene; PTFE, Polytetrafluoroethylene; PUF, Polyurethane foam; PV, Pyrocatechol violet; ROMP, Ring-opening metathesis polymerisation; SA, Salicylic acid; SDS, Sodium dodecylsulfate; SFE, Supercritical fluid extraction; SGBM, Silica gel bound macrocycles;
SPE, Solid phase extraction; SPS, Solid-phase spectrophotometry; TAN, 1-(2-tiazolylazo)-2-naphthol; TBP, Tri-n-butyl phosphate;
T4BPP, Tetra-(4-bromophenyl)-porphyrin; TBT, Tributyltin; TCPP, Carboxyphenylporphyrin; THF, Tetrahydrofuran; TOPO, Tri-noctylphosphine oxide; TPhT, Triphenyltin; TS, Methylthiosalicylate; TSA, Thiosalicylic acid; TTA, 2-Thenoyltrifluoroacetone; UV,
Ultraviolet; XO, Xylenol orange.
*Corresponding author. Tel.: q33-1-44-08-17-25; fax: q33-1-44-08-16-53.
E-mail address: [email protected] (V. Camel).
0584-8547/03/$ - see front matter 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0584-8547Ž03.00072-7
1178
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
1. Introduction
Despite the selectivity and sensitivity of analytical techniques such as atomic absorption spectrometry, there is a crucial need for the
preconcentration of trace elements before their
analysis due to their frequent low concentrations
in numerous samples (especially water samples).
Additionally, since high levels of non-toxic components usually accompany analytes, a clean-up
step is often required. Liquid–liquid extraction is
a classical method for preconcentrating metal ions
andyor matrix removal. Solid phase extraction
(SPE) is another approach that offers a number of
important benefits. It reduces solvent usage and
exposure, disposal costs and extraction time for
sample preparation. Consequently, in recent years
SPE has been successfully used for the separation
and sensitive determination of metal ions, mainly
in water samples. After outlining the theory of this
technique, guidelines are given for the development of SPE-based methods for preconcentration
of many trace elements. Finally, examples of applications are presented.
2. Theory
The principle of SPE is similar to that of liquid–
liquid extraction (LLE), involving a partitioning
of solutes between two phases. However, instead
of two immiscible liquid phases, as in LLE, SPE
involves partitioning between a liquid (sample
matrix) and a solid (sorbent) phase. This sample
treatment technique enables the concentration and
purification of analytes from solution by sorption
on a solid sorbent. The basic approach involves
passing the liquid sample through a column, a
cartridge, a tube or a disk containing an adsorbent
that retains the analytes. After all of the sample
has been passed through the sorbent, retained
analytes are subsequently recovered upon elution
with an appropriate solvent. The first experimental
applications of SPE started fifty years ago w1,2x.
However, its growing development as an alternative approach to liquid–liquid extraction for sample preparation started only in the mid-1970s. It
has been extensively used in the past fifteen years
for the preconcentration of organic micropollu-
tants, especially pesticides, in water samples w3x.
However, numerous studies have also shown the
great potential of this technique for speciation
studies.
2.1. Presentation of the technique
2.1.1. Basic principles
An SPE method always consists of three to four
successive steps, as illustrated in Fig. 1. First, the
solid sorbent should be conditioned using an
appropriate solvent, followed by the same solvent
as the sample solvent. This step is crucial, as it
enables the wetting of the packing material and
the solvation of the functional groups. In addition,
it removes possible impurities initially contained
in the sorbent or the packaging. Also, this step
removes the air present in the column and fills the
void volume with solvent. The nature of the
conditioning solvent depends on the nature of the
solid sorbent. Typically, for reversed phase sorbent
(such as octadecyl-bonded
{
silica), methanol is
frequently used, followed with water or aqueous
buffer whose pH and ionic strength are similar to
that of the sample. Care must be taken not to
allow the solid sorbent to dry between the conditioning and the sample treatment steps, otherwise
the analytes will not be efficiently retained and
poor recoveries will be obtained. If the sorbent
dries for more than several minutes, it must be
reconditioned.
The second step is the percolation of the sample
through the solid sorbent. Depending on the system
used, volumes can range from 1 ml to 1 l. The
sample may be applied to the column by gravity,
pumping, aspirated by vacuum or by an automated
system. The sample flow-rate through the sorbent
should be low enough to enable efficient retention
of the analytes, and high enough to avoid excessive
duration. During this step, the analytes are concentrated on the sorbent. Even though matrix components may also be retained by the solid sorbent,
some of them pass through, thus enabling some
purification (matrix separation) of the sample.
The third step (which is optional) may be the
washing of the solid sorbent with an appropriate
solvent, having a low elution strength, to eliminate
matrix components that have been retained by the
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
1179
Fig. 1. SPE operation steps.
solid sorbent, without displacing the analytes. A
drying step may also be advisable, especially for
aqueous matrices, to remove traces of water from
the solid sorbent. This will eliminate the presence
of water in the final extract, which, in some cases,
may hinder the subsequent concentration of the
extract andyor the analysis.
The final step consists in the elution of the
analytes of interest by an appropriate solvent,
without removing retained matrix components. The
solvent volume should be adjusted so that quantitative recovery of the analytes is achieved with
subsequent low dilution. In addition, the flow-rate
should be correctly adjusted to ensure efficient
elution. It is often recommended that the solvent
volume be fractionated into two aliquots, and
before the elution to let the solvent soak the solid
sorbent.
2.1.2. Retention of trace elements on the sorbent
Adsorption of trace elements on the solid sorbent is required for preconcentration (see Fig. 2).
The mechanism of retention depends on the nature
of the sorbent, and may include simple adsorption,
chelation or ion-exchange. Also, for trace elements, ion-pair solid phase extraction may be used.
2.1.2.1. Adsorption. Trace elements are usually
adsorbed on solid phases through van der Waals
forces or hydrophobic interaction. Hydrophobic
interaction occurs when the solid sorbent is highly
non-polar (reversed phase). The most common
sorbent of this type is octadecyl-bonded silica
(C18-silica). More recently, reversed polymeric
phases have appeared, especially the styrene-divinylbenzene copolymer that provides additional pp interaction when p-electrons are present in the
analyte w4x. Elution is usually performed with
organic solvents, such as methanol or acetonitrile.
Such interactions are usually preferred with online systems, as they are not too strong and thus
they can be rapidly disrupted. However, because
most trace element species are ionic, they will not
be retained by such sorbents.
2.1.2.2. Chelation. Several functional group atoms
are capable of chelating trace elements. The atoms
most frequently used are nitrogen (e.g. N present
in amines, azo groups, amides, nitriles), oxygen
(e.g. O present in carboxylic, hydroxyl, phenolic,
ether, carbonyl, phosphoryl groups) and sulfur
(e.g. S present in thiols, thiocarbamates, thioethers). The nature of the functional group will give
an idea of the selectivity of the ligand towards
1180
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
trace elements. In practice, inorganic cations may
be divided into 3 groups:
– group I-‘hard’ cations: these preferentially react
via electrostatic interactions (due to a gain in
entropy caused by changes in orientation of
hydration water molecules); this group includes
alkaline and alkaline-earth metals (Ca2q,
Mg2q, Na2q) that form rather weak outer-sphere
complexes with only hard oxygen ligands.
– group II-‘borderline’ cations: these have an
intermediate character; this group contains
Fe2q, Co2q Ni2q Cu2q Zn2q Pb2q Mn2q. They
possess affinity for both hard and soft ligands.
– group III-‘soft’ cations: these tend to form
covalent bonds. Hence, Cd2qand Hg2q possess
strong affinity for intermediate (N) and soft (S)
ligands.
Fig. 2. Interactions occurring at the surface of the solid sorbent.
F, functional group; TE, trace element; MS, matrix solvent; MI,
matrix ions; ES, elution solvent.
For soft metals, the following order of donor
atom affinity is observed: 0-N-S. A reversed
order is observed for hard cations. For a bidentate
ligand, affinity for a soft metal increases with the
overall softness of the donor atoms: (0, 0)-(0,
N)-(N, N)-(N, S). The order is reversed for
hard metals. In general, the competition for a given
ligand essentially involves Group I and Group II
metals for O sites, and metals of Group II and
Group III for N and S sites. The competition
between metals of Group I and Group III is weak.
Chelating agents may be directly added to the
sample for chelating trace elements, the chelates
being further retained on an appropriate sorbent.
An alternative is to introduce the functional chelating group into the sorbent. For that purpose,
three different means are available: (1) the synthesis of new sorbents containing such groups (new
sorbents); (2) the chemical bonding of such
groups on existing sorbents (functionalized sorbents); and (3) the physical binding of the groups
on the sorbent by impregnating the solid matrix
with a solution containing the chelating ligand
(impregnated, coated or loaded sorbents). The
latter remains the most simple to be used in
practice. Its main drawback is the possible flush
of the chelating agent out of the solid sorbent
during sample percolation or elution that reduces
the lifetime of the impregnated sorbent.
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Different ligands immobilized on a variety of
solid matrices have been successfully used for the
preconcentration, separation and determination of
trace metal ions. Chelating agents with an hydrophobic group are retained on hydrophobic sorbents
(such as C18-silica). Similarly, ion-exchange resins
are treated with chelating agents containing an ionexchange group, such as a sulfonic acid derivative
of dithizone (i.e. diphenylthiocarbazone) (DzS),
5-sulfo-8-quinolinol, 5-sulfosalicylic acid, thiosalicylic acid, chromotropic acid, or carboxyphenylporphyrin (TCPP) w5–8x.
Binding of metal ions to the chelate functionality
is dependent on several factors: (1) nature, charge
and size of the metal ion; (2) nature of the donor
atoms present in the ligand; (3) buffering conditions which favor certain metal extraction and
binding to active donor or groups; and (4) nature
of the solid support (e.g. degree of cross-linkage
for a polymer). In some cases, the behavior of
immobilized chelating sorbents towards metal preconcentration may be predicted using the known
values of the formation constants of the metals
with the investigated chelating agent w9x. However,
the presence of the solid sorbent may also have an
effect and lead to the formation of a complex with
a different stoichiometry than the one observed in
a homogeneous reaction w10,11x. In fact, several
characteristics of the sorbent should be taken into
account, namely the number of active groups
available in the resin phase w7,10x, the length of
the spacer arm between the resin and the bound
ligand w12x, and the pore dimensions of the resin
w13x.
2.1.2.3. Ion-pairing. When a non-polar sorbent is
to be used, an ion-pair reagent (IP) can be added
to the sorbent w14x. Such reagents contain a nonpolar portion (such as a long aliphatic hydrocarbonated chain) and a polar portion (such as an
acid or a base). Typical ion-pair reagents are
quaternary ammonium salts and sodium dodecylsulfate (SDS) w15,16x. The non-polar portion interacts with the reversed-phase non-polar sorbent,
while the polar portion forms an ion-pair with the
ionic species present in the matrix (that could be
either free metallic species in solution or
complexes).
1181
2.1.2.4. Ion exchange. Ion-exchange sorbents usually contain cationic or anionic functional groups
that can exchange the associated couter-ion. Strong
and weak sites refer to the fact that strong sites
are always present as ion-exchange sites at any
pH, while weak sites are only ion-exchange sites
at pH values greater or less than the pKa. Strong
sites are sulfonic acid groups (cation-exchange)
and quaternary amines (anion-exchange), while
weak sites consist of carboxylic acid groups (cation-exchange) or primary, secondary and tertiary
amines (anion-exchange). These groups can be
chemically bound to silica gel or polymers (usually
a styrene-divinylbenzene copolymer), the latter
allowing a wider pH range.
An ion-exchanger may be characterized by its
capacity, resulting from the effective number of
functional active groups per unit of mass of the
material. The theoretical value depends upon the
nature of the material and the form of the resin.
However, in the column operation mode, the operational capacity is usually lower than the theoretical one, as it depends on several experimental
factors, such as flow-rate, temperature, particle
size and concentration of the feed solution. As a
matter of fact, retention on ion-exchangers depends
on the distribution ratio of the ion on the resin,
the stability constants of the complexes in solution,
the exchange kinetics and the presence of other
competing ions. Even though ion-exchangers
recover hydrated ions, charged complexes and ions
complexed by labile ligands, they are of limited
use in practice for preconcentration of trace elements due to their lack of selectivity and their
retention of major ions w17x. Yet, for some particular applications they may be a valuable tool.
Hence, iron speciation was possible through selective retention of the negative Fe(III)-ferron complex on an anion-exchanger w18x. Selenium
speciation was also feasible by selectively eluting
Se(IV) and Se(VI) retained on a anion-exchanger
w19x.
2.1.3. Elution of trace elements from the sorbent
The same kind of interactions usually occur
during the elution step. This time, the type of
solvent must be correctly chosen to ensure stronger
affinity of the trace element for the solvent, to
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
1182
Fig. 3. Disposable sorbent containers.
ensure disruption of its interaction with the sorbent
(as illustrated in Fig. 2). Thus, if retention on the
sorbent is due to chelation, the solvent could
contain a chelating reagent that rapidly forms a
stronger complex with the trace metal. Elution
may also be achieved using an acid that will
disrupt the chelate and displace the free trace
element. Similarly, if retention is due to ion
exchange, its pH dependence enables the use of
eluents with different pH to be used, such as acids.
Of prime importance is to selectively elute only
the target species. So, if they are more strongly
retained on the sorbent than the interferent compounds, a washing step with a solvent of moderate
elution strength is highly advisable before elution
of the target species with the appropriate solvent.
2.2. Operation
The sorbent may be packaged in different formats: filled micro-columns, cartridges, syringe barrels and discs w2,20,21x. The disposable sorbent
containers are illustrated in Fig. 3.
2.2.1. Micro-columns
The use of a micro-column is a common procedure for extraction of trace elements from various samples. It affords the opportunity of packing
the column with the desired sorbent, so that a
broader choice than the commercially disposable
containers is available. In addition, the size of the
column (i.e. the sorbent weight) may be adapted
to the sample volume. In particular, it allows larger
sample volumes, thus enabling the preconcentration of metal ions at very low concentration levels.
However, such columns must be reused, so that
careful blank washings should be conducted to
avoid cross-contamination. In addition, columns
with a narrow internal diameter limit usable flowrates to a range 1–10 mlymin that necessitates
long trace-enrichment times for large sample volumes w22x.
As will be discussed later, micro-columns are
frequently used in systems affording the on-line
coupling of SPE to analytical techniques. However,
in that case, the size of the column is limited to
achieve acceptable analytical performance.
2.2.2. Disposable cartridges and syringe barrels
Nowadays, the most frequently used design in
off-line SPE is the cartridge or the syringe barrel.
They are usually made of polypropylene or polyethylene and filled with packing material having
different functional groups. The solid sorbent is
contained between two 20 mm polypropylene frits
(in some cases they may be made of glass). They
afford great selectivity due to the broad types of
sorbents contained in commercially available systems with different column volume available. In
addition, their disposable character prevents possible cross contamination.
Cartridges vary from as little as 100 mg to 1 g
or more. Syringe barrels range in size from 1 to
25 ml and packing weights from 50 mg to 10 g.
Solvent reservoirs may be used at the top of the
syringe barrels to increase the total volume (50–
100 ml). The barrel of the syringe terminates in a
male Luer tip, which is the standard fitting to be
used with various SPE vacuum manifolds available. For cartridges, both a female and male Luer
tips are present, to enable use of either a positive
or negative pressure.
The major disadvantages of cartridges and
syringe barrels are slow sample-processing rates
and a low tolerance to blockage by particles and
adsorbed matrix components, due to their small
cross-sectional area. Channeling reduces the capacity of the cartridge to retain analytes and results
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
in contamination of the isolated analytes with
impurities originating from the manufacturing and
packing process. Such contaminants were evident
for C18-silica cartridges, while less contaminants
were observed with C18-silica disks w23,24x.
2.2.3. Disks
The use of flat disks with a high cross-sectional
area may largely prevent all the problems encountered with columns, cartridges and tubes w21x. The
packing material is usually embedded in an inert
matrix of polytetrafluoroethylene (PTFE) microfibrils, with a typical composition of 90% wyw
sorbent and 10% wyw PTFE fibers w25x. Other
types of disks use a glass-fibre matrix to hold the
sorbent particles, in order to enable a higher flowrate. The disks are available in different diameters
from 4 to 90 mm, the size most frequently used
being 47 mm. They are designed to be used in
conjunction with a filtration apparatus connected
to a water aspirator w25x. In order to remove
potential interferences and to ensure optimal
extraction of the analyte of interest, disk cleaning
and conditioning should be done before its use.
Due to a lower void volume and a higher surface
area associated with small particles as compared
to cartridges, partitioning of the analytes is
favored. Hence, a smaller mass of sorbent is
required to process a similar volume of sample.
Disks thus present the advantage of reducing solvent volumes for both the conditioning and elution
steps. Additionally, the decreased back-pressure
encountered with these devices enables the use of
high flow-rates, and their wide bed minimizes the
chance of plugging. In addition, new technology
for embedding the stationary phase prevents channeling and improves mass transfer. As classical
disks are dedicated to the SPE of large-volume
samples, new systems have very recently emerged
that enable the use of disks for small-volume
samples: the extraction disk cartridge (the disk is
placed in a syringe-barrel format), and the 96-well
microtiter plate configuration w20,21,26x. Such systems are primarily dedicated to biological samples.
One of the drawbacks of using disks is the
decrease in the breakthrough volume (which is the
volume that can be percolated without analyte
losses). In addition, disks have lower capacity than
1183
cartridges, so that for real samples (e.g. high
content of natural organic matter in river water)
incomplete retention of the target metal species
may result w27x. As a consequence, disks are
recommended when there is a strong interaction
between the analyte and the sorbent.
2.3. Advantages of the technique
Classical liquid–liquid extractions of trace elements are usually time-consuming and labor-intensive. In addition, they require strict control of
extraction conditions, such as temperature, pH and
ionic strength. For all these reasons, several procedures tend to be replaced by SPE methods. This
technique is attractive as it reduces consumption
of and exposure to solvents, their disposal costs
and extraction time w28x. It also allows the achievement of high recoveries w29x, along with possible
elevated enrichment factors. However, as different
results between synthetic and real samples may be
observed w30x, recoveries should be estimated in
both cases as far as possible. In addition, SPE can
be interfaced on-line with analytical techniques,
such as liquid chromatography (LC) or atomic
absorption spectrometry (AAS). Its application for
preconcentration of trace metals from different
samples is also very convenient due to sorption of
target species on the solid surface in a more stable
chemical form than in solution. Finally, SPE
affords a broader range of applications than LLE
due to the large choice of solid sorbents.
2.3.1. Preconcentration
LLE requires the use of large volumes of highpurity solvent, thereby affording limited preconcentration factors. The use of SPE enables the
simultaneous preconcentration of trace elements
and removal of interferences, and reduces the
usage of organic solvents that are often toxic and
may cause contamination. Upon elution of the
retained compounds by a volume smaller than the
sample volume, concentration of the extract can
be easily achieved. Hence, concentration factors
of up to 1000 may be attained.
2.3.2. Preservation and storage of the species
SPE allows on-site pre-treatment, followed by
simple storage and transportation of the pre-treated
1184
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
samples with stability of the retained metallic
species for several days w21,24,31,32x. This point
is crucial for the determination of trace elements,
as the transport of the sample to the laboratory
and its storage until analysis may induce problems,
especially changes in the speciation. In addition,
the space occupied by the solid sorbents is minimal
and avoids storage of bulky containers and the
manpower required to handle them.
2.3.3. High selectivity
SPE offers the opportunity of selectively extracting and preconcentrating only the trace elements
of interest, thereby avoiding the presence of major
ions. This is crucial in some cases, such as with
spectrophotometric detection, since the determination of heavy metals in surface waters may necessitate the removal of non-toxic metals, such as Fe
or Zn, when they occur at high concentrations
w33x. It may also be possible to selectively retain
some particular species of a metal, thereby enabling speciation. For example, salen I modified
C18-silica is quite selective towards Cu(II) w34x,
while chemical binding of formylsalicylic acid on
amino-silica gel affords selectivity towards Fe(III)
w35x. This high selectivity may also be used to
remove substances present in the sample that may
hinder metal determination, such as lipid substances in the case of biological samples w36x.
2.3.4. Automation and possible on-line coupling to
analysis techniques
SPE can be easily automated, and several commercially available systems have been recently
reviewed w26x. Home-made systems have also been
reported w37x. In addition, SPE can be coupled online to analysis techniques. On-line procedures
avoid sample manipulation between preconcentration and analysis steps, so that analyte losses and
risk of contamination are minimized, allowing
higher reproducibility w38x. In addition, all the
sample volume is further analyzed, which enables
smaller sample volume to be used. However, in
the case of complex samples, off-line SPE should
be preferred due to its greater flexibility, and the
opportunity to analyze the same extract using
various techniques.
2.3.4.1. On-line coupling to liquid chromatography. On-line systems mainly use a micro-column.
The sorbent is chosen not only for its efficiency
in trapping analytes, but also for its compatibility
with the stationary phase packed into the chromatographic column. Indeed, it is highly recommended to use the same packing in the precolumn and
the chromatographic column to prevent losses in
efficacy upon analysis. For the case of two different sorbents being used, the retention of the analytes in the precolumn should be lower than in the
analytical column to ensure band refocusing at the
head of the chromatographic column. On-line systems with several detectors have been reported,
such as ultraviolet (UV) detector w39x or inductively coupled plasma mass spectrometer (ICP–
MS) w40x, with detection limits in the 0.05–50
mgyl range. Detection limits as low as 0.5 ngyl
could even be achieved by detection at the maximum absorption wavelength using a photodiode
array UV detector w41x. Additional coupling may
be feasible, such as the on-line coupling of supercritical fluid extraction (SFE) with an on-line
SPE–LC system w42x. The coupling of SPE to LC
via flow injection has also been reported using
cold vapour AAS (CV-AAS) as the detection,
enabling enrichment factors approximately 850
w43x.
2.3.4.2. On-line coupling to atomic absorption
spectrometry. Olsen et al. w44x and Fang et al.
w45,46x were the first to describe an on-line flowinjection (FI) sorbent extraction preconcentration
system for flame AAS (F-AAS) using microcolumns packed with a cation-exchanger. Later,
they also proposed a system for on-line flowinjection sorbent extraction preconcentration with
electrothermal vaporization AAS (ET-AAS) using
lead as a model trace element w47x. Since then,
numerous papers reported FI with on-line preconcentration followed by AAS, as exemplified by
determination of Cu, Cr(VI) or Pb w48–50x.
