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Atomic absorption spectroscopy
(AAS)
‫اسپکتروسکوپی اتمی‬
‫•‬
‫جذب اتمی‬
‫•‬
‫نشر اتمی‬
‫•‬
‫فلورسانس اتمی‬
‫مراحل و فرآيند تشكيل اتم‬
‫‪ ‬انتقال محلول (بوسيله لوله موئينه)‬
‫‪ ‬تزريق و پاشيدن محلول و تبديل آن به ذرات ريز‬
‫‪ ‬انتقال ذرات ريز‬
‫‪ ‬تبخير و حذف حالل‬
‫‪ ‬تعادل بين ذرات تبخير شده‬
‫‪ ‬اندازه گيري نشر يا جذب‬
‫انواع اتمایزر‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫شعله‬
‫کوره گرافیتی‬
‫پالسما‬
‫قوس الکتریکی‬
‫جرقه الکتریکی‬
‫‪Atomizers‬‬
‫شعله ‪Flame‬‬
‫‪ ‬شعله واکنش ی است سریع و گرمازا که بين سوخت و اکسیدان‬
‫اتفاق می افتد‪.‬‬
‫اکسیدان‬
‫سوخت‬
‫ماکزيمم درجه حرارت )‪(C‬‬
‫هوا‬
‫استيلن‬
‫‪2250‬‬
‫اکسيد نيترو‬
‫استيلن‬
‫‪2955‬‬
‫هوا‬
‫پروپان‬
‫‪1725‬‬
‫هوا‬
‫هيدروژن‬
‫‪2045‬‬
‫انواع مشعل ها‬
‫‪‬‬
‫مشعل تمام مصرف کن‬
‫‪‬‬
‫مشعل پیش مخلوط‬
‫مشعل پیش مخلوط‬
Flame atomic absorption spectroscopy
Atomize
Ash
Dry
T I M E
Clean
Out
Cool
Down
T
E
M
P
Graphite furnace tube
Chemical modifier
Chemical Modifiers for Specific Elements in GFAAS
Analyte
Modifier
Effect
As
Ni
Pd
Permits a higher ashing temperature
and enhances the signal
Cd
H3PO4+
Mg(NO3)2
NH4H2PO4
Pd
Conversion to less volatile phosphate
which atomizes at a higher temperature
Pb
H3PO4+
Mg(NO3)2
NH4H2PO4
EDTA
citrate
oxalate
Permits a higher ashing temperature
and stabilizes the signal
AAS SET-UP
Hollow cathode Lamp (HCL)
A hollow cathode lamp for
Aluminum (Al)
Electrode less discharge lamp
(EDL)
Modulation
Interferences
1) Spectral interference
2) Chemical interference
‫تصحیح زمینه‬
‫‪Background Correction‬‬
‫‪ ‬مدوله کردن سیگنال برای حذف طیف های زمینه توسط‬
‫یک راه ساده است اما کافی نیست‪.‬‬
‫طاپر‬
‫‪ ‬راه ه ط ططای مفی ط ططد دیگ ط ططری وج ط ططود دارد از جمل ط ططه اس ط ططتفاده از م ط ط‬
‫دوتریم (‪.)D2‬‬
Zeeman effect
(ml=-1 )

(ml=0 )
+
(ml=+1 )
‫تکنیکهای افزایش حساسیت در‬
‫اسپکتروسکوپی اتمی‬
‫‪ ‬روش تولید بخار سرد ( ‪Cold vapor‬‬
‫‪)generation‬‬
‫‪ ‬روش تولید هیدریدهای فرار ( ‪Hydride‬‬
‫‪)generation‬‬
Cold vapor generation
Sn
2
 Hg
2
 Sn
4
 Hg ( L )
Hydride generation
As , Se
Metals
Analysis
Wet Digestion Methods

The common methods used for dissolving samples
for metals analysis are :
 Digestion in open flask
 Digestion in a pressurized sealed container
 Microwave assisted decomposition
Reagents Commonly used in Sample Dissolution or Digestion
Reagent
Sample Type
Water
Soluble salt
Dilute acids
Dry-ashed sample residues, easily oxidized
metals and alloys, salts
Concentrates acid (e.g., HNO3)
Less readily oxidized metals and alloys, steels,
metal oxides
Concentrates acid + oxidizing agent
Metals, alloys, soils, particulates from air,
refractory minerals, vegetable matter
Hydrofluoric acid
Silicates and other rock samples
Acid Digestion-Wet Ashing



The simplest method for wet digestion is carried out in an
open container.
Samples are dried, weighed, and placed in a beaker. The
digestion reagent is added.
The beaker is covered with a watch glass and placed on a
hot plate.
Aggressive acid digestion
Water
Dilute nitric acid
HNO3 + HCl
HNO3 + H2SO4
HNO3 + HClO4
HNO3 + HClO4 then HF
Aqua regia

For samples that show significant losses of analyte due to the
retention of metals in silica residues, the sample is first digested
thoroughly with HNO3 in a PTFE beaker. Then concentrated
HClO4 and a small amount of HF are added.

A mixture of an oxidizing acid with HF provides acidity,
oxidizing power, and complexation to dissolve all metals and
alloys and most refractory minerals, soils, rocks, and sediments.
Microwave Digestion

Advantages of digestion in a closed container :
• The containers are fabricated of high-temp polymers, which are less likely to
contain metal contaminants than are glass or ceramic beakers or crucibles.
• The sealed container eliminates the chance of airborne dust contamination.
• The sealed container reduce evaporation, so that less acid digestion solution is
required.
• The sealed container also eliminates losses of more volatile metal species, which
can be a problem in open container.
• The electronic controls on modern microwave digesters allow very reproducible
digestion conditions.
Dry Ashing

For samples that contain much organic matter, which are analyzed for
nonvolatile metals, dry ashing is a relatively simple method of
removing the organic matter.

A general procedure is to place the weighed sample into a platinum or
glass crucible and heat it in a furnace to a white ash. The temperature
should be kept at 400 