Selected applications are reported in Table 1. The
sorbent should provide for rapid sorption and
desorption of the analytes to be used in FI systems
w65x. In addition, it should be provided for a high
selectivity. In practice, C18-silica is very frequently
used as organic solvents (such as methanol) can
Table 1
Applications of SPE to FI on-line preconcentration systems
Matrix
Trace
elements
Inorganic sorbents
Sea and waste
Cd
waters
Eluent
Analysis method Recovery
(%)
Loading
time
(volume)
Preconcentration LOD
factor
(ngyl)
Sampling Ref.
frequency
(hy1)
None
HNO3 –
HCl
ICP–AES
97.5–104
1 min
86
1100
40
w51x
Thiourea ICP–AES
2.5% in
HNO3
HCl
Spectrophotometry
95.2–
103.3
2 min
62
4300
24
w51x
106.3
2 min
—
0.016 nM
—
w52x
Thiourea F-AAS
93.5–101
1 min
—
660
60
w53x
DPTHfunctionalizedSiO2
TSfunctionalizedSiO2
8-HQfunctionalizedSiO2
MBTfunctionalizedSiO2
Sea and waste
waters
Cd
None
Sea waters
Fe
None
Geological
sample, Cu
metal, Pb
nitrate
Certified ore
samples,
Ni alloy,
anode slime,
electrolytic
solution
Fish, human
urine
Ag
None
Ag, Au,
Pd
None
AmidinothioureidoSiO2
Thiourea F-AAS
98.7–101.4 1 min
(4.5 ml)
—
1100–17 000 —
w54x
MeHg,
EtHg,
PhHg,
Hg(II)
MeHg,
Hg(II)
Cu, Cd
APDC
C18-silica
MeOHACNwater
LC–CV-AAS
92–106
20 min
(58.5 ml)
750–950
5.5–10.4
2.3
w43x
DDTC
C18-silica
EtOH
CV-AAS
85–107.5
(25 ml)
500
16
—
w55x
APDC
C18-silica
MeOH
ET-AAS
6.5–1.26
—
w56x
EtOH
F-AAS
104 s
(0.5 ml)
30 s
25–100
C18-silica
86.7–
106.5
88.9–
100.5
22–32
300–6000
90
w57x
MeOH
ET-AAS
82.5–
111.2
110 s
(0.5 ml)
25–50
1.7–4
9–12
w58x
Sea water
Certified sea
waters
Certified sea
water,
mussel,
geological
samples
Certified
sea waters
Cu, Cd, Co 1,10Phenanthroline
Cd
C18-silica
PAR or
PADMAP
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Chelating Sorbent
agent
added
1185
1186
Table 1 (Continued)
Trace
elements
Chelating Sorbent
agent
added
Eluent
Analysis method Recovery
(%)
Loading
time
(volume)
Preconcentration LOD
factor
(ngyl)
Sampling Ref.
frequency
(hy1)
Sea water,
industrial
effluents
Cr(III),
Cr(VI),
Cr(total)
DDTC
C18-silica
MeOH
F-AAS
95–105
60–300 s
90–500
20
30
w59x
Sea, river
waters
Certified low
alloy steel,
mussel,
tomatoe leaves
Certified
biological,
vegetable
samples
Cr(VI),
Cr(total)
Co
DDTC
C18-silica
EtOH
ET-AAS
101–105
12
w60x
C18-silica
Acidified F-AAS
EtOH
98–102
17.2
1600–
1800
3200
22
NN
1 min
(3 ml)
30 s
(3.25 ml)
90
w61x
Pb
DDTC
C18-silica
IBMK
F-AAS
99.2–
137.9
2–10 min
60–189
3000
24
w62x
Standard
solutions
Pb
DDTP
C18-silica
EtOH
F-AAS
—
300–3000
—
w63x
Certified citrus
leaves,
marine
sediment
Standard
solutions
MeHg,
Hg(II)
DDTP
C18-silica
EtOH
CV-AAS
99.6–
112.5
2.5–75
14–1000
min
(10–150
ml)
4.5 min
20
(23.85 ml)
10
12
w64x
Cu, Pb
MeOH
F-AAS
—
80 s
(4 ml)
14–60
4000–
10 000
—
w65x
Sea water
Cu
HCl
ET-AAS
93.2–99.6
33
5
35
w66x
Pharmaceutical
preparations
Sea water
Zn
DDTC, 8- C18-silica
quinolinol
or PAR
None
TAN-loadedC18-silica
None
TAN-loadedC18-silica
None
FZ-loadedC18-silica
ZrO2
None
HCl
Spectrophotometry
Spectrophotometry
ICP–AES
—
10 000
45
w67x
0.1–
0.3 nM
6–90
—
w68x
—
w69x
River, tap, rain
waters
Fe(II),
Fe(III)
Al, Bi,
Cd, Co,
Cr, Cu,
Fe, Ga,
In, Mn,
Mo, Ni,
MeOH
HNO3
1 min
(3 ml)
89.8–107.8 —
—
95.4–99
2–20 min 6–60
(4–40 ml)
33 min
100
(100 ml)
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
Table 1 (Continued)
Matrix
Urine
Eluent
Analysis method Recovery
(%)
NHq
ICP–AES
4
HNO3 or F-AAS
NHq
4
HNO3 or F-AAS
NHq
4
HNO3
ICP–AES
Loading
time
(volume)
Preconcentration LOD
factor
(ngyl)
Sampling Ref.
frequency
(hy1)
—
90–106
(2 ml)
35 s
10
25
200
800–1000
—
55
w70x
w71x
86–117
—
—
—
w72x
)93
(10 ml)
50
42 000–
81 000
50
—
w73x
1 min
(12 ml)
3 min
(37.8 ml)
340
50
40
w48x
80
800
18
w49x
None
None
Acidic Al2O3
Acidic Al2O3
None
Al2O3
None
Basic Al2O3
Cu
APDC
PTFE turnings IBMK
F-AAS
94–102
Cr(VI)
APDC
PTFE turnings IBMK
F-AAS
95.5–
100.5
Pb
APDC
PTFE turnings IBMK
F-AAS
95–102
3 min
(39 ml)
330
800
15
w50x
Cr(VI)
APDC
PTFE (KR)
EtOH
ET-AAS
105
19
4.2
21.2
w74x
Cr(VI)
APDC
PTFE (KR)
EtOH
ET-AAS
—
1 min
(5 ml)
1 min
(5 ml)
16.3
16
16.7
w75x
Cd, Co, Cu, Dithizone PTFE (KR)
Zn
IBMK
F-AAS
95.3–
108.4
1 min
(5 ml)
23.4–69.3
1060–
2560
18
w76x
Cd
DDTC
PTFE (KR)
IBMK
F-AAS
97.9–110
50 s
(4.2 ml)
30
100
55
w77x
Cr(VI)
APDC
PTFE beads
EtOH
ET-AAS
104–108
1 min
(5 ml)
30.1
8.8
16.7
w75x
1187
Organic sorbents
Tap, river,
coastal waters
Tap, river,
coastal,
industrial
waste waters
Tap, river and
coastal
waters,
marine
sediment,
fish and
mussel tissues
Drinking, sea
waters
Certified natural
water, sea
water
Certified
human air, pig
liver, sea
prawn
Certified
humain hair
and rice
powder
Certified natural
water, sea
water
Pb, Tl,
V, Sb,
Sn, Zn
Cr(VI)
Cr(III),
Cr(VI)
Cr(III),
Cr(VI)
Cr(III)
Chelating Sorbent
agent
added
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Waters
Lake, river,
tap waters
Sewage waters
Trace
elements
1188
Table 1 (Continued)
Trace
elements
Chelating Sorbent
agent
added
Eluent
Analysis method Recovery
(%)
Standard
solutions
Pb
DDTP
PUF
EtOH
F-AAS
Certified
seawaters
Standard
samples
Alloys, ores
Cu
None
None
HClEtOH
HCl
F-AAS
Cd, Zn
Pd, Pt, Rh
ODETA
HClEtOH
Cu, Cd,
Ni
Cu, Cd,
Pb
Cr(III)
—
PAN-coatedXAD-4
BSQ-loadedXAD-7
Highly crosslinked
polystyrene
IDA-Novarose
Sulfasarzene
None
Cu, Cd,
Ni,
Zn, Mn
Cd, Cu,
Pb, Zn
Cr(VI),
Cr(total)
Cd, Ni, Pb
None
Cu
Cd
Bathocuproine
None
Pb
DDTP
Tap water
River, ground
waters
River, mineral
and tap
waters
Estuarine
waters
Synthetic sea
water
Natural waters
Certified pig
kidney, rye
grass, rice
flour, tomato
leaves
Ground
water
Water, vegetable samples
Standard
solutions
None
DPC
None
Loading
time
(volume)
Sampling Ref.
frequency
(hy1)
14–1000
300–3000
—
w63x
29.1–296.1
60–600
—
w32x
10
1600–
1900
3000–
8000
—
w78x
30
w79x
F-AAS
2.5–75
min
(10–150
ml)
99.6–103 (2.5–
25 ml)
—
20 s
(0.1 ml)
77.8–103.6 1 min
—
HCl
ICP–AES
—
10 min
500–1000
—
—
w80x
Lewatit
TP807’84
PAPhA
HCl
80–120
50 min
(100 ml)
90 s
(6.6 ml)
50
w33x
35
2000–
5500
200
—
HCl
Spectrophotometry
F-AAS
30
w81x
Toyopearl AFChelate 650
M
Cation
exchanger
Cation
exchanger
Cation
exchanger
HNO3
ICP–MS
87–10
1 min
(1 ml)
—
1.4–86
—
w82x
HNO3
F-AAS
—
—
50–105
30–200
60
w45x
HNO3acetone
HCl
Spectrophotometry
ICP–MS
93–08
—
—
8.9–15.2
—
w83x
96.7–03.7
2 min
(7.8 ml)
10
1000–4000
90
w84x
HNO3
Spectrophotometry
Spectrophotometry
F-AAS
—
10 min
(8.3 ml)
90 s
(5 ml)
2.5–75
min
(10–150
ml)
—
80
—
w85x
—
230
20
w86x
14–1000
300–3000
—
w63x
Anion
exchanger
Anion
exchanger
Activated
carbon
HNO3
EtOH
Fluorimetry
—
Preconcentration LOD
factor
(ngyl)
97–01
94–104
—
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
Table 1 (Continued)
Matrix
Trace
elements
Eluent
Analysis method Recovery
(%)
Loading
time
(volume)
Preconcentration LOD
factor
(ngyl)
Sampling Ref.
frequency
(hy1)
Steels, Al solutions Bi
DDTP
EtOH
ET-AAS
87–104.3
48
7
w87x
Cu
APDC
IBMK
F-AAS
88–113
4 min
(10 ml)
2 min
(4.5 ml)
14
Tap, mineral,
well, river,
swimming
pool waters
Silicon, tap
water
Rock, copper
ore
Activated
carbon
Activated
carbon
100
600
17
w88x
Fe
None
HCl
MPT–AES
97.4–105
1000–36 000 —
w89x
None
1 min
(1.2 ml)
3 min
(15.6 ml)
4.3–6.4
Pd
Activated
carbon
Activated
carbon
145
300
w90x
Thiourea F-AAS
103–107
15–20
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Chelating Sorbent
agent
added
1189
1190
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
be used as eluting solvents leading to a high
sensitivity in flame AAS. Complexing reagents
are, therefore, added for efficient retention of trace
metals. Their choice is based on their fast reaction
with metals, such as diethyldithiocarbamate
(DDTC) and ammonium pyrrolidine dithiocarbamate (APDC) w56,59,60,62,91x. In addition, both
reagents are water soluble and do not adsorb on
C18-silica so that it does not overload with the
reagent itself. However, these reagents lack selectivity, so that other reagents have been used for
particular applications, like 1-10-phenanthroline
w57x, 4-(2-pyridylazo)resorcinol (PAR) or 2-(2pyridylazo)-5-dimethylaminophenol (PADMAP)
w58x, 0,0-diethyl-dithiophosphate (DDTP) w63x, lnitroso-2-naphthol (NN) w61x. l-(2-tiazolylazo)-2naphthol (TAN) w66x. The microcolumn can be
inserted into the tip of the PTFE capillary in the
autosampler arm of a graphite furnace atomic
absorption spectrometer w56x.
Even though C18-silica has been the most frequently used sorbent for FI preconcentration, other
sorbents were found satisfactory for some applications as shown in Table 1, such as functionalized
silica w51–53x, alumina w70–73x, activated carbon
w63,87–90x, polyurethane foam (PUF) w63,92x, or
PTFE turnings w48–50x. A particular knotted reactor (KR) has been recently developed, which
consists of a long tube properly knotted usually
made of PTFE. The trace element species are
adsorbed on the inner wall of the tubing as
indicated by scanning electron microscopy w77x.
This reactor allows higher sample loading volumes
than micro-columns due to its lower back-pressure.
In addition, the inner wall may be precoated with
a hydrophobic ligand for subsequent retention of
trace elements w93x. However, on the other hand,
lower enrichment factors are attained as compared
to micro-columns w75x. For that reason, in case of
trace metals, micro-columns are usually preferred
for the achievement of low levels of determination.
2.3.4.3. On-line coupling to ICP–AES or ICP–
MS. The first report of FI on-line preconcentration
coupled to ICP-atomic emission spectrometry
(AES) appeared nearly twenty years ago w94x.
Since then, several studies have used this coupling
with different sorbents such as ZrO2 or function-
alized silica gel for example w51,69x. Similarly,
numerous studies have reported on-line coupling
to ICP–MS, as noted earlier w95x. A few examples
are given in Table 1 w82,84x.
2.3.4.4. On-line coupling to spectrophotometry.
Spectrophotometry offers the advantage of requiring inexpensive and very common instrumentation.
In addition, by choosing a non-selective chromogenic reagent, multi-metal determinations may be
possible w33x. Its coupling to FI analysis is well
suited for monitoring purposes and a few studies
present such systems as indicated in Table 1
w33,52,68,86x. Solid-phase spectrophotometry
(SPS) has also been reported with FI systems due
to its simplicity and low detection limits. The solid
sorbent is packed in either commercially available
or customized flow cells. With such systems the
retained analytes are periodically removed from
the flow cell using an acid or a complexing
solution w67,83,85x.
On-line FI sorbent extraction procedures have
several advantages over the corresponding off-line
methods: higher sample throughput (increased by
1 to 2 orders of magnitude), lower consumption
of sample and reagent (also reduced by 1 to 2
orders of magnitude), better precision (with relative standard deviations approx. 1–2%), lower risk
of loss or contamination and easy automation.
However, the FI method by using column extraction has some disadvantages. In particular, it may
suffer from insufficient adsorption on the resin and
clogging of the column when insoluble ligands are
used w96x.
3. Step-by-step method development guide
Development of an SPE method can be considered as a two-step procedure. First, the most
appropriate sorbent for the application should be
chosen (the following is intended to help the reader
in choosing a solid sorbent for trace element
determination). Optimization of the most influential parameters should then be undertaken. Obviously, optimization should initially be performed
using spiked synthetic solutions, but it must be
followed by the use of certified reference materials
or spiked real samples, as matrix components
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
(such as ligands or other ions) may change the
trace element retention on the sorbent, thereby
decreasing recoveries of the target species.
3.1. Selection of solid sorbent
Solid sorbents may be hydrophobic or polar. It
is common to call reversed-phase sorbents the
packing materials that are more hydrophobic than
the sample, which are frequently used with aqueous samples. On the other hand, normal-phase
sorbents refer to materials more polar than the
sample and they are used when the sample is an
organic solvent containing the target compounds.
When hydrophobic supports are used, retention of
ionic metal species will require the formation of
hydrophobic complexes. This can be achieved
through addition of the proper reagent to the
sample or thorough immobilization of the reagent
on the hydrophobic solid sorbent. Addition of
reagent to the sample is appropriate for the fixation
of unstable metal species (such as Cu(I) and
Fe(II)) to maintain speciation, while immobilization offers the convenience of having a prepared
cartridge or disk before analysis. Immobilization
may also provide a significant development in
speciation analysis, because metal equilibrium in
the sample may not be affected by reaction on the
cartridge.
The nature and properties of the sorbent are of
prime importance for effective retention of metallic
species. Careful choice of the sorbent is thus
crucial to the development of SPE methodology.
In practice, the main requirements for a solid
sorbent are: (1) the possibility to extract a large
number of trace elements over a wide pH range
(along with selectivity towards major ions); (2)
the fast and quantitative sorption and elution; (3)
a high capacity; (4) regenerability; and (5) accessibility. In particular, sorbents that allow fast reaction rates are preferred to achieve faster extraction
as well as higher loading capacities. Hence, sorbents based on hydrophilic macroporous polymers
and cellulose or on fibrous materials provide excellent kinetic properties w97x.
The broad variety of sorbents available explains
one of the most powerful aspects of SPE, which
is selectivity. Sorbents can be mainly categorized
1191
as organic based ones (natural polymers, as well
as synthetic polymers) and inorganic based ones
(silica gel SiO2, alumina A12O3, magnesia MgO
and other oxide species). Immobilization of organic compounds on the surface of the solid support
is usually aimed at modifying the surface with
certain target functional groups for a higher selectivity of the extraction. The selectivity of the
modified solid phases towards certain metal ions
is attributed to several well-known factors, such as
the size of the organic compound used to modify
the sorbent, the activity of the loaded surface
groups, and the type of the interacting functional
group. However, the selective extraction of a single
trace element from other interfering ion(s) represents a direct challenge for finding a suitable phase
capable of exhibiting a sufficient affinity to selectively bind that metal ion. For particular applications, the combination of two sorbents may thus
be advisable. As an example, the passage of water
samples through two successive chelating resins
enabled the determination of trace and major
elements w98x. Similarly, the combination of an
anion and a cation-exchange resin enabled the
speciation of Cu and Mn in milk samples w99x.
3.1.1. Inorganic based sorbents
Inorganic based sorbents are mainly made of
silica gel even though other inorganic oxides may
be used, as discussed later (cf. Fig. 4). Silica gel
based sorbents present the advantages of mechanical, thermal and chemical stability under various
conditions. They frequently offer a high selectivity
towards a given metal ion. However, all silicabased sorbents suffer from different chemical limitations, namely the presence of residual surface
silanol groups (even after an end-capping treatment) and a narrow pH stability range. Applications of such sorbents to off-line SPE are presented
in Tables 2 and 3.
3.1.1.1. Silica gel. Silica gel can be used as a very
successful adsorbing agent, as it does not swell or
strain, has good mechanical strength and can
undergo heat treatment. In addition, chelating
agents can be easily loaded on silica gel with high
stability, or be bound chemically to the support,
affording a higher stability.
1192
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Fig. 4. Sorbents based on inorganic supports.
The surface of silica gel is characterized by the
presence of silanol groups, which are known to be
weak ion-exchangers, causing low interaction,
binding and extraction of ionic species w131x. In
particular, silica gel presents high sorption capacity
for metal ions, such as Cu, Ni, Co, Zn or Fe w132x.
Retention is highly dependent on sample pH with
quantitative retention requiring pH values over
7.5–8, as under acidic conditions silanol groups
are protonated and the ion-exchange capacity of
the silica gel is greatly reduced or even reduced
to zero at low pHs. In addition, this sorbent has a
very low selectivity, and is prone to hydrolysis at
basic pH. Consequently, modification of the silica
gel surface has been performed to obtain solid
sorbents with greater selectivity. Two approaches
are used for loading the surface with specific
organic compounds, chemical immobilization and
physical adsorption. In the first case, a chemical
bond is formed between the silica gel surface
groups and those of the organic compound (functionalized sorbent). In the second approach, the
organic compound is directly adsorbed on the
silanol groups of the silica gel surface (impregnated or loaded sorbent), either by passing the reagent
solution through a column packed with the adsor-
bent, or by soaking the adsorbent in the reagent
solution.
Impregnating reagents are ion-exchangers or
chelating compounds. Numerous reagents have
been investigated for impregnation of silica gel as
a means of increasing retention capacity and selectivity of the sorbent for trace elements, namely
thionalide
(2-mercapto-N-2-naphthylacetamide)
w101,102x,
2-mercaptobenzothiazole
(MBT)
w133x, NN w103x, 8-hydroxyquinoline (8-HQ)
w134,135x, 3-methyl-l-phenyl-4-stearoyl-5-pyrazolone (MPSP) w100x, salicylaldoxime w132x, dimethylglyoxime (DMG) w13x, Aliquat 336 (methyltricaprylammonium chloride) and Calcon (hydrophobic sodium sulfonate) w136x. Examples of
applications are given in Table 2. Increased stability of the sorbent is obtained by the chemical
binding of chelating functional groups on silica
gel w104x. Applications to the determination of
trace elements have been reported for more than
twenty years with several functional groups, such
as amines, dithiocarbamates, iminodithiocarbamates or dithioacetals w13,105,106,137,138x. Careful choice of the bound chelating groups enables
speciation studies. Hence, dithizone-functionalized
silica gel was reported selective towards Hg(II)
Table 2
Applications of off-line SPE to water samples using inorganic supports
Matrix
Silica
Tap water
Trace
elements
CuyCoyNi
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive
capacity
Preconcentration
factor
LOD
(mgyl)
Ref.
MPSP-loadedSiO2
Glass
column
Sample
pH: 4.5
Elution:
HCl 1 M
Sample pH: 4
Washing
elution:
thiourea 0.2
MqHCl 0.1 M
Sample pH: 7
Washing
elution:
NaBoratey
NaOHy
Iodine
(pH 10)
Sample pH: 3.5
Washing
elution:
acetic
acid
Elution:
HCl 10 M
F-AAS
94.6–101
43y45y49
mmolyg
40
60y40y70
w100x
F-AAS
83–99
0.8 mgyg
3200
0.03
w101x
Spectrophotometry
92–95
5.6 mmolyg
—
0.12
w102x
g-Emission
96–98
mmolyg
0.03
10–100
—
w103x
CV-AAS
99–99.5
300 mmolyg
200
3.96
w104x
Sea water
Pd
Thionalideloaded-SiO2
Glass
column
(1 cm
i.d)
Sea water
As(III)
Thionalideloaded-SiO2
Glass
column
(1 cm
i.d)
River and sea
water
Co
NN-loadedSiO2
Glass
column
Spiked tap
water
Hg(II)
Column
Tap and sea
waters
Hg(II)
Spiked tap
and sea
waters
Hg(II)
DithizonefunctionalizedSiO2
DithioacetalsfunctionalizedSiO2
DithiocarbamatesfunctionalizedSiO2
Column
Elution: water
CV-AAS
91–100
917–1100
mmolyg
5
—
w105x
Glass
column
Elution: water
CV-AAS
88–100
0.6–0.983
mmolyg
—
—
w106x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Sorbent
1193
1194
Table 2 (Continued)
Trace
elements
Sorbent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive
capacity
Preconcentration
factor
LOD
(mgyl)
Ref.
Sea water
VyCoyNiy
GayYyMoy
CdyCryPry
NdySmyEu
yGdyTbyDy
yMoyEry
TmyYbyLuy
WyU
8-HQfunctionalizedfluorinated
metal
alkoxide
glass
Column
(6 mm i.d,
30 mm
bed
height)
Washing
sample
pH: 5 Washing
elution: HNO3
0.5 M
backflush
ICP–MS
85–116
—
10
0.00037–
2200 ngyl
w107x
Cr(III)yCr
(VI)
TiO2
78.4–99.2
8125y6983
mgyg
100
0.030y0.024
w108x
CdyCoyCu
yFeyMnyNi
yPb
TiO2
F-AAS
89–100
5000
mgyg
300
0.01–
0.04
w109x
Tap, ground
waters
Cr(III)y
Cr(VI)
Neutral
Al2O3
Column
(1 cm
i.d)
ET-AAS
99–100
—
25
0.01
w110x
Tap, ground
waters
Se(IV)y
Se(VI)
Acidic
Al2O3
Teflon
column
(1 cm
i.d)
Sample pH:
2 or 8 Elution:
HNO3 0.5
or 1 M
Sample pH: 8
Elution:
HNO3 1 M
andyor EDTA
0.1 M
Sample pH:
6.5–7 Elution:
NH3 1 Mq
HNO3 4 M
Sample pH:
2–8 Elution:
NH3 0.1
M and 4 M
ET-AAS
Natural, waste,
sea waters
Glass
column
(1 cm
i.d)
Glass
column
(1 cm
i.d)
ET-AAS
90–98
23.2y2.0
mgyg
16y100
0.049y
0.80
w111x
Other oxides
Rain, river,
sea, tap
waters
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
Table 3
Applications of off-line SPE to water samples using C18-silica based supports
Matrix
Reagent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive
capacity
Preconcentration
factor
LOD
(mgyl)
Ref.
TBT
None
93.5–
111.5
—
1000
—
w24x
TPhT
None
Fluorimetry
81–89
—
100
—
w112x
Sea water
TPhT
None
Conditioning
sample drying
elution:
acidified
ethyl acetate
Conditioning:
MeOHqNaCl
Sample
Washing
Air drying
Elution:
10y4 M FlOH
in MeOH
backflush
Washing
sample
Washing air
drying elution:
MeOH
GC–ECD
Spiked sea
waters
Cartridge
or
Empore
disk
(25 mm)
Bond Elut
cartridge
Fluorescence
(after addition
of flavonol
to the eluate)
—
—
250
—
w113x
ET-AAS
94–97
—
40–75
0.007y0.05
w114x
ET-AAS
67–108
—
50–100
—
w115x
No reagent
Sea water
Addition of the reagent to the sample
Sea water
SeySb
APDC
Sea water
CdyZnyCuy
MnyFeyNiy
Co
8-HQ
Bond-Elut
cartridge
(40 mm)
Glass
column
(1.4 cm
i.d)
Glass
column
(1.4 cm
i.d)
Sample
pH: 1.2
Washing
elution:
MeOH
Sample
pH: 8.9
Washing
(waterq
oxine)
elution:
MeOH
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Trace
elements
1195
1196
Table 3 (Continued)
Matrix
Trace
elements
Reagent
Loaded reagent onto the sorbent
River water
Cu
Neocuproine
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive
capacity
Preconcentration
factor
LOD
(mgyl)
Ref.
Empore
disks
(47 mm)
Washing
conditioning:
MeOH Sample
pH: 5.0 Drying
Spectrophotometry
(454 nm)
99.7–
102.6
940 mg
Cu2q
50–100
0.12
w116x
Spectrophotometry
(484 nm)
—
—
20–40
0.40–3.8
w27x
—
—
0.080
w117x
200
0.14y
0.16y
0.14
w31x
CRM water
(SLRS-3),
lake,
river,
drinking
waters
Cu(I)
Bathocuproine
Bond Elut
cartridge
Empore
disk
Tap waters,
well water
Fe
Bathophenanthroline
Empore
disks
(47 mm)
Synthetic
seawaters
MeHgy
PhHgy
Hg(II)
Dithizone
Sep Pak
cartridge
Rain, lake,
river
waters
MonoBTy
DiBTyTBT
yMonoPhT
yDiPhTyTP
hT
Cu
Tropolone
Sep-Pak
cartridge
Quinone
derivative
Empore
disks
(47 mm)
Tap, well and
river waters
Elution:
isopentyl
alcohol
Conditioning:
MeOHqwater
Sample pH: 4.3
Elution:
MeOHwater 90:10
(vyv)
Washing
activation:
MeOHqwater
Sample
pH: 4–7
Elution:
EtOHq
NaClO4
Sample pH:
4qEDTA
0.001
M Washing
Elution: MeOH
Conditioning:
MeOH sample
pH: 2–3 Air
drying Elution:
diethyl ether
Washing
Conditioning:
buffer sample
pH: 7.0
Drying
Elution: HNO3
0.1 M
Spectrophotometry
(533 nm)
LC–DAD
95–104
Ethylation-GC–
FPD
—
—
—
—
w118x
F-AAS
98.4–102
360 mg
Cu2q
400
0.2
w119x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Operation
Table 3 (Continued)
Trace
elements
Reagent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive
capacity
Preconcentration
factor
LOD
(mgyl)
Ref.
Tap, rain,
snow and
sea waters
Cu(II)
Schiff’s base
(salen I)
Empore
disk
(47 mm)
AAS
—
396 mg
Cu2q
)500
0.004
w34x
Synthetic and
spring waters
Pb(II)
Schiff’s base
Empore
disk
F-AAS
97.1–
100.2
700
mgydisk
50
16.7
w120x
River water
Pb(II)
BAS
Empore
disk
(47 mm)
F-AAS
—
476 mg
Pb2q
G300
0.050
w121x
Sea waters
Fe(II)
Ferrozine
Sep Pak
cartridge
Spectrophotometry
(562 nm)
91
—
40
0.6
nmolyl
w122x
Rain, sea
waters
Fe(II)
Ferrozine
Sep Pak
cartridge
LC–UV
(254 nm)
92–99
—
100–500
0.1 nmolyl
w123x
Certified sea
waters
(NASS-2 and
SLEW-1)
CuyCd
APDC
Teflon
cartridge
(0.94 mm
i.d)
ET-AAS
95.8–
103.3
—
25–50
0.0024y
0.00018
w124x
Tap and
Spring
waters
U(IV)
TOPO
Empore
disk
(47 mm
i.d)
Washing
sample
pH: 5.5–6
Air drying
elution: HNO3
0.1 M
Washing
sample
pH: 2–8 Air
drying Elution:
HNO3 O.5 M
Washing
sample
pH: 2–7 Air
drying elution:
acetic acid 1 M
Conditioning:
MeOHqwater
sample pH:
6.8–8.3
Washing
Elution: MeOH
Conditioning:
MeOHqwater
Sample
Washing
Elution: MeOH
Conditioning:
MeOHqwater
Sample: 6–8
Air drying
Elution:
MeOH
Washing
conditioning
sample elution:
MeOH
Spectrophotometry
85
4033
mgydisk
8
0.1
w125x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
1197
1198
Table 3 (Continued)
Trace
elements
Reagent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive
capacity
Preconcentration
factor
LOD
(mgyl)
Ref.
Sea waters
LayCeyPry
NdySmyEuy
GdyTby
DyyHoy
EryTmy
YbyLu
Bi
HDEHPy
H2ME
HP
Sep Pak
cartridge
Sample
pH:3–3.5
Washing
elution:
HCl 6 M
ICP–MS
88.8–99.8
—
200–1000
—
w126x
Cyanex 301
Cartridge
(0.5 g)
ET-AAS
98.5–100
—
10–100
105
w127x
Sea, well
and tap
waters
Be
Quinalizarin
Sep pak
cartridge
F-AAS
98–101
200 mg
200
0.2
w128x
Tap, spring
waters
Agq
HT18C6
Empore
disk
AAS
996–
100.3
210 mg
Agydisk
200
0.050
w129x
Tap, river,
well and
spring waters
Hg(II)
HT18C6TO
Empore
disk
(47 mm
i.d)
Conditioning:
HCl 0.1 M
Sample
pH: 1
Air drying
Elution:
HNO3 3 M
Washing
conditioning
sample
pH: 6–6.6
Elution:
HNO3 0.5 M
Conditioning:
MeOHqwater
Sample elution:
Na2S2O3 0.1 M
Washing
sample
pH:-7 Air
drying
Elution:
HBr 1 M
CV-AAS
97.1–
101.3
241 mg
Hg2q
50
0.006
w130x
Spiked natural
waters
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w104x, even though dithizone was reported to react
with many trace elements w139x. Similarly, purpurogallin-bound silica gel enabled selective extraction of Fe(III) w140x. Simultaneous retention of
trace elements is possible by choosing a nonselective chelating group, such as N-propylsalicylaldimine w141x or Bismuthol I (2,5-dimercaptol,3,4-thiadiazole) w142x. Acidic groups can also be
used for further chelation of trace elements, such
as phosphonic acid w143x and calixarene tetrahydroxamic acid w144x. Alternatively, macrocycles
may be bound to silica (SGBM) w145x, such as
18-crown-6 (18C6) w146x.
It must be kept in mind that despite chemical
bonding of functional groups on the silica gel
surface, free silanol groups still remain w143x.
Their number can be minimised by end-capping
the sorbent, but some will still be present. As a
consequence, they will participate in the retention
of trace elements somewhat, especially at pHs
above their pKa (ionized form).
3.1.1.2. C18-bonded silica gel. Despite the large
variety of bonded phases available, octadecylbonded silica has currently become the most popular phase used. Numerous applications report the
use of C18-silica, as indicated by the studies
reported for water samples in Table 3. In particular,
organometallic compounds (e.g. tributyltin (TBT),
triphenyltin (TPhT), alkylselenides) can be
retained on this sorbent due to possible hydrophobic interaction w19,24,112,113x. Bare C18-silica can
also retain a fraction of inorganic trace elements,
probably due to the presence of silanol groups on
its surface w34x. However, in practice, due to its
hydrophobic character, C18-silica is not well suited
for retention of trace element species, as the latter
are often polar or ionic. Retention on C18-silica
may be improved by addition of a ligand reagent
to the sample before its percolation through the
sorbent. The hydrophobic part of the ligand will
thus have hydrophobic interaction with the C18silica and be retained on the sorbent, while the
functional group of the ligand will ensure chelation
of the trace element. Among reagents, one can cite
8-HQ w115x, APDC w114x, 1,10-phenanthroline
w18x, or bathocuproine w27x.
1199
An alternative approach is to form the complex
by passing the sample through a C18-silica containing the immobilized reagent. Octadecyl bonded
silica, modified by suitable ligands has been successfully used for the separation and sensitive
determination of metal ions. Examples are given
in Table 3. The careful choice of the ligand may
add selectivity to the extraction step, favoring
speciation. For example, salen I-modified C18silica was found selective for Cu(II) w34x, while
impregnation of C18-silica with neocuproine was
suitable for Cu(I) w116x. C18-silica
{ coated with bis
wl-hydroxy-9,10-anthraquinone-2-methylxsulfide
(BAS) was preferred for Pb(II) retention w121x,
while coating with N,N9-diethyl-N9-benzoylthiourea
(DEBT) was recommended for Pd w147x. Macrocycles may also be loaded on C18-silica and efficiently used for the retention of trace metals, such
as hexathia-18-crown-6 (HT18C6) w129x or calixarene hydroxamate w144x.
For some particular applications, mixed ligand
complexes may be used to ensure synergistic
adsorption of the metal complex on the solid
sorbent. Thus, while Cu(II) ions cannot complex
with neutral tri-n-butyl phosphate (TBP) molecules adsorbed on C18-silica, the form of Cu(TTA)
complex (TTA being 2-thenoyltrifluoroacetone)
was retained at approximately 80% w148x. Alternatively, in some cases, loading the chelating agent
on C8-silica instead of C18-silica may give better
results as observed for the retention of bismuth on
oxinate-loaded reversed phase w149x.
Despite their broad application to trace element
preconcentration, bonded silica phases (either C18silica or functionalized-silica gel) present the
drawback of a limited range of pH that can be
used, as in acidic (below 2 to 4) and basic (above
8) pHs hydrolysis may occur, which changes the
interactions that occur between the sorbent and the
trace elements. As a consequence, polymeric sorbents may be preferred.
3.1.1.3. Other inorganic oxides. Apart from silica
other inorganic oxides have been tested for the
adsorption of trace elements as shown in Tables 1
and 2. Whereas SiO2, due to its acidic properties,
is expected to adsorb only cations, basic oxides
(such as magnesia MgO) should adsorb only
1200
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Fig. 5. Sorbents based on organic supports.
anions. As a matter of fact adsorption of ions on
oxide surfaces is believed to proceed with participation of hydroxyl groups. These groups are negatively charged (deprotonated) under basic
conditions, thereby retaining cations and positively
charged (protonated) under acidic conditions,
thereby retaining anions. Consequently, on amphoteric oxides (namely titania TiO2, alumina Al2O3,
zirconia ZrO2), cations are adsorbed under basic
conditions (pH above the isoelectric point of the
oxide which was reported to be 6.2 for TiO2
w109x) while anions are adsorbed under acidic
conditions (pH below the isoelectric point of the
oxide). For example, chromium speciation may be
achieved by careful adjustment of the sample pH:
pH 2 and 7 for retention of Cr(VI) (anionic) and
Cr(III) (cationic), respectively, on acidic alumina
w70,71x; pH 2 and 8 for retention of Cr(VI) and
Cr(III) on titania, respectively w108x. The concurrent adsorption of Hq is responsible for the
absence of retention of cationic species at very
low pHs. However, changing the sample pH may
affect speciation and should be avoided as far as
possible. So it may be preferred to find a suitable
sorbent for retaining the targeted species with
subsequent selective elution for further speciation
studies. With regards to chromium speciation, neutral alumina has been used for that purpose
w110,150x.
The preparation technique is of prime importance w109x, as the adsorption properties of many
oxides strongly depend on the characteristics of
the solid, namely crystal structure, morphology,
defects, specific surface area, hydroxyl coverage,
surface impurities and modifiers. Thus, the coating
of acidic alumina with an anionic surfactant
allowed the selective retention of Cr(VI) in very
acidic solutions w151x. Adsorption on inorganic
oxides may also be influenced by the presence of
salts in the matrix. In particular, high concentrations of phosphates and sulfates may decrease
trace element retention on titania w152x. On the
opposite, major cations (Naq, Kq, Ca2q, Mg2q)
are weakly adsorbed on titania w152,153x.
3.1.2. Organic based sorbents
Organic based sorbents may be divided into
polymeric and non-polymeric sorbents, as shown
in Fig. 5. Polymeric sorbents have been, by far,
the most used for trace element preconcentration
having the advantage over bonded silica in that
they can be used over the entire pH range. Their
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
disadvantage is that the conditioning step is more
time consuming as they require extensive cleaning
before use. Comprehensive reviews on polymeric
phases have been published w97,154x. Masque´ et
al. published an extensive review on sorbents used
for the SPE of polar organic micropollutants from
natural waters w155x. The purpose of this section
is to summarize the most frequently used organic
based sorbents for trace elements, as well as the
more recently reported ones.
In most applications, new sorbents have been
synthesized by chemically bonding chelating
groups to polymeric cross-linked chains and characterizing their ability to selectively adsorb trace
elements. Most of the chelating groups reported
have low water solubility to avoid their leaching
from the sorbent, as most applications deal with
aqueous samples. At the same time, a too hydrophobic group will hinder wettability of the sorbent
by the aqueous sample, resulting in poor retention
efficiency. A compromise is thus necessary. In
addition to the functional group, the efficiency of
polymeric sorbents depends on various physicochemical parameters, such as particle size, surface
area, pore diameter, pore volume, degree of crosslinking and particle size distribution.
3.1.2.1. Polystyrene-divinylbenzcne based sorbents. Macroporous hydrophobic resins of the
Amberlite XAD series are good supports for developing chelating matrices. Amberlite XAD-1,
XAD-2, XAD-4 and XAD-16 are polystyrenedivinylbenzene (PS-DVB) resins with a high
hydrophobic character and no ion-exchange capacity. In addition to the hydrophobic interaction that
also occurs with C18-silica, such sorbents allow
p–p interactions with aromatic analytes.
Due to the hydrophobic character of PS-DVB,
retention of trace elements on such sorbents
requires the addition of a ligand to the sample.
Inorganic ligands may be used w156x, but organic
ligands are preferred, such as APDC w157,158x, 8HQ w159,160x, or diphenylcarbazide (DPC) w161x.
Alternatively, ligands may be attached to the PSDVB by physical adsorption such as dithizone
w162x, PDT (3-(2-pyridyl)-5,6-diphenyl-l,2,4-triazine) w4x, tropolone w163,164x, l-(2-pyridylazo)2naphthol (PAN) w32,165x, DDQ (7-dodecenyl-
1201
8-quinolinol) w166x, APDC w167x or 5-BrPA-DAP
(2-(5-bromo-2-pyridylazo)-5-(diethylamino) phenol) w168x. Macrocycles can also be adsorbed,
such as calixarene hydroxamate w144x. However,
in practice, the resins prepared by impregnation of
the ligand are difficult to reuse, due to partial
leaching of the ligand (thus resulting in poor
repeatability). To overcome this problem, the resin
may be chemically functionalized. Several chemical modifications of PS-DVB have recently been
reviewed w169x, but only a few are commercially
available. The ligands are generally coupled to a
methylene or an azo spacer on the matrix. Among
{ligands, one can cite Alizarin Red-S w170x, salicylic acid (SA) w171x, thiosalicylic acid (TSA)
w172x, pyrocatechol violet (PV) w173x, chromotropic acid (CA) w174x, pyrocatechol (PC)
w175,176x, Tiron (disodium salt of l,2-dihydroxybenzene-3,5-disulfonic acid) w177x, quinalizarin
(1,2,5,8-tetrahydroxy-anthraquinone) w22x, bicine
wN,N-bis (2-hydroxy-ethyl) glycinex w178x, and
poly(dithiocarbamate) (PDTC) w179x.
Of great interest are also the sulfonated PSDVB resins, as they show excellent hydrophilicity
and high extraction efficiencies for polar organic
compounds w154,155x. In the case of rapid sulfonation under mild conditions, a mixed-mode retention can be observed: adsorption of neutral
compounds on the polymeric resin, and cation
exchange of ionic species on sulfonate groups
w180x. The use of a particular sulfonated PS-DVB
resin has been recently reported to enable chromium speciation w181x. 2-Naphthol-3,6-disulfonic
acid (NDSA) has been coupled to the PS-DVB
through an azo function. In that way, the formation
of an azo cation at very low pHs enabled retention
of the anionic Cr(VI), whereas the sulfonate group
enabled retention of Cr(III) in neutral and basic
media w181x. For particular applications, trimethylammonium functionalized PS-DVB may also be
used with anion-exchange properties.
As summarized in Table 4, which presents
selected applications of polymeric sorbents for the
preconcentration of trace elements from water
samples, even though PS-DVB has been probably
the most widely used of polymers, others also
have been successfully used as detailed below.
1202
Table 4
Applications of off-line SPE using polymeric sorbents to water samples
Matrix
Trace
elements
Adsorptive resins
Tap water
CdyCuy
MnyNiy
PbyZnq
8-HQ
Operation
XAD-2
Polypropylene Conditioning
column
sample
pH: 8–9
Elution:
HCl 2 M
Glass column Washing
(1 cm i.d)
sample
pH: 1
Elution:
H2SO4 0.05
MyMeOH
Glass column Washing
(0.9 cm i.d)
conditioning
sample pH: 6
Elution:
acetone
Column
Washing
(4 mm i.d)
sample
pH: 8
Elution:
EtOHy
HNO3 2 M
Syringe barrel Purification
sample
pH: 11
Elution:
HCl 2 M
Tap water
Cr(VI),
total
CrqDPC
XAD-16
Drinking and
sea waters
BiyCdyCoy
CuyFeyNiy
PbqAPD
C
Chromosorb102
Tap, mineral,
river
waters
Coq8-HQ
Chromosorb105
Tape, lake,
waste
waters
Cr(III)
Cellulose
Chelating resins
Waters
TBT
TropoloneloadedXAD-2
Glass column
(1.5 cm i.d)
Experimental
conditions
Sampleq
0.8%
H2SO4
Washing
Elution:
IBMK
Analysis
method
Recovery
(%)
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
Ref.
ICP–AES
82.3–
97.2
—
F-AAS
100
—
w160x
97.3–99.0 0.4
mgyg
5.25
45
w161x
F-AAS
95–110
300
0.10–11
w158x
ET-AAS
95.2–99.2 —
80
0.0134
w182x
ET-AAS
98–99.3
—
100
0.0018
w183x
ET-AAS
104
—
80
0.0144
w164x
—
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Sorbent
Table 4 (Continued)
Trace
elements
Sorbent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
Ref.
Sea water
CoyCuy
FeyNiy
Zn
PDT-loadedXAD-2
Column
(0.9 cm i.d)
F-AAS
96.3–
103.5
—
—
—
w4x
Well water,
river water
CuyCdy
CoyPby
ZnyMn
QuinalizarinfunctionalizedXAD-2
Glass column
(1 cm i.d)
Washing
elution:
MeOH in
Soxhlet
apparatus
Washing
sample
pH: 5–7
Elution:
HNO3 4 M
F-AAS
91–98
100y50y40y50y
100y65y65
2.0y1.3y5.0y w22x
15.0y1.0y1.6
Well waters
ZnyCdy
PbyNi
PVfunctionalizedXAD-2
Glass column
(1 cm i.d)
F-AAS
98
60y50y
23y18
—
w173x
Well waters
ZnyPb
Salicylic acidfunctionalizedXAD-2
Glass column
(1 cm i.d)
F-AAS
98–100
3.15y
1.70y
1.62y
5.28y
1.42y
0.94y
2.19 mgyg
1410y
1270y
620y
1360
mgyg
1146y461
mgyg
180y140
—
w171x
Well waters
ZnyCdy
PbyNi
Alizarin Red-SfunctionalizedXAD-2
Glass column
(1 cm i.d)
F-AAS
95–100
511y124y
306y124
mgyg
40
10
w170x
River waters
CuyCdyCo
TironyNiyPbyZny functionalizedMnyFe
XAD-2
F-AAS
91–99
—
25–200
0.5–24
w177x
Glass column
(1 cm i.d)
Washing
sample
pH: 3–7
Elution:
HNO3 4 M
Washing
sample
pH: 5.0
Elution:
HCl 1
M-2–4 M
Washing
sample
pH: 4–6
Elution:
HNO3
1–4 M or
HCl 4 M
Washing
sample
pH: 4–7.5
Elution:
HNO3 4 M
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
1203
1204
Table 4 (Continued)
Trace
elements
Sorbent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
Ref.
River waters
CdyCoyCu
yNiyFeyZn
CAfunctionalizedXAD-2
Glass column
(1 cm i.d)
Washing
sample
pH: 4–7
Elution:
HNO3 or
HCl 2 M
F-AAS
95–100
River and tap
waters
Pb
CAfunctionalizedXAD-2
Glass column
(1 cm i.d)
F-AAS
97
River and tap
waters
CdyCoyCu
yFeyNiyZn
PCfunctionalizedXAD-2
Glass column
(1 cm i.d)
F-AAS
—
River and tap
waters
Pb
PCfunctionalizedXAD-2
Glass column
(1 cm i.d)
F-AAS
River and tap
waters
Pb
TSAfunctionalizedXAD-2
Glass column
(1 cm i.d)
Tap, river
waters
CdyCoyCuy
FeyNiyZn
TSAfunctionalizedXAD-2
Glass column
(1 cm i.d)
Washing
sample
pH: 3–8
Elution:
HNO3
2–10 M
Washing
sample
pH: 3–6.5
Elution:
HNO3 2 M
Washing
sample
pH: 5–7.5
Elution:
HNO3 1 M
Washing
sample
pH: 4
Elution:
HNO3
0.5–2 M
Washing
sample
pH: 3.5–7
Washing
elution:
HNO3 2 M
9.35y
3.84y
8.50y
3.24y
6.07y
9.65
mgyg
186.3
mmolyg
100–200
—
w174x
200
4.06
w176x
0.023–
0.092
mmolyg
80–200
—
w175x
94
104.7
mmolyg
100
3.80
w176x
F-AAS
93
89.3
mmolyg
100
4.87
w176x
F-AAS
92–98
197.5y
106.9y
214.0y
66.2y
309.9y
47.4
mmolyg
180–400
0.48y0.20y
4.05y0.98y
1.28y3.94
w172x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
Table 4 (Continued)
Matrix
Trace
elements
Artificial sea
water,
natural
waters
Sorbent
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
CdyCuyMny APDC-loadedNiyPbyZn
XAD-4
Glass column
(0.9 cm i.d)
Sample
pH: 5.0
Washing
elution:
HNO3 4 M
ICP–AES
Artificial sea
water,
natural
waters
CdyCuy
MnyNiy
PbyZn
pipDTC-loadedXAD-4
Glass column
(0.9 cm i.d)
Sample
pH: 5.0
Washing
elution:
HNO3 4 M
ICP–AES
Sea water
AgyAly
BiyCdy
CuyFey
GayMny
NiyPbyTi
DDQ-loadedXAD-4
F-AAS or ETAAS
Tap water
CuyMnyZn
Calixarene
TetrahydroxamateloadedXAD-4
F-AAS
—
Tap and
mineral
waters
Mn
PDTCfunctionalizedXAD-4
F-AAS
97.2
Spiked
solutions
CoyCuy
FeyHgy
NiyPbyZn
BicinefunctionalizedXAD-4
Teflon column Washing
(8 mm i.d)
sample
pH: 8
Washing
elution:
HCl 2 M
Backflush
Plastic
Sample
cartridge
pH: 8.5
(0.9 cm i.d)
Elution:
acidified
water
(pH 2.0)
Glass column Conditioning
(1 cm i.d)
sample
pH: 10
Elution:
HNO3 8 M
Glass column Conditioning
sample
pH: 5.5–7
Elution:
HCl 1 M
98.2–99.6 9.47y
11.08y
8.62y
7.21y
10.25y
10.62
mgyg
97.6–99.1 9.18y
10.76y
8.17y
7.46y
9.86y
10.28
mgyg
73–107
0.55
mmolyg
ET-AAS
97.6–99.1 0.32–0.44
mmolyg
Ref.
180y230y120y
130y160y215
0.1y0.4y0.3y w167x
0.4y0.6y0.5
150y200y140y
120y150y200
0.7y1.0y0.8y w167x
0.9y1.7y1.2
62.5
0.00016–0.3 w166x
—
25
—
w144x
9.1
mmolyg
20
0.5
w179x
40–50
—
w178x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Operation
1205
1206
Table 4 (Continued)
Trace
elements
Sorbent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Waste waters
Cr(III)yCr
(VI)
NDSAfunctionalizedPS-DVB
Glass column
(1 cm i.d)
F-AAS
85.9–96.1 0.40y1.18
mmolyg
20
—
w181x
River water
Hg(II)
PAAfunctionalizedPS-DVB
Glass column
(1 cm i.d)
Spectrophotometry
96
0.6
mmolyg
30
—
w184x
River and
tap
waters
Pb
XO-loadedXAD-7
Glass column
(1 cm i.d)
F-AAS
91
16.9
mmolyg
100
2.44
w176x
River waters
CdyCoyCu
yFeyNiyZn
XO-loadedXAD-7
Glass column
F-AAS
96–100
1.6–2.6
mgyg
10–200
9y24y6y
6y3y21
w185x
River and
reservoir
waters
Cr(III)
8-HQfunctionalizedpolyacrylonitrile
Glass column
(4 mm i.d)
ICP–MS
98–105
41.7
mmolyg
5
0.06
w186x
Aqueous
AuyPty
sample
PdyIr
from a nonferrous metal
smelter
Aminothioureafunctionalizedpolyacrylonitrile
Glass column
(0.5 cm i.d)
ICP–AES
97–99
2.80y
1.75y
1.56y
1.15
mmolyg
6–65
—
w187x
Sea water
Aminophosphonic- Glass column
dithiocarbamate(4 mm i.d)
functionalizedpolyacrylonitrile
Sample pH:
1.5 or 6
Elution:
HCl 4 M
Conditioning
sample
pH: 5.4
Elution:
H2SO4 2 M
Washing
Sample
pH: 5
Elution:
HNO3 1 M
Sample
pH: 4–5
Elution:
HCl 1 or 2 M
Washing
sample
pH: 6
Washing
Elution:
HCl 2 My
HNO3 0.1 M
Washing
sample
pH: 2
Washing
elution:
HCl 4 My
CS(NH2)2 3%
Sample
pH: 6
Washing
elution:
HCl 2 M
ICP–MS
93–104
0.83–74.1
mmolyg
200
0.002–0.601 w188x
ngyl
BeyBiy
CoyGay
AgyPby
CdyCuy
MnyIn
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
Ref.
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
Table 4 (Continued)
Trace
elements
Sorbent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
Ref.
River, lake
and rain
waters
Hg(II)y
MeHg
Dithiocarbamatefunctionalizedpolyvinyle
Column
(1.5 cm i.d)
CV-AAS
91–95
—
667
0.0002
w189x
Sea water
CdyCuy
MnyNiy
PbyZn
Chelamine
Column
ET-AAS
91–102
1
mmolyg
200
0.0023–
0.033
w190x
Sea water
CdyCoy
CuyMny
NiyPbyZn
Chelex-100
Column
ET-AAS or
F-AAS
)98
—
50
0.001–0.1
w191x
River water,
seawater
CdyPbyZn
Amberlite
IRC-718
Glass column
(0.5 cm i.d)
F-AAS
63–104
1.06y
0.096y
1.77
mmolyg
10
—
w192x
Ground and
fresh
waters
Se(IV)ySe
(VI)y
SeCyst
Amberlite
IRA-743
Glass column
(1 cm i.d)
Washing
Sample
pH: 1–11
Elution:
thiourea
5% in HCl
Washing
sample
pH: 6.5
Washing
elution:
HNO3 2 M
Sample
pH: 6.5
Washing
elution:
HNO3 2 M
Washing
conditioning
sample
washing
elution:
HNO3
Washing
conditioning
sample
elution:
HClO4 1
Mqwater
LC–ICP–
MS
93–97
—
55
0.010
w193x
Anion
exchanger
(SAX)
Cartridge
(0.5 g)
—
—
8
w194x
Ion exchangers
Waste water
Cr
Activation:
MeOHq
buffer
Sample
pH: 4.5
Elution:
Na2SO4
0.5 M
Spectro80–98.8
photometry
(544 nm) after
reaction DPC
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
1207
1208
Table 4 (Continued)
Trace
elements
Sorbent
Operation
Experimental
conditions
Analysis
method
Recovery
(%)
Adsorptive Preconcentration LOD
capacity
factor
(mgyl)
Ref.
Sea, river,
tap
waters
Se(IV)y
Se(VI)
Anion
exchanger
(SAX)
Cartridge
GC–MS
91–99
—
40–500
1600y
1400
w19x
River, spring,
waste
waters
Be
Anion
exchanger
Column
(1 cm i.d)
Conditioning
Sample
pH: 7
Elution:
HCOOH 1
MqHCl 3 M
Conditioning:
HClqH2Oq
NaOH
Sample
pH: 6–8
Elution:
HCl 1.5 M
F-AAS
95–102.5
—
125
0.045
w195x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Matrix
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
3.1.2.2. Divinylbenzene-vinylpyrrolidone copolymers. Sorbents made of divinylbenzene-vinylpyrrolidone (DVB-VP) copolymers have recently
been developed, such as Oasis HLB w154x. The
hydrophilic N-vinylpyrrolidone
{
affords good wettability of the resin, while the hydrophobic divinylbenzene provides reversed-phase retention of
analytes. This sorbent has been successfully
applied to the determination of polar organic compounds in water samples. It is more convenient to
use, compared to classical sorbents, as it can dry
out during the extraction procedure without reducing its ability to retain analytes. In addition, it is
stable over the entire pH range. However, until
now, no application related to the preconcentration
of trace elements has been reported. Similarly, the
use of Oasis MCX, a sulfonated divinylbenzenevinylpyrrolidone copolymer w154x, may be useful
for the retention of trace element species, as this
sorbent combines the properties of the previous
sorbent with those of a strong cation-exchanger.
Application to the preconcentration of triphenyltin
has been reported w36x.
3.1.2.3. Polyacrylate polymers. Amberlite XAD-7
and XAD-8 are ethylene-dimethacrylate resins.
They are non-aromatic in character and possess
very low ion-exchange capacity. Due to the polarity of acrylates, such resins enable the recovery of
polar compounds. However, this polarity is quite
moderate so that most of the time reagents are
added to increase retention. Direct addition to the
sample is sometimes performed. As an example,
Cu(II) forms a complex with 8-hydroxyquinoline5-sulfonic acid (8-HQ-5-SA), which can be further
retained on Amberlite XAD-8 as an ion-pair with
cetyltrimethylammonium (CTA) w15x. Yet, most of
the time chelating reagents have been loaded on
such resins, mainly Amberlite XAD-7, to increase
their retention capacity for trace elements andyor
their selectivity such as 8-(benzenesulfonamido)quinoline (BSQ) w78x, xylenol orange (XO)
w176,185x, 5-BrPADAP w168x, or dimethylglyoxal bis(4-phenyl-3-thiosemicarbazone) (DMBS)
w196x. Such loaded sorbents are stable for several
months and can be reused. For a higher stability,
chemical binding of the chelating group may be
performed, as reported for dithizone on
1209
poly(ethylene glycol dimethacrylate-hydroxyethylmethacrylate) microbeads w197x.
3.1.2.4. Polyurethane polymers. Due to its sorption
capacity for several trace elements polyurethane
foam has been tested for use in SPE. Most of the
time complexing reagents are added to enhance
the sorption capacity. Hence, PUF coated with
DMG, NN, DDTC or hexamethylenedithiocarbamate (HMDC) was found efficient in retaining
trace elements w198–200x. The chelating reagent
can also be directly added to the sample, and the
metal chelates further retained on PUF, as observed
with thiocyanate complexes w92,201,202x and
DDTP complexes w63x. Very recently, the immobilization of an enzyme (alkaline phosphatase) has
been reported on PUF with further application as
an enzymatic procedure for Pb(II) determination
w203x.
3.1.2.5. Polyethylene polymers. Polyethylene is
also attractive for SPE of trace elements as this
support adsorbs several metal complexed with
hydrophobic ligands. Additionally, the adsorbed
complexes can be eluted with a small volume of
organic solvents permitting high enrichment factors. Polyethylene can also be used in strongly
acidic and basic media and for that reason, it has
been used as a sorbent for the retention of chromium in an acidic medium after the addition of
DPC w204x.
3.1.2.6. Polytetrafluoroethylene polymers. PTFE
can retain trace elements after addition of a chelating reagent to the sample such as APDC, DDTC
or dithizone (DZ) w48–50,74,76x. PTFE may also
be precoated with a suitable ligand, like 2-methyl8-hydroxyquinoline w93x. The sorbent can be used
as PTFE turnings w48–50x, PTFE beads w75x, or
as a PTFE tubing in a knotted reactor w74,76x.
3.1.2.7. Polystyrene polymers. Polystyrene polymers may be an interesting alternative to common
sorbents (namely Amberlites XAD-2 and XAD-8,
C18-silica) when they have a hyper cross-link
structure. The addition of a reagent to the sample
is required to form complexes that are further
retained on the hydrophobic sorbent w79x.
1210
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
3.1.2.8. Polyamide polymers. Polyamide polymers
have been used for the retention of rare earth
elements w205x. A chelating reagent was added to
the sample for complexing the trace elements. This
reagent
Thorin
(o-w3,6-disulfo-2-hydroxy-lnaphthylazoxbenzenearsonic acid) was chosen to
enable interaction with the sorbent through electrostatic forces and non-hydrophobic interaction.
3.1.2.9. Iminodiacetate-type chelating resins. Polymeric resins containing iminodiacetate groups
w–CH2–N(CH2COOy)2 x as active sites (IDA resins) have been widely used for the retention of
trace elements. They have been synthesized by
bonding the iminodiacetate functional groups to
several polymeric sorbents, such as polystyrene
(Chelex-100) w10,29,30,191,206–209x or a highly
crosslinked agarose gel (IDA-Novarose) w80x. The
spacer arm length was found to have an effect on
the formation of metal complex species in the
chelating resin w12x.
A major drawback of such sorbents is that, due
to the weak acid character of the functional group,
the degree of protonation will critically affect the
ability of the resin to retain metal cations. Hence,
for Chelex-100, protonation of the carboxylates
and the donor N atom are reported to be complete
at pH 2.21, while a completely deprotonated form
is reached at pH 12.30. Also, such sorbents are
non-selective, so that trace element retention may
be reduced due to retention of major ions (namely
Ca(II) and Mg(II)) w99,191x. Besides, the presence
of ligands in the sample may prevent trace element
retention on the sorbent due to their complexation
as observed in real waters due to the presence of
organic matter w80,210x.
3.1.2.10. Propylenediaminetetraacetate-type chelating resins. The synthesis of a fine-particle
macroporous polymer-based propylenediaminetetraacetic acid (PDATA) type resin has been recently reported w211x. The structure of this sorbent is
very similar to that of ethylene diamine tetraacetic
acid (EDTA) with a spacer arm enabling the
retention of several trace elements upon chelation.
3.1.2.11. Polyacrylonitrile based resins. Polyacrylonitrile fibers have been functionalized to obtain
ion-exchange chelating sorbents with aminophosphonic, dithiocarbamate or aminothiourea groups
w187,188x. However, as such synthesis are timeconsuming an alternative is to coat the polyacrylonitrile fiber with a proper reagent for further
trace element retention such as 8-HQ w186,212x.
3.1.2.12. Ring-opening metathesis polymerisationbased polymers. A high-capacity carboxylic acidfunctionalized resin has been prepared using
ring-opening metathesis polymerisation (ROMP)
w213x. Electron microscopy revealed that the
obtained material consists of irregularly shaped,
agglomerated particles having a non-porous structure with diameter and specific surface area
dependent on the polymerisation sequence and the
stoichiometries. This material was pH stable and
could be reused. The presence of the carboxylic
groups confers an excellent hydrophilic character
to the sorbent (ensuring a high wettability of the
sorbent by water), while the polyunsaturation of
the carrier chain, as well as the entire backbone
provides for a significant reversed-phase character.
The carboxylic acid groups provide weak coordination sites enabling the retention of rare earth
elements. Similarly, dipyridyl amide-functionalized
resins have been reported to allow the extraction
of ‘soft’ metals such as Pd(II) and Hg(II) w214x.
3.1.2.13. Carbon sorbents. Activated carbon is
prepared by low-temperature oxidation of vegetable charcoals. Due to their large surface areas
(300–1000 m2 yg), these sorbents are well-recognized for their very strong sorption both for trace
organic compounds and trace elements. There is
evidence of two types of adsorption sites on
activated carbons: (1) graphite-like basal planes
that enable adsorption through van der Waals
forces, especially p-electron interactions, and (2)
polar groups like carbonyls, hydroxyls and carboxyls, that may interact via ionic interaction of
hydrogen bonding w215x. Consequently, trace elements may be directly adsorbed on activated carbon w19,216x. Metal chelates may also be retained
on this sorbent after addition of a proper chelating
agent to the sample w17x such as amino acids
w217x, dithizone w218x, APDC w88,219x, PAN
w220x, 8-HQ w221x, cupferron w221x, Bismuthiol II
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
(3-phenyl-5-mercapto-l,3,4-thiadiazole-2(3H)-thione) w222x, or DDTP w63,87x. The ligand should
be chosen to avoid a strong interaction with the
activated carbon otherwise complete dissociation
of the metal chelate would be observed w215x.
The main drawback when using activated carbons is their heterogeneous surface with active
functional groups that often lead to low reproducibility. In addition, these sorbents are very reactive
and can act as catalysts for oxidation and other
chemical reactions. Fortunately, along with the
development of polymer materials and bonded
phases, a new generation of carbon sorbents
appeared in the 1970s and 1980s with a more
homogeneous structure and more reproducible
properties. Graphitized carbon blacks (GCB) are
obtained from heating carbon blacks at 2700–3000
8C in an inert atmosphere w155x. They are nonspecific and non-porous sorbents (surface area
approx. 100 m2 yg), and are considered to be both
reversed-phase sorbents and anion-exchangers due
to the presence of positively charged chemical
heterogeneities on their surface. Such sorbents
have been extensively used in the past few years
for the SPE of polar organic pollutants from water
samples w155x, but their use for trace elements is
still rare w223x. Their main drawbacks are possible
irreversible retention of analytes, which may be
overcome by elution in the backflush mode, and
poor mechanical stability. Porous graphitized carbon (PGC) is a more stable carbon based sorbent
than GCB as the graphite is immobilized on a
silica substrate. So this sorbent should be suitable
for trace element retention even though until now
its applications have been limited to trace organic
compounds.
3.1.2.14. Cellulose. Cellulose was found effective
in retaining trace elements present in water samples either directly or upon addition of a chelating
agent to the sample w183,224x. In particular, the
selective retention of Cr(III) was reported thereby
enabling chromium speciation w183x. This sorbent
may also be functionalized to increase the SPE
selectivity. Thus, selenium speciation has been
reported on cellulose functionalized with quaternary amine due to the selective elution of the
1211
retained Se(IV) and Se(VI) species using nitric
acid at two different concentrations w225x.
3.1.2.15. Naphthalene based sorbents. Retention
of trace elements on microcrystalline naphthalene
is also feasible, either after addition of a ligand to
the sample w226x, or after functionalization of the
solid to ensure better adsorption characteristics
towards trace elements w227,228x. However, the
use of this solid support is rather uncommon. In
addition, until now it has been reserved to batch
experiments.
3.2. Influential parameters
The main experimental variables that affect
analyte recovery by SPE have been extensively
reported by Poole et al. w2,229x. They are briefly
discussed below and illustrated with reported
applications.
3.2.1. Conditioning parameters
3.2.1.1. Washing step. A washing step is highly
recommended, especially when ultratraces of elements are to be determined. Thus, blank extracts
containing trace levels of Zn, Cu and Fe were
suspected to be due to contaminants from C18silica w115x.
3.2.1.2. Conditioning solvent. Even though some
sorbents have been used without a conditioning
step this is not recommended. This step will at
least remove possible remaining contaminants and
air from the sorbent bed. Additionally, in some
cases, this step is crucial for successful retention
of the analytes. The nature of the conditioning
solvent must be appropriate to the nature of the
solid sorbent to ensure good wettability of the
functional groups. As an example with hydrophobic supports such as C18-silica or PS-DVB, quite
polar organic solvents such as methanol should be
used. The sorbent should further be conditioned
by a solvent whose nature is similar to that of the
sample. Thus, for aqueous samples, the solvent
will be water with a pH and ionic strength similar
to that of the sample.
1212
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
require lower maximum flow-rates than disks ranging typically from 0.5 to 5 mlymin. This value
may be increased by a factor of 10 using disks.
Fig. 6. Typical representation of the breakthrough curve (i.e.
concentration of the analyte at the outlet of the SPE system vs.
sample volume percolated through the system). VB is the breakthrough volume, VR the chromatographic elution volume and
VC the sample volume corresponding to the retention of the
maximum amount of analyte, C0 is the initial analyte concentration in the sample.
3.2.2. Loading parameters
3.2.2.1. Sample volume to be percolated. An
important parameter to control in SPE is the
breakthrough volume, which is the maximum sample volume that should be percolated through a
given mass of sorbent after which analytes start to
elute from the sorbent resulting in non-quantitative
recoveries (Fig. 6). The breakthrough volume is
strongly correlated to the chromatographic retention of the analyte on the same sorbent and
depends on the nature of both the sorbent and the
trace element, as well as on the mass of sorbent
considered and the analyte concentration in the
sample w3x. In addition, it depends on the sorbent
containers, as disks usually offer higher breakthrough volumes than cartridges. This volume may
be determined experimentally or estimated using
several methods w229x. For that purpose the nature
of the sample has to be taken into account, as the
possible presence of ligands may dramatically
reduce the breakthrough volume w230x.
3.2.2.2. Sample flow-rate. The sample flow-rate
should be optimized to ensure quantitative retention along with minimization of the time required
for sample processing. This parameter may have a
direct effect on the breakthrough volume, and
elevated flow-rates may reduce the breakthrough
volume w4,229x. As a rule, cartridges and columns
3.2.2.3. Sample pH. Sample pH is of prime importance for efficient retention of the trace elements
on the sorbent. Its influence strongly depends on
the nature of the sorbent used. Careful optimization
of this parameter is thus crucial to ensure quantitative retention of the trace elements and in some
cases selective retention. In particular with ionexchangers, correct adjustment of sample pH is
required to ensure preconcentration. Thus, in the
case of cationic-exchangers, low pH usually results
in poor extraction due to competition between
protons and cationic species for retention on the
sorbent.
When retention of trace elements is based on
chelation (either in the sample or on the solid
sorbent), the sample pH is also a very important
factor as most chelating ligands are conjugated
bases of weak acid groups and accordingly, they
have a very strong affinity for hydrogen ions. The
pH will determine the values of the conditional
stability constants of the metal complexes. By
contrast, pH may have no influence with some
non-ionizable organic ligands w130x.
For inorganic oxides, pH is also of prime importance. In particular, on amphoteric oxides such as
TiO2 or Al2O3, cations are adsorbed at elevated
pHs due to the deprotonation of functional groups,
whereas anion retention requires acidic conditions
for the protonation of functional groups.
3.2.2.4. Sample matrix. The presence of ligands in
the sample matrix may affect trace element retention when stable complexes are formed in the
sample with these ligands, as trace elements are
less available for further retention. Thus, if metals
are present in the sample as strong complexes,
they may not dissociate resulting in no retention
of the free metal on the sorbent. As an example,
reduction in the retention of Cu(II) on Amberlite
CG50 occurs in the presence of ligands such as
glycine w230x. In the case of real samples, the
presence of natural organic matter is of great
concern as it may complex trace elements as
observed for Cu(II) w231,232x. Yet, in some cases
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
the presence of ligands may be a valuable tool for
adding selectivity to the SPE step. This requires
that the added ligands be correctly chosen to
complex only the elements that are not of interest,
so that they are not retained on the sorbent w31x.
The presence of ions other than the target ones
in the sample may also cause problems during the
SPE step. In particular, due to their usually high
levels (e.g. Ca(II)), they may hinder the preconcentration step by overloading the sorbent or cause
interferences during spectrophotometric analysis.
Therefore, their influence should be studied before
validating a SPE method. Sometimes the addition
of a proper masking agent (such as EDTA, thiourea
or ethanolamine for example) may prevent the
formation of interferences due to ions present in
the sample w128x.
Finally, the ionic strength of the sample is
another parameter to control for an efficient SPE,
as it may influence the retention of trace elements,
and thus the value of the breakthrough volume for
a given sorbent w122,195x.
3.2.3. Elution parameters
3.2.3.1. Nature of the solvent. The nature of the
elution solvent is of prime importance and should
optimally meet three criteria: efficiency, selectivity
and compatibility, as discussed below. In addition,
it may be desirable to recover the analytes in a
small volume of solvent to ensure a significant
enrichment factor. The eluent may be an organic
solvent (when reversed-phase sorbents are used),
an acid (usually with ion-exchangers), or a complexing agent.
Firstly, the eluting solvent should be carefully
chosen to ensure efficient recovery of the retained
target species and quantitative recovery as far as
possible. As an example among several solvents
tested for the elution of TPhT from C18-silica
(namely a Triton X-100 surfactant aqueous solution, acetonitrile, tetrahydrofuran (THF), methanol–water 80:20, methanol), only methanol
enabled the achievement of acceptable recoveries
(approx. 85%) w112x.
A further characteristic of the elution solvent
arises with the possibility of introducing selectivity.
Using a solvent with a low or moderate eluting
1213
power, the less retained analytes can be recovered
without eluting the strongly retained compounds.
Thus, if the elements of interest are those that
remain on the sorbent another elution step with a
more eluent solvent will ensure their quantitative
recovery. In that way interferent analytes were
removed during the first eluting step (also called
washing step). On the opposite, if the compounds
of interest are the less retained on the sorbent their
elution with a low or moderate eluting solvent
ensures their selective recovery, as the interferent
compounds will remain on the sorbent due to
stronger interactions with the solid support. In
some cases, this selectivity may authorized speciation. For example, 1 M HCOOH removed only
Se(IV) from an anion-exchange resin, leaving
Se(VI) retained on the sorbent, which was further
eluted using 2 M HCl w19x.
Finally, the elution solvent should be compatible
with the analysis technique. In particular, when
using both flame and electrothermal AAS, HNO3
should be preferred to other acids (namely
H2SO4, HCl), as nitrate ion is a more acceptable
matrix w128x.
3.2.3.2. Solvent pH. As retention of trace elements
on solid sorbents is usually pH-dependent, careful
choice of the elution solvent pH may enhance
selectivity in the SPE procedure. As an example,
once retained on eriochrome black-T (ERT)-functionalized-silica gel, Mg(II) could be eluted first
at a pH approximately 4, while increasing the pH
to 5–6 was required for eluting Zn(II) w9x.
3.2.3.3. Elution mode. Most of the time, for practical reasons, sample loading and elution steps are
performed in a similar manner. However, to avoid
irreversible adsorption and ensure quantitative
recoveries, elution in the backflush mode is recommended in some cases. This means that the
eluent is pumped through the sorbent in the opposite direction to that of the sample during the
preconcentration step. This is especially crucial
when carbon-based sorbents have to be used due
to possible irreversible adsorption of the analytes.
3.2.3.4. Solvent flow-rate. The flow-rate of the
elution solvent should be high enough to avoid
1214
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
excessive duration, and low enough to ensure
quantitative recovery of the target species. Typical
flow-rates are in the range of 0.5 to 5 mlymin for
cartridges and of 1 to 20 mlymin for disks w34x.
As a rule, the higher the flow-rate, the larger the
solvent volume required for complete elution
w119,121,129,130x.
3.2.3.5. Solvent volume. Similar to the breakthrough volume, the elution volume may be determined either experimentally or estimated
theoretically w229x. Minimum elution volume for
a cartridge is defined as 2 bed volumes of elution
solvent. Bed volume is typically 120 mly100 mg
of sorbent. For classical disks, the minimum solvent volume required is approximately 10 mlymg
of sorbent w20x. Consequently, larger elution volumes would be required for disks. The elution
volume can usually be reduced by increasing the
concentration of the eluting solvent (e.g. acid).
However, in this case, problems with subsequent
analysis may be encountered (e.g. F-AAS). Alternatively, the use of micro-sized disks may allow
reduced solvent volume w20x.
The elution step should enable sufficient time
and elution volume to permit the metallic species
to diffuse out of the solid sorbent pores. As a rule,
2 elution cycles are usually recommended as compared to a single step (e.g. 2=5 ml elution should
be preferred to a single 10 ml elution). Soaking
time is also critical and 2 to 5 min soak is most
of the time allowed before each elution.
4. Applications of SPE to the determination of
selected trace elements
4.1. Cadmium
Cadmium is known to be a highly toxic trace
metal. Owing to its very low concentrations in the
environment, a preconcentration is usually required
for its determination. This can be performed on an
anion-exchange resin, after reaction of Cd(II) with
chloride and the formation of the anionic CdCl2y
4
complex w86x. Yet, Cd(II) retention generally
occurs through chelation, either by adding a chelating agent to the sample, by impregnation of the
sorbent, or by the synthesis of new chelating resins.
Hence, a FI preconcentration on-line with F-AAS
has been reported for the determination of Cd(II)
w77x. Cadmium complexed with DDTC was sorbed
on the inner walls of a PTFE knotted reactor, and
further on-line eluted with isobutyl methyl ketone
(IBMK) giving a detection limit of 0.1 mgyl.
However, very acidic pHs (lower than 2) were
required for optimum sensitivity and collection
efficiency. In addition, DDTC is rather non-selective, so that retention of other trace elements may
occur. This drawback maybe overcome by adding
masking agents, such as thiourea and ascorbic
acidyphenanthroline for copper and iron, respectively, or by choosing a more selective reagent,
such as DDTP w233x. Still very acidic pHs were
required for optimum sensitivity and collection
efficiency. APDC offers the advantage of a broader
pH range without decomposition. Hence, Cd(II)
complexed with APDC was stable for pHs between
4 and 8, and could be efficiently retained on C18silica w56,124x. Further elution with methanol and
FI on-line ET-AAS analysis enabled detection
limits of 0.178 ngyl or 1.26 ngyl depending on
the system used. Other chelating reagents may be
used, such as PAR or PADMAP w58x, or tetra-(4bromophenyl)-porphyrin (T4BPP)w41x.
Impregnation of the sorbent with a chelating
reagent has been reported for the preconcentration
of Cd(II). In that case, the choice of a chelatant
that have a high affinity for cadmium is preferred
to ensure high selectivity. For example, BSQ has
been immobilized on Amberlite XAD-7 and used
in a FI system giving a detection limit of 1.9 mgy
l w78x. However, Zn(II) was also retained, while
other ions were found to interfere (namely Mg(II),
Cu(II), Fe(III)). Amberlite XAD-7 coated with
DMBS also enabled the retention of Cd(II) from
neutral medium with simultaneous retention of
Pb(II) w196x.
When ICP–AES is used as the analysis technique, the use of organic solvents should be
avoided as they may generate strong turbulence in
the ICP. So, new chelating resins were developed
for the Cd(II) preconcentation in a FI–ICP–AES
system, such as l,5-bis(di-2-pyridyl) methylene
dithiocarbohydrazide (DPTH)- or methylthiosalicylate (TS)-functionalized silica gel leading to
detection limits of 1.1 and 4.3 mgyl, respectively
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w51x. They offer the advantage of having no
affinity for sodium, potassium, calcium and magnesium, enabling the Cd(II) analysis in real water
samples. However, other trace elements reduced
Cd(II) retention on both resins, such as Zn(II) or
Cu(II). In some cases, the interfering effect of
Zn(II) can be avoided by careful adjustment of
the sample pH, as observed on the Lewatit
TP807’84 resin that contains a phosphonic derivative as extractant w33x. Nevertheless, other ions
were still co-extracted with Cd(II), namely Cu(II)
and Pb(II).
4.2. Chromium
Chromium species enter the environment as a
result of effluent discharge from steel industries,
electroplating, tanning industries, oxidative dyeing,
chemical industries and cooling water towers. They
may also enter drinking water supply systems from
the corrosion inhibitors used in water pipes and
containers or by contamination of the underground
water from sanitary landfill leaching. Therefore, it
is of major concern to study the characteristics of
chromium in aquatic systems. Chromium occurs
mainly in (III) and (VI) oxidation states. While
Cr(III) is an essential trace element, Cr(VI) is
highly carcinogenic and mutagenic due to its high
oxidative character. So, it is important to develop
analytical methods that enable analysis of chromium in its different oxidation states. However,
sampling and preconcentration steps might disturb
the redox equilibrium between Cr(III) and Cr(VI),
thereby affecting the original speciation state of
the sample.
Most SPE methods are based on the high reactivity of Cr(VI), due to the relatively inert nature
of Cr(III). Many methods are thus based on the
determination of Cr(VI) and total chromium. FI
on-line preconcentration procedures reported for
chromium species were exhaustively reviewed up
to 1992 by Sperling et al. w71x, and later (until
1998) by Prasada Rao et al. w59x.
4.2.1. Cr(VI)
The determination of chromium is frequently
achieved by spectrophotometry after derivatisation
with a reagent such as DPC. The reaction of DPC
1215
is very selective for Cr(VI) so it can be performed
directly without a separation step. The chromate
oxidizes DPC to diphenylcarbazone (DPCO) to
form a soluble strongly red–violet compound with
Cr(III) (Cr(III)-DPCO(3yn)q ). A large excess of
DPC is essential as compounds present in the
sample may consume the reagent. The Cr(III)DPCO complex can be retained on polyethylene
packed in a column and subsequently eluted with
methanol before being analyzed by LC w204x. This
procedure was applied to the determination of
chromium in geological samples. The determination of total chromium may also be achieved after
preliminary oxidation of Cr(III). Elements posing
interference with this method are mainly Mo(VI),
Fe(III) and V(V), and their separation using SPE
with an anionic-exchanger (SAX) has been performed for the subsequent spectrophotometric
determination of chromium w194x. The Cr(III)DPCO complex was also found to be retained on
cation-exchange (SCX) membrane disks w234x.
The color intensity of the membrane was then
correlated to the Cr(VI) concentrations by visual
analysis. This simple procedure was found to
provide a highly sensitive semi-quantitative field
test for the determination of Cr(VI) in aqueous
samples. A cation-exchange resin was also used
for the FI on-line preconcentration of the Cr(III)DPCO complex w83x, which can be retained at pH
1 on Amberlite XAD-16 resin and then eluted
using 0.05 M H2SO4 solution in methanol w161x.
In this way, Cr(VI) can be determined in tap water
samples, as total chromium after oxidation of
Cr(III) into Cr(VI) using potassium permanganate.
Cr(VI) may also be chelated by DDTC, and
subsequently retained on C18-silica w60x. Total
chromium may be estimated using the same procedure with prior oxidation of Cr(III) to Cr(VI).
The FI on-line preconcentration systems enabled
detection limits of 16 ngyl for Cr(VI) and 18 ngy
l for total Cr. Very recently, selective retention of
Cr(VI), compared to Cr(III) was obtained using
PTFE turnings packed in the micro-column of a
FI manifold. APDC was used for complexation of
Cr(VI) in the samples before preconcentration,
and elution was achieved with IBMK before analysis using F-AAS w49x. Similarly, after reaction
with APDC, the Cr(VI) complex could be retained
1216
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
on the PTFE inner wall of a knotted reactor or on
PTFE beads packed into a column, and subsequently eluted with ethanol w74,75x. Also, acidic
alumina enables selective retention of Cr(VI) w70x
and a micro-column was used in a FI manifold to
separate and preconcentrate Cr(VI) from Cr(III)
in water samples. However, it was later reported
that between pH 3 and 6 Cr(III) could also be
retained on that sorbent w235x.
4.2.2. Cr(III)
Very recently, selective preconcentration of
Cr(III) on a cellulose micro-column has been
reported to be highly dependent on sample pH
w183x. Below pH 8, very low retention occurred,
while at pH 11 almost quantitative adsorption
could be achieved. Elution of the retained Cr(III)
species with 5 ml of HCl (2 M) enabled its
subsequent determination by ET-AAS with a 1.8
ngyl limit of detection. This method also enabled
the determination of total chromium following
initial reduction of Cr(VI) to Cr(III) with
hydroxylamine.
The coating of the positively charged acidic
alumina with an anionic surfactant, SDS, has been
reported to enable selective retention of Cr(VI) in
strongly acidic solution, while the cationic Cr(III)
remains unabsorbed w151x. Separation of the two
species could thus be obtained and Cr(III) determined by ET-AAS. However, this method presents
two major limitations; no analyte enrichment and
the need to adjust sample pH to 0.6, which may
affect chromium speciation. In another study, basic
alumina has been shown to selectively retain
Cr(III) at pH 2–7 w73x, permitting elution with
nitric acid.
Selective retention of Cr(III) was also reported
with a macroporous PS-DVB resin (CHP-20P)
after complexation in solution with 8-HQ at 85 8C
w159x. The use of hydroxylamine as a reductant
was found efficient for the reduction of Cr(VI) to
Cr(III) without affecting Cr(III) retention as it
does not complex this species. 8-HQ-immobilizedpolyacrylonitrile fiber has been recently reported
to selectively retain Cr(III) at pH 6, enabling its
preconcentration from river and reservoir water
samples, while Cr(VI) was unretained w186x.
Selective retention of Cr(III) (cationic) was also
achieved on a chelating ion-exchange column
packed with poly(aminophosphonic acid) (PaPhA)
resin w81x. By using on-line FI preconcentration
coupled to F-AAS, a detection limit of 0.2 mgyl
could be obtained with a sample throughput of 30
hy1.
4.2.3. Cr(VI)yCr(III)
A procedure based on the reaction of chromium
species with APDC and subsequent retention of
the complexes on SPE permitted a subsequent online LC–UV analysis w39x. The Cr(III) reacts with
the chelating agent under relatively mild conditions
to give only one product, i.e. triswpyrrolidine-ldithioato-S,S9xchromium(III), whereas Cr(VI)
reacts to give two products, one being the former
complex. Thus, the concentration of Cr(VI) needs
to be corrected for the Cr(III) complex. The
automated SPE system was optimized to yield
detection limits of 0.2 mgyl for Cr(III) and 0.06
mgyl for Cr(VI). A FI on-line preconcentrarion
procedure followed by F-AAS detection has been
reported to allow determination of both chromium
species in water samples based on selective formation of DDTC complexes of Cr(VI) in the pH
range of 1–2, and of Cr(III) in the 4–9 pH range
w59x. A detection limit of 0.02 mgyl could thus be
achieved. Cr(III) could also be retained in the
presence of Mn(II), which enhances the Cr(III)
signal w59x.
TiO2 has been recently reported to be very
promising for chromium speciation w108x. Indeed,
this sorbent can selectively adsorb Cr(III) or
Cr(VI) depending on the pH of the sample. At pH
2, Cr(VI) is the sole chromium species retained,
while at pH 8 it is Cr(III). Nitric acid (0.5 or 1
M) allows quantitative elution of the retained
species. Acidic alumina has also been reported to
retain both Cr(III) and Cr(VI) w235x. However,
careful adjustment of the pH was of prime importance as below pH 3 and above pH 6 retention of
Cr(III) and Cr(VI), respectively, decreased w235x.
Hence, a FI on-line preconcentration method has
been reported on activated acidic alumina with
buffering of the sample before retention either at
pH 7 (for Cr(III)) or pH 2 (for Cr(VI)) w71x.
Cr(III) exhibited a typical cationic sorption (it
increased with pH and decreased when competing
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
cations are present), whereas Cr(VI) exhibited a
typical anionic sorption (it decreased with increasing pH and in the presence of competing dissolved
anions). Thus, the use of neutral alumina seems
more appropriate for chromium speciation since it
offers the advantage of requiring no adjustment of
the water sample pH. Hence, both Cr(III) and
Cr(VI) can be quantitatively retained on neutral
alumina with speciation being achieved using
selective elution of the species, i.e. 1 M ammonia
solution for Cr(VI) followed by 4 M HNO3 for
Cr(III) w110x. This method affords a 25-fold preconcentration factor with a limit of detection of
10 ngyl. A similar preconcentration on alumina
followed by selective elution for separation of the
two chromium species has been reported w72x.
A new resin that consists of PS-DVB functionalized with NDSA enabled the retention of Cr(VI)
at sample pH of 1.5, and of Cr(III) at pH 6.5
w181x. Thus, speciation of chromium was accomplished by adjustment of the pH along with the
percolation of two sub-samples at the desired pH.
The selective retention of both chromium species
could also be achieved on a polymeric sorbent
containing aminocarboxylic groups at pH 3 and 7,
for Cr(VI) and Cr(III), respectively w236x. Microwave heating was found to promote the sorption.
Chromium species may also be retained on an
anionic-exchanger (SAX) after their complexation
with EDTA w237x. Controlled elution of the analytes with 0.5 M NaCl enables their speciation. In
this manner, detection limits of 0.4 and 1.1 mgyl
were obtained for Cr(III) and Cr(VI), respectively.
4.3. Iron
Iron is widely distributed in nature and is one
of the most important elements in biological systems. Its biological effectiveness is influenced by
its chemical properties, such as valence, solubility
and the degree of chelation or complex formation.
Several methods have been proposed for the determination of Fe(III) and Fe(II) species.
4.3.1. Fe(III)
Some solid phases have been synthesized to
enable high selectivity towards Fe(III). Thus, the
chemical bonding of formylsalicylic acid on ami-
1217
no-silica gel enabled the preconcentration of
Fe(III) from a mixture containing other trace
elements in batch experiments w35x. The capacity
of this sorbent for Fe(III) was 0.95 mmolyg. This
high selectivity was attributed to the presence of
two chelating oxygen atoms. The selective SPE of
Fe(III) on purpurogallin chemically immobilized
on silica gel has also been reported w140x. Once
eluted from the sorbent the iron species were
analyzed using AAS. Due to strong affinity of
Fe(III) to the bound organic compound, as compared to Fe(II) (the distribution coefficient, Kd,
was found to be 120 500 for Fe(III) and 12 700
for Fe(II)), speciation of iron could be achieved
using this procedure. Only minor Fe(III) (2.1%)
was found to be reduced to Fe(II) upon interaction
with the sorbent. Using batch experiments, Fe(III)
could be selectively extracted from tap water as
well as from a soft drink sample (7-Up).
Yamini and Amiri w117x developed an efficient
method for the selective extraction, concentration
and determination of trace amounts of Fe(III) in
aqueous media, enabling determination of iron in
a 500 ml water sample in less than 30 min with a
reproducibility better than 3%. Iron(III) was initially reduced to Fe(II) by addition of hydroxylamine (NH2OH) and the bathophenanthroline
complex Fe(bathophenanthroline)2q
was analyzed
3
by the use of C18-silica membrane disks and
spectrophotometry. The ligand was added to the
sample before SPE, and the solution heated to
enhance formation of the complex. By comparison
with AAS and ICP emission spectrometry, this
method offers simplicity and applicability to field
determination of iron. However, pure solvents
eluted only a fraction of the complex and addition
of NaClO4 to the elution solvent was required for
complete removal of the retained complex, indicating that interactions between the complex and
the C18-silica are dispersive or ionic. At sample
pH below 2.5 recovery decreased probably due to
competition of Hq with Fe(II) for reaction with
bathophenanthroline. The influence of several ions
was investigated, most were tolerated at high levels
without interfering with the determination of iron.
However, some species such as Co2q, Ni2q,
2q
VOy
, interfered. The inter3 and especially Cu
2q
ference effect of Cu is due to the preferential
1218
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
formation of a very stable, almost colorless, complex between Cu(I) and bathophenanthroline. Its
effect was eliminated by the addition of excess
amounts of thiourea, as a masking agent, while
the effect of the other ions was eliminated by use
of excess amounts of bathophenanthroline. A FI
catalytic spectrophotometric method has also been
developed for the shipboard determination of iron
in sea water samples w52x. Retention was achieved
using 8-HQ-functionalized silica gel. After elution
with HCl mixing with the reagents (H2O2 and
N,N-dimethyl-p-phenylenediamine (DPD)) was
performed to ensure the formation of the color. A
detection limit of 0.016 nM could thus be
achieved.
4.3.2. Fe(II)
Iron(II) is thermodynamically unstable in sea
water containing dissolved oxygen due to its rapid
oxidation to Fe(III) (half-life being approx. 4–10
min depending on the pH). Yet, the determination
of Fe(II) in sea water is important because of its
role in the solubility, speciation and biological
utilization of iron in oceanic surface waters; in
addition Fe(II) may reduce oxygen, thereby producing radicals in the water.
The colorimetric reagent ferrozine (FZ) w3(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)l,2,4-triazinex forms a stable, colored complex with Fe(II)
in a pH range of 4–10, but not with Fe(III) w238x.
Interferences are also possible due to complexation
of Cu(I), and to a lesser extent of Co(II) and
Ni(II) by FZ. Thus, a procedure has been developed enabling the preconcentration of Fe(II) from
sea water, thanks to its retention as the Fe(FZ)3
complex on a C18-silica cartridge and subsequent
elution with methanol w122x. Iron was then analyzed directly by spectrophotometry (562 nm).
C18-silica was loaded with FZ by passing a FZ
solution through the cartridge (the retention capacity of the cartridge for FZ increased with increasing
ionic strength of the solution). Once the sea water
has been passed through the cartridge, washing
was performed with 5 ml of 0.1 M NaCl–0.005
M NaHCO3 to remove sea salts and prevent
precipitation of Mg2qand Ca2q in methanol upon
elution. Cu(I) interference was minimised by adding neocuproine (NCH) to the methanol extract
avoiding the presence of the Cu(FZ)2 complex.
However, in this method both the Fe(FZ)3 complex
and the excess FZ were eluted and contributed to
the absorbance measurement, which may result in
unreliable determination of low Fe(II) concentrations. Therefore, this procedure was further
improved by performing a chromatographic separation of the two species after the SPE step. In
addition, 254 nm was found more suitable for
detection than 562 nm. In this way, ultratrace
amounts of Fe(II) could be determined in several
samples (aerosols, rainwater and sea water) w123x.
A procedure, similar to that reported by King et
al. w122x has been used for the on-line FI preconcentration of Fe(II) from sea water samples w68x.
It could be extended to Fe(III) determination based
on its initial reduction by addition of ascorbic acid
to the sample. Copper interference could be suppressed by loading the C18-silica with a mixture
of FZ and NCH, but at the same time the column
capacity was lower than when loaded with FZ
alone.
4.3.3. Fe(III)yFe(II)
Most of the methods report the determination of
only one of the two iron species mainly by
selective complexation. However, this can cause a
shift in the Fe(II)yFe(III) equilibrium in the solution as a result of redox reactions. To prevent such
problems, a procedure has been reported that
enables the simultaneous complexation of both
Fe(II) and Fe(III) in the sample followed by
retention of the complexes on selective solid sorbents w18x. Fe(II) was complexed by addition of
1,10-phenanthroline, while Fe(III) formed a complex with ferron (8-hydroxy-7-iodoquinoline-5-sulfonic acid). The solution was thus passed
successively to an anion-exchange resin and a
reversed-phase sorbent. Since the Fe(III)-ferron
complex is negatively charged, it was retained by
the first solid phase (for sample pH 3–6), while
the Fe(II)-phenanthroline was passed through due
to its non-polar character. This complex was then
retained by the second solid sorbent (C18-silica).
This method enabled the determination of both
labile Fe(II) and Fe(III) species in wine samples.
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
4.4. Lead
Lead is a toxic metal, which accumulates in the
vital organs of man and animals. Its cumulative
poisoning effects are serious haematological damage, anemia, kidney malfunctioning, brain damage,
etc. Lead is still emitted into the biosphere in
considerable amounts owing to its application as a
fuel additive, mainly as tetraethyllead and tetramethyllead. It is also present in many industrial
streams. Due to the presence of lead in environmental samples at low levels, its separation from
other elements present and the use of a preconcentration step prior to lead determination are usually
necessary. All the studies reported until now
focused on the preconcentration of inorganic lead
Pb(II). The performances of Pb determination
using different sorbent materials have been
reviewed recently w50,176x. Some examples are
given below. Firstly, as a cationic species, Pb(II)
can be retained on cation-exchangers, such as basic
alumina w239x. However, such sorbents are rather
non-selective. So, other strategies have been used
that are the retention of Pb complexes on hydrophobic sorbents, the retention of Pb(II) on sorbents
coated with a chelating reagent and the synthesis
of new chelating resins.
Lead complexed with DDTP could be retained
on C18-silica, activated carbon and PUF w63x. In
that way analysis through a FI system coupled to
F-AAS was performed with limits of detection of
0.3, 1.2 and 3 mgyl for C18-silica, PUF and
activated carbon, respectively. In another FI system
Pb(II) was complexed with APDC retained on
PTFE turnings and further eluted with IBMK
leading to 0.8 mgyl as a limit of detection w50x.
This method enabled the determination of Pb(II)
in various environmental and biological samples.
Complexes can be formed with DDTC in acidic
medium, further retained on C18-silica and eluted
with IBMK or methanol before F-AAS, enabling
the detection of 3 to 10 mgyl w62,233x. Alternatively, the sorbent can be impregnated with the
chelating reagent. Hence, the SPE of lead on C18silica disks has been reported after impregnation
of the sorbent with a S-containing Schiff’s base to
enable Pb(II) chelation w120x. After elution with
nitric acid lead was further analyzed by F-AAS
1219
with a limit of detection of 16.7 myl. Retention of
lead was quite selective even in the presence of
other ions. The addition to the sample of ammonia
as a masking agent was recommended to suppress
the interfering effect of some cations, namely
Cu(II), Zn(II) and Hg(II). Similarly, the coating
of C18-silica with BAS was found highly selective
in retaining Pb(II) with subsequent elution using
acetic acid and F-AAS analysis leading to 50 ngy
l as a limit of detection w121x. Pb(II) could also
be retained on Amberlite XAD-7 coated with
DMBS w196x or XO w176x, Amberlite IRA-904
impregnated with TCPP w8x, or PUF coated with
2-(2-benzothiazolylazo)-2-p-cresol w240x.
Chelating resins have also been synthetized for
the selective preconcentration of Pb(II). For example, Amberlite XAD-2 was functionalized through
an azo spacer by several chelating agents, such as
CA, PC and TSA, and used for the retention of
Pb(II) from water samples w176x. Similarly, this
sorbent functionalized with SA also enabled the
retention of Pb(II), along with Zn(II) w171x. In
each case nitric acid enabled lead desorption.
Limits of detection in the 2.4–4.9 mgyl range were
obtained. Amberlite XAD-7 functionalized with a
crown ether was also found suitable for the preconcentration of Pb(II) w241x.
Very recently, an attractive test procedure has
been reported that enables the determination of as
low as 20 ngyl of Pb(II) w203x. It is based on the
immobilization of an enzyme, alkaline phosphatase
on PUF.
4.5. Mercury
The presence of mercury species in aquatic food
chain is of great concern as it is well-known that
inorganic mercury (Hg2q) is converted into highly
toxic methylmercury (MeHgq) by aquatic organisms. Due to the presence of mercury in environmental samples at low levels, its separation from
other elements present and the use of a preconcentration step prior to the determination is
usually necessary.
4.5.1. Hg(II)
Mercury can be preconcentrated from aqueous
samples using a chelating ion-exchange resin con-
1220
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
taining histidine covalently bound to its carboxyl
group w242x. A chelating PS-DVB-based resin with
picolinic acid amide (PAA) as the functional group
was also found efficient for Hg(II) retention from
water samples w184x. Several functional groups
chemically bound to silica gel have also been
reported to afford selective sorbents for preconcentration of Hg(II) during adsorption. This was the
case with DZ w104x and dithioacetal derivatives
w105x. Another procedure involving the use of
C18-silica disks impregnated with hexathia-18crown-6-tetraone (HT18C6TO), was shown to
quantitatively extract Hg(II) from natural waters
in less than 15 min w130x. Recovery was nearly
independent of pH (in the range of 1 to 7) as
already reported for the solvent extraction of metals with crown ethers. Before eluting Hg2q with 1
M HBr, a washing step with 1 M HNO3 was
recommended to remove small amounts of retained
Cu2q, Zn2q, Pb2q and Cd2q.
4.5.2. Hg(II)yorganic Hg
A chelating resin based on vinyl polymer and
containing dithiocarbamate groups was found efficient for retention of inorganic and organic mercury from water samples over a broad range of
pHs (1 to 11) w189x. The species were eluted
using an acidic aqueous solution of 5% (wyv)
thiourea, enabling a preconcentration factor of 666
and the determination of mercuric species with a
limit of detection of 0.2 ngyl. The use of another
chelating resin containing dithiocarbamate groups
was also found effective in retaining inorganic as
well as organic mercury in the pH range 1–4
resulting in limit of detection of 0.5 ngyl w243x.
The on-line FI preconcentration of mercury species
(Hg(II), methylmercury, ethylmercury) on a
dithiocarbamate resin has also been reported w244x.
Detection limits of 0.05 ngyl and 0.15 ngyl for
organic and inorganic mercury, respectively, could
be obtained. However, this method involved manual steps once the species were eluted with thiourea, extraction into toluene as the diethyl
dithiocarbamate complexes, butylation with a Grignard reagent and subsequent gas chromatography
(GC) analysis. In addition, preconcentration failed
in the presence of high amounts of humic substances in the water samples.
Complexation of mercuric species with APDC,
FI on-line preconcentration on C18-silica, further
separation with LC, and analysis by CV-AAS has
been reported w43x. In this manner, Hg species
(methylmercury, ethylmercury, phenylmercury and
Hg(II)) in fish and human urine could be analyzed
at the ngyl level. Chelation with DDTP and preconcentration on C18-silica in a FI–CV-AAS system resulted in detection limits of 10 ngyl for
methylmercury and Hg(II) with an enrichment
factor of 20 w64x. Several ligands were tested:
DDTC, APDC and DZ (or diphenylthiocarbamate)
w55x. Results showed the superiority of carbamate
type reagents for the preconcentration of Hg(II)
and methylmercury using this system. With
DDTC, detection limits of 16 ngyl of Hg could be
obtained.
4.6. Selenium
Selenium is present in the environment from
both natural and anthropogenic inputs. This element has been recognized as an essential nutrient.
However, at concentrations higher than 130 mgyl
it becomes toxic. Se(IV) and Se(VI) are the
predominant species in natural waters. Biomethylation may also occur, leading to the formation of
organic species such as dimethyl selenide (DMSe),
dimethyl diselenide (DMDSe) and diethyl selenide
(DESe), and detoxification. Therefore, a reliable
speciation procedure is required to evaluate toxicity of samples. An overview of SPE procedures
developed for selenium has been recently given
w193x and some are detailed below. It appears that
most methods were dedicated to the determination
of inorganic selenium.
4.6.1. Se(IV)
APDC has been loaded on C18-silica and used
for the preconcentration of Se from sea water prior
to ET-AAS w114x. Speciation of inorganic Se(IV)
and Se(VI) was possible since APDC selectively
chelates Se(IV). A reduction of Se(VI) to Se(IV)
prior to chelation is required for the determination
of total inorganic Se. However, this method was
not selective as other trace elements were retained
on the sorbent (such as Bi, Pb, Zn, As, Sn, V).
Complexation of Se(IV) could also be obtained
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
with
3-phenyl-5-mercapto-1,3,4-thiadiazole-2(3H)-thione (Bismuthiol II), which was then
retained on activated carbon in batch experiments
w222x. Se(IV) could also be retained on Chelex100 (in the iron form) over a wide pH range (up
to 10) w245x.
4.6.2. Se(IV)ySe(VI)
Both forms of inorganic selenium can be
retained on acidic alumina and extracted from
natural waters without any pH adjustment w111x.
Selective elution is achieved using ammonia at
different concentrations for eluting Se(VI) and
then Se(IV) enabling speciation of inorganic selenium in natural waters. Quantitative recoveries
from spiked tap water and ground water were
obtained except for one tap water, where 42 and
154% of Se(IV) and Se(VI), respectively, were
recovered possibly due to oxidation of Se(IV) by
residual chlorine. Similar observations were made
in another study w40x.
Dowex-lX8 ion-exchanger enabled preconcentration of both Se(IV) and Se(VI) w246x. The
species were then separated during elution with
two different concentrations of HCl. Inorganic
selenium species were also retained on several
anion-exchange resins based on either cellulose or
PS-DVB copolymer w225x. Despite a lower affinity,
the functionalized cellulose sorbent was preferred,
as it enabled a better separation of Se(IV) and
Se(VI) during elution with different concentrations
of nitric acid. Traces of Se(IV) and Se(VI) could
also be retained on a molybdate-form anionexchange resin in batch experiments w247x, permitting speciation of inorganic selenium in natural
waters except sea water (where foreign ions
interfered).
The coupling of SPE to LC–ICP–MS enabled
the speciation of inorganic selenium in natural
water samples by ion-pairing (with tetrabutylammonium phosphate as the reagent) and sorption on
C18-silica, subsequent elution and separation in the
chromatographic column by anion-exchange w40x.
However, sample volumes were limited to 10 ml
due to the limited capacity of the preconcentration
column.
1221
4.6.3. Organic Se
Tanzer and Heumann w248x developed a method
for the selective determination of acidicyneutral
and basic organoselenium species in water samples
based on the selective retention of the species on
Amberlite XAD-2 at different sample pHs (3 and
8, respectively). However, this method was found
questionable by other authors who noted partial
retention of Se(IV) on that sorbent w225x.
4.6.4. Se(IV)ySe(VI)yorganic Se
Simultaneous preconcentration of inorganic and
organic selenium species is a more difficult task.
A combined SPE method has been reported to
enable preconcentration of both inorganic and
organic species of selenium w19x. An anionexchanger cartridge was placed on the top of a
C18-silica cartridge so that inorganic selenium was
retained on the first cartridge, while organic species were retained on the reversed-phase sorbent.
The cartridges were then separated and the species
eluted: 1 M HCOOH for Se(IV), 3 M HCl for
Se(VI), CS2 for organic compounds. In another
recent procedure, simultaneous determination of
organic (selenocystine) and inorganic selenium
(Se(IV) and Se(VI)) species was achieved using
off-line preconcentration on Amberlite IRA-743
followed by separation of the species and analysis
using LC–ICP–MS w193x. No adjustment of the
sample pH was required. However, the sorbent
was not selenium selective, and selenomethionine
could not be retained under the conditions developed due to strong competition with hydrogen
carbonate.
4.7. Tin
Organotin compounds have found widespread
industrial applications as biocides, antifouling
paints, catalysts and polyvinyl chloride stabilizers.
So, there are a variety of pathways for their entry
into the environment. Whereas inorganic tin is
basically harmless, some organotin compounds are
highly toxic, especially tri-substituted organotin
species. Therefore, there is a need for sensitive
methods that enable the determination and speci-
1222
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
ation of these compounds. Several studies report
the use of SPE for organotin determination w249–
251x.
4.7.1. Butyltins
Tributyltins have been used as insecticides, fungicides, acaricides and preservatives for many
different types of materials. In particular, they have
been used as antifouling paints (as biocides) on
ships, boats and dock resulting in release of TBTs
directly into the aquatic environment where they
are non-specific and extremely toxic to non-target
animal and plants species. C18-silica, either in
cartridges or in PTFE disks, has been found
effective in preconcentrating TBTs from aqueous
solutions w24x. Enrichment factors up to 1000 can
be obtained enabling the quantification of TBTs at
the 0.1 mgyl level. In addition, TBTs can be stored
on such solid supports at room temperature for at
least 1 month. Amberlite XAD-2 impregnated with
tropolone has also been reported to retain TBT
and dibutyltin, while monobutyltin was not
retained w164x. The addition of 0.8% sulfuric acid
to the water sample enabled the selective retention
of only TBT on the resin. This species was
subsequently eluted with IBMK and analyzed by
ET-AAS enabling quantitative determination of
TBT in water samples with a limit of detection of
14.4 ngyl and a preconcentration factor of 80.
4.7.2. Phenyltins
Triphenyltin is retained on C18-silica cartridges,
even though a fraction of the compound cannot be
recovered w112x. Hence, best recoveries (between
81 and 89%) were obtained by elution in the
backflush mode with 10y4 M 3-hydroxyflavone in
methanol. Retention of TPhT on other silica-based
sorbents (octyl, phenyl and cyanopropyl) has also
been reported w112x.
4.7.3. Butyltinsyphenyltins
A semi-automated system was reported that
enabled organotin speciation w251x, wherein preconcentration was performed using a microcolumn
of C18-silica placed in a FI manifold. Percolation
of a derivatising reagent (sodium tetraethylborate)
through the column enabled derivatisation of the
organotin compounds. Elution of the derivatised
species (monobutyltin, monophenyltin, dibutyltin,
diphenyltin, TBT and TPhT) was achieved using
methanol and their separation and analysis was
performed using GC–AES. In this manner, with
rather small sample volumes (10–50 ml) detection
limits in the range of 0.10–0.17 ngyl could be
obtained. Application of the method was tested
with real river water samples, and results were
consistent with those obtained using classical liquid–liquid extraction. Similarly, in an off-line system,
organotins
derivatised
by
sodium
tetraethylborate could be retained on C18-silica
disks, and further eluted with supercritical CO2
w252x.
The use of tropolone-loaded C18-silica has also
been used for the retention of several butyltins and
phenyltins (mono-, di-, tri- and some tetra-substituted compounds) w118x. However, selectivity
could not be achieved using SPE only. Organotins
were separated by subsequent GC analysis after
their ethylation with Grignard reagent. This method affords a sensitivity of low ngyl in surface
waters and mgykg in sewage sludges.
Speciation of tin has also been reported using
both graphitized carbon black and silica gel as
sorbents w223x. Water samples were first passed
through GCB, allowing the retention of TBT and
TPhT, while inorganic tin passed unimpeded and
was analyzed directly. The organic species were
subsequently eluted with a mixture of methanoly
dichloromethane (4:1), and separated on silica gel.
The overall method provided an enrichment factor
of up to 80 000, but required the complete evaporation of the organotin fraction eluted from GCB,
and the dissolution of the solid residue in hexane
before separation on silica gel.
Finally, organotins can be efficiently retained on
strong cation-exchange silica-based bonded phases
(Bond-Elut SCX) and strong cation-exchange
polymeric-based phase (Oasis-MCX). The presence of NHq
was essential for elution of the
4
compounds. Recoveries were lower with the polymeric phase particularly for TPhT, probably
because of strong interaction of the aromatic rings
with the N-vinylpyrrolidone-divinylbenzene support w36x.
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
5. Conclusion
The use of SPE procedures has been growing in
the past few years due to their advantages offered
for trace element determinations, namely conservation of species, good preconcentration factors
(thus enabling the achievement of very low limits
of detection), ease of automation, and possible online coupling to instrumental techniques.
Despite the numerous steps and parameters used
to enable efficient extraction and recovery of the
target analytes, the choice of the solid sorbent is
the most critical step. Among the numerous sorbents that have been used, it clearly appears that
the initial use of ion-exchangers is being replaced
by more selective supports containing chelating
functional groups. Such sorbents are frequently
based on hydrophobic supports namely C18-silica
or PS-DVB copolymer, the latter affording a broader pH range. The simplest procedure consists of
adding the chelating reagent directly to the sample.
A more suitable way of proceeding is to load the
reagent on the solid sorbent. The coated sorbent
thus obtained may usually be used several times,
but partial leaching of the chelating agent may
occur over time during elution of the analytes,
{
especially if the eluting solvent is too concentrated.
Alternatively, the reagent may also be chemically
bound to the sorbent leading to the synthesis of
new phases, and thus avoiding any leaching of the
reagent. Promising results have also been recently
obtained with inorganic oxides such as titania and
alumina, as retention of some trace elements could
be achieved with the raw sample (i.e. no reagent
addition nor pH adjustment), thereby avoiding
possible speciation changes in the sample.
Examples given in this review for several trace
elements show the high potential of SPE, especially its possible high selectivity (by choosing the
nature of the sorbent andyor the chelating agent,
as well as the nature of the eluent). In fact, in
some cases, differentiation of species may be
achieved, thereby offering new opportunities for
speciation. There is thus no doubt that this technique will face a growing interest for trace element
determination and speciation in the future, as
already evidenced for organic micropollutant determinations in the recent years.
1223
References
w1x I. Liska, Fifty years of solid-phase extraction in water
analysis-historical development and overview, J. Chromatogr. A 885 (2000) 3.
w2x C.F. Poole, Solid-phase extraction, Encyclopedia of
Separation Science, 3, Academic Press, 2000, p. 1405.
w3x M.C. Hennion, Sample handling strategies for the analysis of non-volatile organic compounds from environmental water samples, Trends Anal. Chem. 10 (1991)
317.
w4x J.L. Lundgren, A.A. Schilt, Analytical studies and applications of ferroin type chromogens immobilized by
adsorption on a styrene-divinylbenzene copolymer,
Anal. Chem. 49 (1977) 974.
w5x M. Chikuma, M. Nakayama, T. Itoh, H. Tanaka, K. Itoh,
Chelate-forming resins prepared by modification of
anion-exchange resins, Talanta 27 (1980) 807.
w6x H. Akaiwa, H. Kawamoto, K. Ogura, Kinetic studies of
ion-exchange of cobalt(II) and nickel(II) on a resin
loaded with 5-sulfo-8-quinolinol, Talanta 28 (1981) 337.
w7x K.S. Lee, W. Lee, D.W. Lee, Selective separation of
metal ions by a chelating agent-loaded anion exchanger,
Anal. Chem. 50 (1978) 255.
w8x K. Kilian, K. Pyrzynska, Preconcentration of metal ions
on porphyrin-modified sorbents as pretreatment step in
AAS determination, Fresenius J. Anal. Chem. 371
(2001) 1076.
w9x M.E. Mahmoud, Silica gel-immobilized Eriochrome
black-T as a potential solid phase extractor for zinc(II)
and magnesium(II) from calcium(II), Talanta 45 (1997)
309.
w10x M. Pesavento, R. Biesuz, M. Gallorini, A. Profumo,
Sorption mechanism of trace amounts of divalent metal
ions on a chelating resin containing iminodiacetate
groups, Anal. Chem. 65 (1993) 2522.
w11x M. Pesavento, R. Biesuz, J.L. Cortina, Sorption of metal
ions on a weak acid cation-exchange resin containing
carboxylic groups, Anal. Chim. Acta 298 (1994) 225.
w12x H. Kumagai, Y. Inoue, T. Yokoyama, T.M. Suzuki, T.
Suzuki, Chromatographic selectivity of rare earth elements on iminodiacetate-type chelating resins having
spacer arms of different lengths: importance of steric
flexibility of functional group in a polymer chelating
resin, Anal. Chem. 70 (1998) 4070.
w13x J. Seneviratne, J.A. Cox, Sol–gel materials for the solid
phase extraction of metals from aqueous solution, Talanta 52 (2000) 801.
w14x M.C. Carson, Ion-pair solid-phase extraction, J. Chromatogr. A 885 (2000) 343.
w15x V. Porta, E. Mentasti, C. Sarzanini, M.C. Gennaro, Ionpair liquid–solid extraction for the preconcentration of
trace metal ions, Talanta 35 (1988) 167.
w16x P. Janos, K. Stulik, V. Pacakova, An ion-exchange
separation of metal cations on a C-18 column coated
with dodecylsulfate, Talanta 39 (1992) 29.
1224
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w17x R. Van Grieken, Preconcentration methods for the analysis of water by X-ray spectrometric techniques, Anal.
Chim. Acta 143 (1982) 3.
w18x A.B. Tawali, G. Schwedt, Combination of solid phase
extraction and flame atomic absorption spectrometry for
differentiated analysis of labile iron(II) and iron(III)
species, Fresenius J. Anal. Chem. 357 (1997) 50.
w19x J.L. Gomez-Ariza, J.A. Pozas, I. Giraldez, E. Morales,
Use of solid phase extraction for speciation of selenium
compounds in aqueous environmental samples, Analyst
124 (1999) 75.
w20x E.M. Thurman, K. Snavely, Advances in solid-phase
extraction disks for environmental chemistry, Trends
Anal. Chem. 19 (2000) 18.
w21x C.F. Poole, Solid-phase extraction with disks, Encyclopedia of Separation Science, 9, Academic Press, 2000,
p. 4141.
w22x M. Kumar, D.P.S. Rathore, A.K. Singh, Quinalizarin
anchored on Amberlite XAD-2. A new matrix for solidphase extraction of metal ions for flame atomic absorption spectrometric determination, Fresenius J. Anal.
Chem. 370 (2001) 377.
w23x G.A. Junk, M.J. Avery, J.J. Richard, Interferences in
solid-phase extraction using C-18 bonded porous silica
cartridges, Anal. Chem. 60 (1988) 1347.
w24x O. Evans, B.J. Jacobs, A.L. Cohen, Liquid–solid extraction of tributyltin from marine sediments, Analyst 116
(1991) 15.
w25x D.F. Hagen, C.G. Markell, G.A. Schmitt, D.D. Blevins,
Membrane approach to solid-phase extractions, Anal.
Chim. Acta 236 (1990) 157.
w26x D.T. Rossi, N. Zhang, Automating solid-phase extraction: current aspects and future prospects, J. Chromatogr.
A 885 (2000) 97.
w27x L.B. Bjorklund,
¨
G.M. Morrison, Determination of copper speciation in freshwater samples through SPEspectrophotometry, Anal. Chim. Acta 343 (1997) 259.
w28x R.E. Majors, Sample preparation for HPLC and gas
chromatography using solid-phase extraction, LG-GC 4
(1989) 972.
w29x R.E. Sturgeon, S.S. Berman, A. Desaulniers, D.S. Russell, Pre-concentration of trace metals from sea-water
for determination by graphite-fumace atomic-absorption
spectrometry, Talanta 27 (1980) 85.
w30x T.M. Florence, G.E. Batley, Trace metals species in seawater-I. Removal of trace metals from sea-water by a
chelating resin, Talanta 23 (1976) 179.
w31x D.M. Sanchez, R. Martin, R. Morante, J. Marin, M.L.
Munuera, Preconcentration speciation method for mercury compounds in water samples using solid phase
extraction followed by reversed phase high performance
liquid chromatography, Talanta 52 (2000) 671.
w32x M.C. Yebra, N. Carro, M.F. Enriquez, A. Moreno-Cid,
A. Garcia, Field sample pre-concentration of copper in
sea water using chelating minicolumns subsequently
incorporated on a flow-injection-flame atomic absorption spectrometry system, Analyst 126 (2001) 933.
w33x E. Castillo, J.-L. Cortina, J.-L. Beltran, M.-D. Prat, M.
Granados, Simultaneous determination of Cd(II), Cu(II)
and Pb(II) in surface waters by solid phase extraction
and flow injection analysis with spectrophotometric
detection, Analyst 126 (2001) 1149.
w34x M. Shamsipur, A.R. Ghiasvand, H. Sharghi, H. Naeimi,
Solid phase extraction of ultra trace copper(II) using
octadecyl silica membrane disks modified by a naphthol-derivative Schiff’s base, Anal. Chim. Acta 408
(2000) 271.
w35x M.E. Mahmoud, E.M. Soliman, Silica-immobilized formylsalicylic acid as a selective phase for the extraction
of iron(III), Talanta 44 (1997) 15.
w36x E. Gonzalez-Toledo, M. Benzi, R. Compano, M. Granados, M.D. Prat, Speciation of organotin compounds
in shellfish by liquid chromatography–fluorimetric
detection, Anal. Chim. Acta 443 (2001) 183.
w37x O. Keil, J. Dahmen, D.A. Volmer, Automated matrix
separation and preconcentration for the trace level determination of metal impurities in ultrapure inorganic salts
by high-resolution ICP–MS, Fresenius J. Anal. Chem.
364 (1999) 694.
w38x J.F. Tyson, Flow injection atomic spectrometry, Spectrochim. Acta Rev. 14 (1991) 169.
w39x M. Bittner, J.A.C. Broekaert, Speciation of chromium
by solid-phase extraction coupled to reversed-phase
liquid chromatography with UV detection, Anal. Chim.
Acta 364 (1998) 31.
w40x Y. Cai, M. Cabanas, J.L. Fenandez-Turiel, M. Abalos,
J.M. Bayona, On-line preconcentration of selenium(IV)
and selenium(VI) in aqueous matrices followed by
liquid chromatography-inductively coupled plasma mass
spectrometry determination, Anal. Chim. Acta 314
(1995) 183.
w41x Q. Hu, G. Yang, J. Yin, Y. Yao, Determination of trace
lead, cadmium and mercury by on-line column enrichment followed by RP-HPLC as metal-tetra-(4-bromophenyl)-porphyrin chelates, Talanta 57 (2002) 751.
w42x B.W. Wenclawiak, T. Hees, C.E. Zoller,
¨
H.-P. Kabus,
Rhodium and palladium b-diketonate determination
with on-line supercritical fluid extraction-high performance liquid chromatography via solid phase extraction,
Fresenius J. Anal. Chem. 358 (1997) 471.
w43x X. Yin, W. Frech, E. Hoffmann, C. Ludke,
¨
J. Skole,
Mercury speciation by coupling cold vapour atomic
absorption spectrometry with flow injection on-line
preconcentration and liquid chromatographic separation,
Fresenius J. Anal. Chem. 361 (1998) 761.
w44x S. Olsen, L.C.R. Pessenda, J. Ruzicka, E.H. Hansen,
Combination of flow injection analysis with flame
atomic absorption spectrophotometry: determination of
trace amounts of heavy metals in polluted seawater,
Analyst 108 (1983) 905.
w45x Z. Fang, J. Ruzicka, E.H. Hansen, An efficient flowinjection system with on-line ion-exchange preconcentration for the determination of trace amounts of heavy
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w46x
w47x
w48x
w49x
w50x
w51x
w52x
w53x
w54x
w55x
w56x
w57x
w58x
metals by atomic absorption spectrometry, Anal. Chim.
Acta 164 (1984) 23.
Z. Fang, Z. Zhu, S. Zhang, S. Xu, L. Guo, L. Sun, Online separation and preconcentration in flow injection
analysis, Anal. Chim. Acta 214 (1988) 41.
Z. Fang, M. Sperling, B. Welz, Flow injection on-line
sorbent extraction preconcentration for graphite furnace
atomic absorption spectrometry, J. Anal. At. Spectrom.
5 (1990) 639.
A.N. Anthemidis, G.A. Zachariadis, J.A. Stratis, Online solid phase extraction system using PTFE packed
column for the flame atomic absorption spectrometric
determination of copper in water samples, Talanta 54
(2001) 935.
A.N. Anthemidis, G.A. Zachariadis, J.-S. Kougoulis,
J.A. Stratis, Flame atomic absorption spectrometric
determination of chromium(VI) by on-line preconcentration system using a PTFE packed column, Talanta 57
(2002) 15.
G.A. Zachariadis, A.N. Anthemidis, P.G. Bettas, J.A.
Stratis, Determination of lead by on-line solid phase
extraction using a PTFE micro-column and flame atomic
absorption spectrometry, Talanta 57 (2002) 919.
M. Zougagh, A. Garcia de Torres, J.M. Cano Pavon,
Determination of cadmium in water by ICP–AES with
on-line adsorption preconcentration using DPTH-gel and
TS-gel microcolumns, Talanta 56 (2002) 753.
D.A. Weeks, K.W. Bruland, Improved method for shipboard determination of iron in seawater by flow injection analysis, Anal. Chim. Acta 453 (2002) 21.
Q. Pu, Q. Sun, Z. Hu, S. Su, Application of 2mercaptobenzothiazole-modified silica gel to on-line
preconcentration and separation of silver for its atomic
absorption spectrometric determination, Analyst 123
(1998) 239.
S. Zhang, Q. Pu, P. Liu, Q. Sun, Z. Su, Synthesis of
amidinothioueido–silica gel and its application to flame
atomic absorption spectrometric determination of silver,
gold and palladium with on-line preconcentration and
separation, Anal. Chim. Acta 452 (2002) 223.
M. Fernandez Garcia, R. Pereiro Garcia, N.
Bordel Garcia, A. Sanz-Medel, On-line preconcentration
of inorganic mercury and methylmercury in sea-water
by sorbent-extraction and total mercury determination
by cold vapour atomic absorption spectrometry, Talanta
41 (1994) 1833.
Z.-S. Liu, S.-D. Huang, Automatic on-line preconcentration system for graphite furnace atomic absorption
spectrometry for the determination of trace metals in
sea water, Anal. Chim. Acta 281 (1993) 185.
A. Ali, X. Yin, H. Shen, Y. Ye, X. Gu, 1,10-Phenanthroline as a complexing agent for on-line sorbent
extractionypreconcentration for flow injection-flame
atomic absorption spectrometry, Anal. Chim. Acta 392
(1999) 283.
P.-G. Su, S.-D. Huang, Use of 4-(2-pyridylazo)resorcinol or 2-(2-pyridylazo)-5-dimethylamino-
w59x
w60x
w61x
w62x
w63x
w64x
w65x
w66x
w67x
w68x
w69x
w70x
1225
phenol as chelating agent for determination of cadmium
in seawater by atomic absorption spectrometry with online flow-injection sorbent extraction, Anal. Chim. Acta
376 (1998) 305.
T. Prasada Rao, S. Karthikeyan, B. Vijayalekshmy,
C.S.P. Iyer, Speciative determination of chromium(VI)
and chromium(III) using flow-injection on-line preconcentration and flame atomic-absorption spectrometric
detection, Anal. Chim. Acta 369 (1998) 69.
M. Sperling, X. Yin, B. Welz, Differential determination
of chromium(VI) and total chromium in natural waters
using flow injection on-line separation and preconcentration electrothermal atomic absorption spectrometry,
Analyst 117 (1992) 629.
Y. Ye, A. Ali, X. Yin, Cobalt determination with FIFAAS after on-line sorbent preconcentration using lnitroso-2-naphthol, Talanta 57 (2002) 945.
R. Lima, K.C. Leandro, R.E. Santelli, Lead preconcentration onto C18-minicolumn in continuous flow and its
determination in biological and vegetable samples by
flame atomic absorption spectrometry, Talanta 43
(1996) 977.
S.P. Quinaia, J.B.B. Da Silva, M.C.E. Rollemberg, A.J.
Curtius, Preconcentration of lead complexed with O,Odiethyl-dithiophosphate by column solid-phase extraction using different sorbents in a flow injection system
coupled to a flame atomic absorption spectrometer,
Talanta 54 (2001) 687.
A.C.P. Monteiro, L.S.N. Andrade, R.C. Campos, Online mercury and methylmercury pre-concentration by
adsorption of their dithiophosphoric acid diacylester
chelates on a C18 column and cold-vapor atomic-absorption detection, Fresenius J. Anal. Chem. 371 (2001)
353.
J. Ruzicka, A. Arndal, Sorbent extraction in flow injection analysis and its application to enhancement of
atomic spectrometry, Anal. Chim. Acta 216 (1989) 243.
Z.F. Queiroz, F.R.P. Rocha, G. Knapp, F.J. Krug, Flow
system with in-line separationypreconcentration coupled
to graphite furnace atomic absorption spectrometry with
W–Rh permanent modifier for copper determination in
seawater, Anal. Chim. Acta 463 (2002) 275.
L.S.G. Teixeira, F.R.P. Rocha, M. Korn, B.F. Reis, S.L.C.
Ferreira, A.C.S. Costa, Flow-injection solid-phase spectrophotometry for the determination of zinc in pharmaceutical preparations, Anal. Chim. Acta 383 (1999) 309.
´
S. Blain, P. Treguer,
Iron(II) and iron(III) determination
in sea water at the nanomolar level with selective online preconcentration and spectrophotometric determination, Anal. Chim. Acta 308 (1995) 425.
E. Vassileva, N. Furuta, Application of high-surfacearea ZrO2 in preconcentration and determination of 18
elements by on-line flow injection with inductively
coupled plasma atomic emission spectrometry, Fresenius
J. Anal. Chem. 370 (2001) 52.
A.G. Cox, I.G. Cook, C.W. McLeod, Rapid sequential
determination of chromium(III)–chromium(VI) by flow
1226
w71x
w72x
w73x
w74x
w75x
w76x
w77x
w78x
w79x
w80x
w81x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
injection analysis-inductively coupled plasma atomicemission spectrometry, Analyst 110 (1985) 331.
M. Sperling, S. Xu, B. Welz, Determination of chromium(III) and chromium(VI) in water using flow injection
on-line preconcentration with selective adsorption on
activated alumina and flame atomic absorption spectrometric detection, Anal. Chem. 64 (1992) 3101.
M.J. Marques, A. Morales-Rubio, A. Salvador, M.
de la Guardia, Chromium speciation using activated
alumina microcolumns and sequential injection analysisflame atomic absorption spectrometry, Talanta 53
(2001) 1229.
A.G. Cox, C.W. McLeod, Preconcentration and determination of trace chromium(III) by flow injectiony
inductively-coupled plasmayatomic emission spectrometry, Anal. Chim. Acta 179 (1986) 487.
S. Nielsen, E.H. Hansen, Selective flow-injection quantification of ultra-trace amounts of Cr(VI) via on-line
complexation and preconcentration with APDC followed by determination by electrothermal atomic
absorption spectrometry, Anal. Chim. Acta 366 (1998)
163.
W. Som-Aum, S. Liawruangrath, E.H. Hansen, Flow
injection on-line preconcentration of low levels of
Cr(VI) with detection by ETAAS. Comparison of using
an open tubular PTFE knotted reactor and a column
reactor packed with PTFE beads, Anal. Chim. Acta 463
(2002) 99.
C. Shuyu, Z. Zhifeng, Y. Huaming, Dithione as chelator
in the flow injection separation and pre-concentration
system of trace metals in biological samples, Anal.
Chim. Acta 451 (2002) 305.
Z. Fang, S. Xu, L. Dong, W. Li, Determination of
cadmium in biological materials by flame atomic
absorption spectrometry with flow-injection on-line
sorption preconcentration, Talanta 41 (1994) 2165.
R. Compano, R. Ferrer, J. Guiteras, M.D. Prat, Spectrofluorimetric detection of zinc and cadmium with 8(benzene sulfonamido)-quinoline immobilized on a
polymeric matrix, Analyst 119 (1994) 1225.
I.A. Kovalev, L.V. Bogacheva, G.I. Tsysin, A.A. Formanovsky, Y.A. Zolotov, FIA-FAAS system including
on-line solid phase extraction for the determination of
palladium, platinum and rhodium in alloys and ores,
Talanta 52 (2000) 39.
P. Hashemi, A. Olin, Equilibrium and kinetic properties
of a fast iminodiacetate based chelating ion exchanger
and its incorporation in a FIA-ICP–AES system, Talanta
44 (1997) 1037.
R.M. Cespon-Romero, M.C. Yebra-Biurrun, M.P. Bermejo-Barrera, Preconcentration and speciation of chromium by the determination of total chromium and
chromium(III) in natural waters by flame atomic
absorption spectrometry with a chelating ion-exchange
flow injection system, Anal. Chim. Acta 327 (1996)
37.
w82x N.G. Beck, R.P. Francks, K.W. Bruland, Analysis of Cd,
Cu, Ni, Zn and Mn in estuarine water by inductively
coupled plasma mass spectrometry coupled with an
automated flow injection system, Anal. Chim. Acta 455
(2002) 11.
w83x S. Matsuoka, Y. Tennichi, K. Takehara, K. Yoshimura,
Flow analysis of micro amounts of chromium(III) and
(VI) in natural water by solid phase spectrophotometry
using diphenylcarbazide, Analyst 124 (1999) 787.
w84x C.E.S. Miranda, B.F. Reis, N. Baccan, A.P. Packer, M.F.
´ Automated flow analysis system based on multiGine,
commutation for Cd, Ni and Pb on-line pre-concentration in a cationic exchange resin with determination by
inductively coupled plasma atomic emission spectrometry, Anal. Chim. Acta 453 (2002) 301.
w85x K. Yoshimura, S. Matsuoka, Y. Inokura, U. Hase, Flow
analysis for trace amounts of copper by ion-exchanger
phase absorptiometry with 4,7-diphenyl-2,9-dimethyl1,10-phenanthroline disulfonate and its application to
the study of karst groundwater storm runoff, Anal.
Chim. Acta 268 (1992) 225.
w86x J.A. Gomes Neto, A.P. Oliveira, G.P.G. Feshi, C.S.
Dakuzaku, M. Moraes, Minimization of lead and copper
interferences on spectrophotometric determination of
cadmium using electrolytic deposition and ion-exchange
in multi-commutation flow system, Talanta 53 (2000)
497.
w87x J.B.B. Silva, M.B.O. Giacomelli, A.J. Curtius, Determination of bismuth in aluminium and in steels by
electrothermal atomic absorption spectrometry after online separation using a minicolumn of activated carbon,
Analyst 124 (1999) 1249.
w88x R.E. Santelli, M. Gallego, M. Valcarcel, Preconcentration and atomic absorption determination of copper
traces in waters by on-line adsorption-elution on an
activated carbon microcolumn, Talanta 41 (1994) 817.
w89x H. Zhang, X. Yuan, X. Zhao, Q. Jin, On-line preconcentration with activated carbon for microwave plasma
torch atomic emission spectrometry, Talanta 44 (1997)
1615.
w90x S. Lin, C. Zheng, G. Yun, Determination of palladium
by flame atomic absorption spectrometry combined online with flow injection preconcentration using a microcolumn packed with activated carbon fibre, Talanta 42
(1995) 921.
w91x S.K. Xu, M. Sperling, B. Welz, Flame atomic absorption
spectrometric determination of cadmium and copper in
biological reference materials using on-line sorbent
extraction preconcentration, Fresenius J. Anal. Chem.
344 (1992) 535.
w92x C.S.L. Ferreira, D.S. Jesus, R.J. Cassella, A.C.S. Costa,
M.S. Carvalho, R.E. Santelli, An on-line solid phase
extraction system using polyurethane foam for the
spectrophotometric determination of nickel in silicates
and alloys, Anal. Chim. Acta 378 (1999) 287.
w93x S. Tsakovski, K. Benkhedda, E. Ivanova, F.C. Adams,
Comparative study of 8-hydroxyquinoline derivatives as
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w94x
w95x
w96x
w97x
w98x
w99x
w100x
w101x
w102x
w103x
w104x
w105x
w106x
w107x
chelating reagents for flow-injection preconcentration of
cobalt in a knotted reactor, Anal. Chim. Acta 453 (2002)
143.
S.D. Hartenstein, J. Ruzicka, G.D. Christian, Sensitivity
enhancement for flow injection analysis-inductively
coupled plasma atomic emission spectrometry using an
on-line preconcentration ion-exchange column, Anal.
Chem. 57 (1985) 21.
K. Benkhedda, H.G. Infante, F.C. Adams, E. Ivanova,
Inductively coupled plasma mass spectrometry for trace
analysis using flow injection on-line preconcentration
and time-of-flight mass analyser, Trends Anal. Chem.
21 (2002) 332.
J.N. King, J.S. Fritz, Concentration of metal ions by
complexation
with
sodium
bis(2-hydroxyethyl)dithiocarbamate and sorption on XAD-4 resin,
Anal. Chem. 57 (1985) 1016.
C. Kantipuly, S. Katragadda, A. Chow, H.D. Gesser,
Chelating polymers and related supports for separation
and preconcentration of trace metals, Talanta 37 (1990)
491.
C. Gueguen, J. Dominck, D. Perret, Use of chelating
resins and inductively coupled plasma mass spectrometry for simultaneous determination of trace and major
elements in small volumes of saline water samples,
Fresenius J. Anal. Chem. 370 (2001) 909.
O. Abollino, M. Aceto, M.C. Bruzzoniti, E. Mentasti,
C. Sarzanini, Speciation of copper and manganese in
milk by solid-phase extractionyinductively coupled plasma-atomic emission spectrometry, Anal. Chim. Acta
375 (1998) 299.
A. Tong, Y. Akama, S. Tanak, Pre-concentration of
copper, cobalt and nickel with 3-methyl-l-phenyl-4stearoyl-5-pyrazolone loaded on silica gel, Analyst 115
(1990) 947.
K. Terada, K. Matsumoto, Y. Taniguchi, Preconcentration of palladium(II) from water with thionalide loaded
onto silica gel, Anal. Chim. Acta 147 (1983) 411.
K. Terada, K. Matsumoto, T. Inaba, Differential preconcentration of arsenic(III) and arsenic(V) with thionalide
loaded on silica gel, Anal. Chim. Acta 158 (1984) 207.
K. Terada, K. Nakamura, Preconcentration of cobalt(II)
in natural waters with 1-nitroso-2-naphthol supported
on silica gel, Talanta 28 (1981) 123.
M.E. Mahmoud, M.M. Osman, M.E. Amer, Selective
pre-concentration and solid phase extraction of mercury(II) from natural water by silica gel-loaded dithizone
phases, Anal. Chim. Acta 415 (2000) 33.
M.E. Mahmoud, G.A. Gohar, Silica gel-immobilizeddithioacetal derivatives as potential solid phase extractors for mercury(II), Talanta 51 (2000) 77.
M.E. Mahmoud, Selective solid phase extraction of
mercury(II) by silica gel-immobilized-dithiocarbamate
derivatives, Anal. Chim. Acta 398 (1999) 297.
Y. Sohrin, S.-I. Iwamoto, S. Akiyama, T. Fujita, T.
Kugii, H. Obata, E. Nakayama, S. Goda, Y. Fujishima,
H. Hasegawa, K. Ueda, M. Matsui, Determination of
w108x
w109x
w110x
w111x
w112x
w113x
w114x
w115x
w116x
w117x
w118x
w119x
w120x
1227
trace elements in seawater by fluorinated metal alkoxide
glass-immobilized 8-hydroxyquinoline concentration
and high-resolution inductively coupled plasma mass
spectrometry detection, Anal. Chim. Acta 363 (1998)
11.
E. Vassileva, K. Hadjiinov, T. Stoychev, C. Daiev,
Chromium speciation analysis by solid-phase extraction
on a high surface area TiO2, Analyst 125 (2000) 693.
E. Vassileva, I. Proinova, K. Hadjiivanov, Solid-phase
extraction of heavy metal ions on a high surface area
titanium dioxide, Analyst 121 (1996) 607.
A.C. Sahayam, Speciation of Cr(III) and Cr(VI) in
potable waters by using activated neutral alumina as
collector and ET-AAS for determination, Anal. Bioanal.
Chem. 372 (2002) 840.
K. Pyrzynska, P. Drzewicz, M. Trojanowicz, Preconcentration and separation of inorganic selenium species on
activated alumina, Anal. Chim. Acta 363 (1998) 141.
R. Compano, M. Granados, C. Leal, M.D. Prat, Solidphase extraction and spectrofluorimetric determination
of triphenyltin in environmental samples, Anal. Chim.
Acta 283 (1993) 272.
J. Saurina, C. Leal, R. Compano, M. Granados, R.
Tauler, M.D. Prat, Determination of triphenyltin in seawater by excitation–emission matrix fluorescence and
multivariate curve resolution, Anal. Chim. Acta 409
(2000) 237.
R.E. Sturgeon, S.N. Willie, S.S. Berman, Preconcentration of selenium and antimony from seawater for determination by graphite furnace atomic absorption
spectrometry, Anal. Chem. 57 (1985) 6.
R.E. Sturgeon, S.S. Berman, S.N. Willie, Concentration
of trace metals from sea-water by complexation with 8hydroxyquinoline and adsorption on C18-bonded silica
gel, Talanta 29 (1982) 167.
Y. Yamini, A. Tamaddon, Solid-phase extraction and
spectrophotometric determination of trace amounts of
copper in water samples, Talanta 49 (1999) 119.
Y. Yamini, N. Amiri, Solid-phase extraction, separation,
and visible spectrophotometric determination of trace
amounts of iron in water samples, J. AOAC Int. 84
(2001) 713.
¨
M.D. Muller,
Comprehensive trace level determination
of organotin compounds in environmental samples using
high-resolution gas chromatography with flame photometric detection, Anal. Chem. 59 (1987) 617.
M. Shamsipur, A. Avanes, M.K. Rofouei, H. Sharghi,
G. Aghapour, Solid-phase extraction and determination
of ultra trace amounts of copper(II) using octadecyl
silica membrane disks modified by 11-hydroxynaphthacene-5,12-quinone and flame atomic absorption spectrometry, Talanta 54 (2001) 863.
O.R. Hashemi, M.R. Kargar, F. Raoufi, A. Moghimi, H.
Aghabozorg, M.R. Ganjali, Separation and preconcentration of trace amounts of lead on octadecyl silica
membrane disks modified with a new S-containing
1228
w121x
w122x
w123x
w124x
w125x
w126x
w127x
w128x
w129x
w130x
w131x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
Schiff’s base and its determination by flame atomic
absorption spectrometry, Microchem. J. 69 (2001) 1.
M. Shamsipur, F. Raoufi, H. Sharghi, Solid phase
extraction and determination of lead in soil and water
samples using octadecyl silica membrane disks modified
by biswl-hydroxy-9,10-anthraquinone-2-methylxsulphide
and flame atomic absorption spectrometry, Talanta 52
(2000) 637.
D.W. King, J. Lin, D.R. Kester, Spectrophotometric
determination of iron(II) in seawater at nanomolar
concentrations, Anal. Chim. Acta 247 (1991) 125.
Z. Yi, G. Zhuang, P.R. Brown, R.A. Duce, Highperformance liquid chromatographic method for the
determination of ultratrace amounts of iron(II) in aerosols, rainwater, and seawater, Anal. Chem. 64 (1992)
2826.
Z.-S. Liu, S.-D. Huang, Determination of copper and
cadmium in sea water by preconcentration and electrothermal atomic absorption spectrometry, Anal. Chim.
Acta 267 (1992) 31.
M. Shamsipur, A.R. Ghiasvand, Y. Yamini, Solid-phase
extraction of ultratrace uranium(VI) in natural waters
using octadecyl silica membrane disks modified by trin-octylphosphine oxide and its spectrophotometric
determination with dibenzoylmethane, Anal. Chem. 71
(1999) 4892.
M.B. Shabani, T. Akagi, A. Masuda, Preconcentration
of trace rare-earth elements in seawater by complexation
with bis(2-ethylhexyl) hydrogen phosphate and 2-ethylhexyl dihydrogen phosphate adsorbed on a C18 cartridge
and determination by inductively coupled plasma mass
spectrometry, Anal. Chem. 64 (1992) 737.
Y. Yamini, M. Chaloosi, H. Ebrahimzadeh, Solid phase
extraction and graphite furnace atomic absorption spectrometric determination of ultra trace amounts of bismuth in water samples, Talanta 56 (2002) 797.
Y. Yamini, J. Hassan, R. Mohandesi, N. Bahramifar,
Preconcentration of trace amounts of beryllium in water
sample on octadecyl silica cartridges modified by quinalizarine and its determination with atomic absorption
spectrometry, Talanta 56 (2002) 375.
M. Shamsipur, M.H. Mashhadizadeh, Preconcentration
of trace amounts of silver ion in aqueous samples on
octadecyl silica membrane disks modified with hexathia-18-crown-6 and its determination by atomic absorption spectrometry, Fresenius J. Anal. Chem. 367 (2000)
246.
Y. Yamini, N. Alizadeh, M. Shamsipur, Solid phase
extraction and determination of ultra trace amounts of
mercury(II) using octadecyl silica membrane disks modified by hexathia-18-crown-6-tetraone and cold vapour
atomic absorption spectrometry, Anal. Chim. Acta 355
(1997) 69.
R.J. Kvitek, J.F. Evans, P.W. Carr, Diamineysilanemodified controlled pore glass. The covalent attachment
reaction from aqueous solution and the mechanism of
w132x
w133x
w134x
w135x
w136x
w137x
w138x
w139x
w140x
w141x
w142x
w143x
w144x
reaction of bound diamine with copper(II), Anal. Chim.
Acta 144 (1982) 93.
A.R. Sarkar, P.K. Datta, M. Sarkar, Sorption recovery
of metal ions using silica gel modified with salicylaldoxime, Talanta 43 (1996) 1857.
K. Terada, K. Matsumoto, H. Kimura, Sorption of
copper(II) by some complexing agents loaded on various supports, Anal. Chim. Acta 153 (1983) 237.
R.E. Sturgeon, S.S. Berman, S.N. Willie, J.A.H. Desaulniers, Preconcentration of trace elements from seawater
with silica-immobilized 8-hydroxyquinoline, Anal.
Chem. 53 (1981) 2337.
J.W. McLaren, A.P. Mykytiuk, S.N. Willie, S.S. Berman,
Determination of trace metals in seawater by inductively
coupled plasma mass spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline, Anal.
Chem. 57 (1985) 2907.
R. Kocjan, S. Przeszlakowski, Calcon-modified silica
gel sorbent. Application to preconcentration or elimination of trace metals, Talanta 39 (1992) 63.
D.E. Leyden, G.H. Luttrell, A.E. Sloan, N.J. DeAngelis,
Characterization and application of silylated substrates
for the preconcentration of cations, Anal. Chim. Acta
84 (1976) 97.
T. Seshadri, H.-J. Haupt, Silica-immobilized 2-w(2-(triethoxysilyl)ethyl)thioxaniline as a selective sorbent for
the separation and preconcentration of palladium, Anal.
Chem. 60 (1988) 47.
P. Jones, P.J. Hobbs, L. Ebdon, A dithizone post-column
detector for the high-performance liquid chromatographic determination of trace metals, Anal. Chim. Acta 149
(1983) 39.
M.E. Mahmoud, M.S.M. Al Saadi, Selective solid phase
extraction and preconcentration of iron(III) based on
silica gel-chemically immobilized purpurogallin, Anal.
Chim. Acta 450 (2001) 239.
K.S. Abou-El-Sherbini, I.M.M. Kenawy, M.A. Hamed,
R.M. Issa, R. Elmorsi, Separation and preconcentration
in a batch mode of Cd(II), Cr(III, VI), Cu(II), Mn(II,
VII) and Pb(II) by solid-phase extraction by using of
silica modified with N-propylsalicylaldimine, Talanta 58
(2002) 289.
P. Lessi, N.L. Dias Filho, J.C. Moreira, J.T.S. Campos,
Sorption and preconcentration of metal ions on silica
gel modified with 2,5-dimercapto-1,3,4-thiadiazole,
Anal. Chim. Acta 327 (1996) 183.
R. Garcia-Valls, A. Hrdlicka, J. Perutka, J. Havel, N.V.
Deorkard, L.L. Tavlarides, M. Munoz, M. Valiente,
Separation of rare earth elements by high performance
liquid chromatography using a covalent modified silica
gel column, Anal. Chim. Acta 439 (2001) 247.
S. Hutchinson, G.A. Kearney, E. Horne, B. Lynch, J.D.
Glennon, M.A. McKervey, S.J. Harris, Solid phase
extraction of metal ions using immobilized chelating
calixarene tetrahydroxamates, Anal. Chim. Acta 291
(1994) 269.
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w145x R.M. Izatt, R.L. Bruening, M.L. Bruening, B.J. Tarbet,
K.E. Krakowiak, J.S. Bradshaw, J.J. Christensen,
Removal and separation of metal ions from aqueous
solutions using a silica-gel-bonded macrocycle system,
Anal. Chem. 60 (1988) 1825.
w146x M.L. Bruening, D.M. Mitchell, J.S. Bradshaw, R.M.
Izatt, R.L. Bruening, Effect of organic solvent and anion
type on cation binding constants with silica gel bound
macrocycles and their use in designing selective concentrator columns, Anal. Chem. 63 (1991) 21.
w147x G. Philippeit, J. Angerer, Determination of palladium in
human urine by high-performance liquid chromatography and ultraviolet detection after ultraviolet photolysis
and selective solid-phase extraction, J. Chromatogr. B
760 (2001) 237.
w148x V. Cuculic, M. Mlakar, M. Branica, Synergetic adsorption of copper(II) mixed ligand complexes onto the
SEP-PAK C18 column, Anal. Chim. Acta 339 (1997)
181.
w149x M.H. Pournaghi-Azar, Dj. Djozan, H.A. Zadeh, Determination of trace bismuth by solid phase extraction and
anodic stripping voltammetry in non-aqueous media,
Anal. Chim. Acta 437 (2001) 217.
w150x S.J. Kumar, P. Ostapczuk, H. Emons, Chromium speciation in water by electrothermal AAS after simultaneous
adsorption of Cr(III) and Cr(VI) on activated alumina
mini column, At. Spectrosc. 20 (1999) 194.
w151x J.L. Manzoori, M.H. Sorouraddin, F. Shemirani, Chromium speciation by a surfactant-coated alumina microcolumn using electrothermal atomic absorption
spectrometry, Talanta 42 (1995) 1151.
w152x E. Vassileva, K. Hadjiinov, Determination of trace elements in AR grade alkali salts after preconcentration by
column solid-phase extraction on TiO2 (anatase), Fresenius J. Anal. Chem. 357 (1997) 881.
w153x P. Liang, Y. Qin, B. Hu, C. Li, T. Peng, Z. Jiang, Study
on the adsorption behavior of heavy metal ions on
nanometer-size titanium dioxide with ICP–AES, Fresenius J. Anal. Chem. 368 (2000) 638.
w154x C.W. Huck, G.K. Bonn, Recent developments in polymer-based sorbents for solid-phase extraction, J. Chromatogr. A 885 (2000) 51.
w155x N. Masque,
´ R.M. Marce,
´ F. Borrull, New polymeric and
other types of sorbents for solid-phase extraction of
polar organic micropollutants from environmental water,
Trends Anal. Chem. 17 (1998) 384.
w156x L. Elci, L.M. Soylak, A. Uzun, E. Buyukpatir,
¨ ¨
M.
Dogan, Determination of trace impurities in some nickel
compounds by flame atomic absorption spectrometry
after solid phase extraction using Amberlite XAD-16
resin, Fresenius J. Anal. Chem. 368 (2000) 358.
w157x O. Abollino, M. Aceto, M.C. Bruzzoniti, E. Mentasti,
C. Sarzanini, Determination of metals in highly saline
matrices by solid-phase extraction and slurry-sampling
inductively coupled plasma–atomic emission spectrometry, Anal. Chim. Acta 375 (1998) 293.
1229
w158x S. Saracoglu,
¸
¸ Column solid-phase extraction
L. Elci,
with Chromosorb-102 resin and determination of trace
elements in water and sediment samples by flame atomic
absorption spectrometry, Anal. Chim. Acta 452 (2002)
77.
w159x K. Isshiki, Y. Sohrin, H. Karatani, E. Nakayama, Preconcentration of chromium(III) and chromium(VI) in
sea water by complexation with quinolin-8-ol and
adsorption on macroporous resin, Anal. Chim. Acta 224
(1989) 55.
w160x O. Abollino, E. Mentasti, V. Porta, C. Sarzanini, Immobilized 8-oxine units on different solid sorbents for the
uptake of metal traces, Anal. Chem. 62 (1990) 21.
w161x A. Tunceli,
¨
¸
A.R. Turker,
Speciation of Cr(III) and
Cr(VI) in water after preconcentration of its 1,5-diphenylcarbazone complex on amberlite XAD-16 resin and
determination by FAAS, Talanta 57 (2002) 1199.
w162x A.G. Howard, M.H. Arbab-Zavar, The preconcentration
of mercury and methylmercury on dithizone-coated
polystyrene beads, Talanta 26 (1979) 895.
w163x P. Bermejo-Barrera, G. Gonzalez-Campos, M. FerronNovais, A. Bermejo-Barrera, Column preconcentration
of organotin with tropolone-immobilized and their determination by electrothermal atomization absorption spectrometry, Talanta 46 (1998) 1479.
w164x P. Bermejo-Barrera, R.M. Anllo-Sendin, M.J. CantelarBarbazan, A. Bermejo-Barrera, Selective preconcentration and determination of tributyltin in fresh water by
electrothermal atomic absorption spectrometry, Anal.
Bioanal. Chem. 372 (2002) 837.
w165x C.S.L. Ferreira, C.F. de Brito, A.F. Dantas, N.M.
Lopo de Araujo, A.C.S. Costa, Nickel determination in
saline matrices by ICP–AES after sorption on Amberlite
XAD-2 loaded with PAN, Talanta 48 (1999) 1173.
w166x K. Isshiki, F. Tsuji, T. Kuwamoto, E. Nakayama, Preconcentration of trace metals from seawater with 7dodecenyl-8-quinolinol impregnated macroporous resin,
Anal. Chem. 59 (1987) 2491.
w167x A. Ramesh, K.R. Mohan, K. Seshaiah, Preconcentration
of trace metals on Amberlite XAD-4 resin coated with
dithiocarbamates and determination by inductively coupled plasma–atomic emission spectrometry in saline
matrices, Talanta 57 (2002) 243.
w168x A.N. Masi, R.A. Olsina, Preparation and characterization of chelating resins loaded with 2-(5-bromo-2pyridylazo)-5-(diethylamino)phenol for preconcentration of rare earth elements, Fresenius J. Anal. Chem.
357 (1997) 65.
w169x M.E. Leon-Gonzalez, L.V. Perez-Arribas, Chemically
modified polymeric sorbents for sample preconcentration, J. Chromatogr. A 902 (2000) 3.
w170x R. Saxena, A.K. Singh, S.S. Sambi, Synthesis of a
chelating polymer matrix by immobilizing Alizarin RedS on Amberlite XAD-2 and its application to the
preconcentration of lead(II), cadmium(II), zinc(II) and
nickel(II), Anal. Chim. Acta 295 (1994) 199.
1230
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w171x R. Saxena, A.K. Singh, D.P.S. Rathore, Salicylic acid
functionalized polystyrene sorbent Amberlite XAD-2.
Synthesis and applications as a preconcentrator in the
determination of zinc(II) and lead(II) by using atomic
absorption spectrometry, Analyst 120 (1995) 403.
w172x P.K. Tewari, A.K. Singh, Thiosalicylic acid-immobilized
Amberlite XAD-2: metal sorption behavior and applications in estimation of metal ions by flame atomic
absorption spectrometry, Analyst 125 (2000) 2350.
w173x R. Saxena, A.K. Singh, Pyrocatechol violet immobilized
Amberlite XAD-2: synthesis and metal-ion uptake properties suitable for analytical applications, Anal. Chim.
Acta 340 (1997) 285.
w174x P.K. Tewari, A.K. Singh, Amberlite XAD-2 functionalized with chromotropic acid: synthesis of a new polymer
matrix and its applications in metal ion enrichment for
their determination by flame atomic absorption spectrometry, Analyst 124 (1999) 1847.
w175x P.K. Tewari, A.K. Singh, Synthesis, characterization and
applications of pyrocatechol modified amberlite XAD2 resin for preconcentration and determination of metal
ions in water samples by flame atomic absorption
spectrometry, Talanta 53 (2001) 823.
w176x P.K. Tewari, A.K. Singh, Preconcentration of lead with
Amberlite XAD-2 and Amberlite XAD-7 based chelating resins for its determination by flame atomic absorption spectrometry, Talanta 56 (2002) 735.
w177x M. Kumar, D.P.S. Rathore, A.K. Singh, Metal ion
enrichment with Amberlite XAD-2 functionalized with
Tiron: analytical applications, Analyst 125 (2000) 1221.
w178x K. Dev, G.N. Rao, Preparation and analytical properties
of a chelating resin containing bicine groups, Talanta
42 (1995) 591.
w179x M.C. Yebra-Biurrun, M.C. Garcia-Dopazo, A. BermejoBarrera, M.P. Bermejo-Barrera, Preconcentration of trace
amounts of manganese from natural waters by means
of a macroreticular poly(dithiocarbamate)resin, Talanta
39 (1992) 671.
w180x N. Uehara, A. Katamine, Y. Shijo, High-performance
liquid chromatographic determination of cobalt(II) as
the
2-(5-bromo-2-pyridylazo)-5-diethylaminophenol
chelate after preconcentration with a cation-exchange
resin, Analyst 119 (1994) 1333.
w181x B.C. Mondal, D. Das, A.K. Das, Synthesis and characterization of a new resin functionalized with 2-naphthol3,6-disulfonic acid and its application for the speciation
of chromium in natural water, Talanta 56 (2002) 145.
w182x Y. Cai, G. Jiang, J. Liu, Preconcentration of cobalt with
8-hydroxyquinoline and gas chromatographic stationary
phase Chromosorb 105 and its determination by graphite
furnace atomic absorption spectrometry, Talanta 57
(2002) 1173.
w183x F. Shemirani, M. Rajabi, Preconcentration of chromium(III) and speciation of chromium by electrothermal
atomic absorption spectrometry using cellulose adsorbent, Fresenius J. Anal. Chem. 371 (2001) 1037.
w184x B. Sengupta, J. Das, Preconcentration of trace amounts
of mercury(II) in water on picolinic acid amide-containing resin, Anal. Chim. Acta 219 (1989) 339.
w185x P.K. Tewari, A.K. Singh, Amberlite XAD-7 impregnated
with Xylenol Orange; a chelating collector for preconcentration of Cd(II), Co(II), Cu(II), Ni(II), Zn(II) and
Fe(III) ions prior to their determination by flame AAS,
Fresenius J. Anal. Chem. 367 (2000) 562.
w186x B. Wen, X.-Q. Shuan, J. Lian, Separation of Cr(III) and
Cr(VI) in river and reservoir water with 8-hydroxyquinoline immobilized polyacrylonitrile fiber for determination by inductively coupled plasma mass
spectrometry, Talanta 56 (2002) 681.
w187x B. Gong, Y. Wang, ICP–AES determination of traces
of noble metal ions pre-concentrated and separated on
a new polyacrylacylaminothiourea chelating fiber, Anal.
Bioanal. Chem. 372 (2002) 597.
w188x B. Wen, X.-Q. Shuan, R.-X. Liu, H.-X. Tang, Preconcentration of trace elements in sea water with
poly(acrylaminophosphonic-dithiocarbamate) chelating
fiber for their determination by inductively coupled
plasma mass spectrometry, Fresenius J. Anal. Chem.
363 (1999) 251.
w189x K. Minagawa, Y. Takizawa, I. Kifune, Determination of
very low levels of inorganic and organic mercury in
natural waters by cold-vapor atomic absorption spectrometry after preconcentration on a chelating resin,
Anal. Chim. Acta 115 (1980) 103.
w190x S. Blain, P. Appriou, H. Handel, Preconcentration of
trace metals from sea water with the chelating resin
Chelamine, Anal. Chim. Acta 272 (1993) 91.
w191x S.-C. Pai, P.-Y. Whung, R.-L. Lai, Pre-concentration
effiency of Chelex-100 resin for heavy metals in seawater, Anal. Chim. Acta 211 (1988) 257.
w192x M.E. Malla, M.B. Alvarez, D.A. Batistoni, Evaluation
of sorption and desorption characteristics of cadmium,
lead and zinc on Amberlite IRC-718 iminodiacetate
chelating ion exchanger, Talanta 57 (2002) 277.
w193x M. Bueno, M. Potin-Gautier, Solid-phase extraction for
the simultaneous preconcentration of organic (selenocystine) and inorganic wSe(IV), Se(VI)x selenium in
natural waters, J. Chromatogr. A 963 (2002) 185.
w194x M. Llobat-Estelles, A.R. Mauri-Aucejo, M.D. LopezCatalan, Spectrophotometric determination of chromium
with diphenylcarbazide in the presence of vanadium,
molybdenum, and iron after separation by solid-phase
extraction, Fresenius J. Anal. Chem. 371 (2001) 358.
w195x A. Afkhami, T. Madrakian, A.A. Assl,
{ A.A. Sehhat,
Solid phase extraction flame atomic absorption spectrometric determination of ultra-trace beryllium, Anal.
Chim. Acta 437 (2001) 17.
w196x S. Hoshi, H. Fujisawa, K. Nakamura, S. Nakata, M.
Uto, K. Akatsuka, Preparation of Amberlite XAD resins
coated with dithiosemicarbazone compounds and preconcentration of some metal ions, Talanta 41 (1994)
503.
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
w197x B. Salih, R. Say, A. Denizli, O. Gene, E. Piskin,
Determination of inorganic and organic mercury compounds by capillary gas chromatography coupled with
atomic absorption spectrometry after preconcentration
on dithizone-anchored poly(ethylene glycol dimethacrylate-hydroxyehtylmethacrylate) microbeads, Anal.
Chim. Acta 371 (1998) 177.
w198x D.W. Lee, M. Halmann, Selective separation of nickel(II) by dimehtylglyoxime-treated polyurethane foam,
Anal. Chem. 48 (1976) 2214.
w199x T. Braun, A.B. Farag, Plasticized open-cell polyurethane
foam as a universal matrix for organic reagents in trace
element preconcentration. Part III. Collection of cobalt
traces on 1-nitroso-2-naphthol and diethyldithiocarbamate foams, Anal. Chim. Acta 76 (1975) 107.
w200x A. Alexandrova, S. Arpadjan, Determination of trace
elements in analytical-reagent grade sodium salts by
atomic absorption spectrometry and inductively coupled
plasma atomic emission spectrometry after preconcentration by column solid phase extraction, Analyst 118
(1993) 1309.
w201x D.S. Jesus, R.J. Cassella, S.L.C. Ferreira, A.C.S. Costa,
M.S. Carvalho, R.E. Santelli, Polyurethane foam as a
sorbent for continuous flow analysis: preconcentration
and spectrophotometric determination of zinc in biological materials, Anal. Chim. Acta 366 (1998) 263.
w202x C.S.L. Ferreira, H.C. Santos, D.S. Jesus, Molybdenum
determination in iron matrices by ICP–AES after separation and preconcentration using polyurethane foam,
Fresenius J. Anal. Chem. 369 (2001) 187.
w203x I.A. Veselova, T.N. Shekhovtsova, Visual determination
of lead(II) by inhibition of alkaline phosphatase immobilized on polyurethane foam, Anal. Chim. Acta 413
(2000) 95.
w204x S. Tian, G. Schwedt, Solid-phase extraction of the
chromium(III)-diphenylcarbazone complex prior to ionpair chromatography and application to geological samples, Fresenius J. Anal. Chem. 354 (1996) 447.
w205x I.E. De Vito, R.A. Olsina, A.N. Masi, Enrichment
method for trace amounts of rare earth elements using
chemofiltration and XRF determination, Fresenius J.
Anal. Chem. 368 (2000) 392.
w206x J.P. Riley, D. Taylor, Chelating resins for the concentration of trace elements from sea water and thier analytical
use in conjunction with atomic absorption spectrophotometry, Anal. Chim. Acta 40 (1968) 479.
w207x R. Boniforti, R. Ferraroli, P. Frigieri, D. Heltai, G.
Queirazza, Intercomparison of five methods for the
determination of trace metals in sea water, Anal. Chim.
Acta 162 (1984) 33.
w208x M. Pesavento, R. Biesuz, Sorption of divalent metal
ions on an iminodiacetic resin from artificial seawater,
Anal. Chim. Acta 346 (1997) 381.
w209x S.-C. Pai, Pre-concentration efficiency of Chelex-100
resin for heavy metals in seawater. Part 2. Distribution
of heavy metals on a Chelex-100 column and optimi-
w210x
w211x
w212x
w213x
w214x
w215x
w216x
w217x
w218x
w219x
w220x
w221x
w222x
1231
zation of the column efficiency by a plate simulation
method, Anal. Chim. Acta 211 (1988) 271.
C. Gueguen, C. Belin, B.A. Thomas, F. Monna, P.-Y.
Favarger, J. Dominik, The effect of freshwater UVirradiation prior to resin preconcentration of trace metals, Anal. Chim. Acta 386 (1999) 155.
H. Kumagai, T. Yokoyama, T.M. Suzuki, T. Suzuki,
Liquid chromatographic selectivity and retention behavior of rare-earth elements on a chelating resin having a
propylenediaminetetraacetate type functional group,
Analyst 124 (1999) 1595.
B. Wen, X.-Q. Shuan, S.-G. Xu, Preconcentration of
ultratrace rare earth elements in seawater with 8-hydroxyquinoline immobilized polyacrylonitrile hollow fiber
membrane for determination by inductively coupled
plasma mass spectrometry, Analyst 124 (1999) 621.
M.R. Buchmeiser, R. Tessadri, G. Seeber, G.K. Bonn,
Selective extraction of rare-earth elements from rocks
using a high-capacity cis-1,4-butanedioic acid-functionalized resin, Anal. Chem. 70 (1998) 2130.
F. Sinner, M.R. Buchmeiser, R. Tessadri, M. Mupa, K.
Wurst, G.K. Bonn, Dipyridyl amide-functionalized polymers prepared by ring-opening-metathesis polymerization (ROMP) for the selective extraction of mercury
and palladium, J. Am. Chem. Soc. 120 (1998) 2790.
D.J. Hutchinson, A.A. Schilt, Investigation of the
adsorption of ferroin-type ligands and metal chelates on
activated carbons for applications in reagent purification
and trace metal enrichment and determination, Anal.
Chim. Acta 154 (1983) 159.
A. Afkhami, T. Madrakian, Kinetic-spectrophotometric
determination of selenium in natural water after preconcentration of elemental selenium on activated carbon,
Talanta 58 (2002) 311.
E. Piperaki, H. Berndt, E. Jackwerth, Investigations on
the sorption of metal chelates on activated carbon, Anal.
Chim. Acta 100 (1978) 589.
Y. Petit de Pena, M. Gallego, M. Varcarcel, Flame
atomic absorption spectrometric determination of cadmium in biological samples using a preconcentration
flow system with an activated carbon column and
dithizone as a chelating agent, J. Anal. At. Spectrom. 9
(1994) 691.
T. Aydemir, S. Gucer, Determination of nickel in urine
by flame atomic absorption spectrometry after activated
carbon enrichment, Anal. Lett. 29 (1996) 351.
M. Soylak, I. Narin, L. Elci, M. Dogan, Atomic absorption-spectrometric determination of copper, cadmium,
lead and nickel in urine samples after enrichment and
separation procedure on an activated carbon column,
Trace Elem. Electrolytes 16 (1999) 131.
¨
M. Yaman, S. Gucer,
Determination of cadmium and
lead in vegetables after activated-carbon enrichment by
atomic absorption spectrometry, Analyst 120 (1995)
101.
T. Kubota, K. Suzuki, T. Okutani, Determination of
total selenium content in sediments and natural water
1232
w223x
w224x
w225x
w226x
w227x
w228x
w229x
w230x
w231x
w232x
w233x
w234x
w235x
w236x
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
by graphite furnace-atomic absorption spectroscopy
after collection as a selenium(IV) complex on activated
carbon, Talanta 42 (1995) 949.
T. Ferri, E. Cardarelli, B.M. Petronio, Determination of
tin and triorganotin compounds in sea-water by graphitefurnace atomic-absorption spectrophotometry, Talanta
36 (1989) 513.
M. Soylak, U. Divrikli, L. Elci, M. Dogan, Preconcentration of Cr(III), Co(II), Cu(II), Fe(III) and Pb(II) as
calmagite chelates on cellulose nitrate membrane filter
prior to their flame atomic absorption spectrometric
determinations, Talanta 56 (2002) 565.
K. Pyrzynska, Separation of inorganic selenium species
on anion-exchange resins, Analyst 120 (1995) 1933.
A. Bhalotra, B.K. Puri, Preconcentration of bismuth(III)
and copper(II) by solid-phase extraction and subsequent
determination by differential pulse polarography, J.
AOAC Intern. 84 (2001) 47.
B.K. Puri, M. Satake, G. Kano, S. Usami, Selective
preconcentration of iron in beverages and water samples
using 2,4,6-tri-2-pyridinyl-1,3,5-triazine-tetraphenylborate-naphthalene adsorbent, Anal. Chem. 59 (1987)
1850.
B.K. Puri, S. Balani, Preconcentration of iron(III),
cobalt(II) and copper(II) nitroso-R-complexes on
tetradecyldimehtylbenzylammonium iodie-naphthalene
adsorbent, Talanta 42 (1995) 337.
C.F. Poole, A.D. Gunatilleka, R. Sethuraman, Contributions of theory to method development in solid-phase
extraction, J. Chromatogr. A 885 (2000) 17.
M. Pesavento, E. Baldini, Study of sorption of copper(II) on complexing resin columns by solid phase
extraction, Anal. Chim. Acta 389 (1999) 59.
K. Hirose, Y. Dokiya, Y. Sugimura, Determination of
conditional stability constants of organic copper and
zinc complexes dissolved in seawater using ligand
exchange method with EDTA, Mar. Chem. 11 (1982)
343.
P.J.M. Buckley, C.M.G. van den Berg, Copper complexation profiles in the Atlantic ocean. A comparative
study using electrochemical and ion exchange techniques, Mar. Chem. 19 (1986) 281.
R. Ma, W. Van Mol, F. Adams, Determination of
cadmium, copper and lead in environmental samples.
An evaluation of flow injection on-line sorbent extraction for flame atomic absorption spectrometry, Anal.
Chim. Acta 285 (1994) 33.
W. Frenzel, Highly sensitive semi-quantitative field test
for the determination of chromium(VI) in aqueous
samples, Fresenius J. Anal. Chem. 361 (1998) 774.
S. Ahmad, R.C. Murthy, S.V. Chandra, Chromium speciation by column chromatography using a direct plasma
atomic emission spectrometer, Analyst 115 (1990) 287.
I. Kubrakova, T. Kudinova, A. Formanovsky, N. Kuz’min, G. Tsysin, Y. Zolotov, Determination of chromium(III) and chromium(VI) in river water by
electrothermal atomic absorption spectrometry after
w237x
w238x
w239x
w240x
w241x
w242x
w243x
w244x
w245x
w246x
w247x
w248x
w249x
sorption preconcentration in a microwave field, Analyst
119 (1994) 2477.
D.M. Adria-Cerezo, M. Llobat-Estelles, A.R. MauriAucejo, Preconcentration and speciation of chromium
in waters using solid-phase extraction and atomic
absorption spectrometry, Talanta 51 (2000) 531.
M.M. Gibbs, A simple method for the rapid determination of iron in natural waters, Water Res. 13 (1979)
295.
Y. Zhang, P. Riby, A.G. Cox, C.W. McLeod, A.R. Date,
Y.Y. Cheung, On-line pre-concentration and determination of lead in potable water by flow injection atomic
absorption spectrometry, Analyst 113 (1988) 125.
V.A. Lemos, S.L.C. Ferreira, On-line preconcentration
system for lead determination in seafood samples by
flame atomic absorption spectrometry using polyurethane foam loaded with 2-(2-benzothiazolylazo)-2-pcresol, Anal. Chim. Acta 441 (2001) 281.
P. Sooksamiti, H. Geckeis, K. Grudpan, Determination
of lead in soil samples by in-valve solid-phase extraction-flow injection flame atomic absorption spectrometry, Analyst 121 (1996) 1413.
C.-Y. Liu, Histidine as the functional group for a
chelating ion exchanger, Anal. Chim. Acta 192 (1987)
85.
E. Yamagami, S. Tateishi, A. Hashimoto, Application
of a chelating resin to the determination of trace
amounts of mercury in natural waters, Analyst 105
(1980) 491.
H. Emteborg, D.C. Baxter, W. Frech, Speciation of
mercury in natural waters by capillary gas chromatography with a microwave-induced plasma emission detector following preconcentration using a dithiocarbamate
resin microcolumn installed in a closed flow injection
system, Analyst 118 (1993) 1007.
T. Ferri, P. Sangiorgio, Determination of selenium speciation in river waters by adsorption on iron(III)Chelex-100 resin and differential pulse cathodic
stripping voltammetry, Anal. Chim. Acta 321 (1996)
185.
¨
U. Ornemark,
A. Olin, Preconcentration and separation
of inorganic selenium on Dowex IX8 prior to hydride
generation-atomic absorption spectrometry, Talanta 41
(1994) 67.
T. Kubota, T. Okutani, Determination of selenium content in natural water by grphite furnace atomic absorption spectrometry after preconcentration with
molybdate-form anion exchange resin, Anal. Chim. Acta
351 (1997) 319.
D. Tanzer, K.G. Heumann, Determination of dissolved
selenium species in environmental water samples using
isotope dilution mass spectrometry, Anal. Chem. 63
(1991) 1984.
W.M.R. Dirkx, R. Lobinski, F.C. Adams, Speciation
analysis of organotin in water and sediments by gas
chromatography with optical spectrometric detection
V. Camel / Spectrochimica Acta Part B 58 (2003) 1177–1233
after extraction separation, Anal. Chim. Acta 286 (1994)
309.
w250x J.L. Gomez-Ariza, E. Morales, I. Giraldez, D. SanchezRodas, A. Velasco, Sample treatment in chromatography-based speciation of organometallic pollutants, J.
Chromatogr. A 938 (2001) 211.
w251x J. Szpunar-Lobinska, M. Ceulemans, R. Lobisnki, F.C.
Adams, Flow-injection sample preparation for organotin
1233
speciation analysis of water by capillary gas chromatography-microwave-induced plasma atomic emission spectrometry, Anal. Chim. Acta 278 (1993) 99.
w252x Y. Cai, J.M. Bayona, Simultaneous speciation of
butyl-, phenyl-, and cyclohexyltin compounds in aqueous matrices using ethylation followed by solid-phase
trace enrichment, SFE, and GC determination, J. Chromatogr. Sci. 33 (1995) 89.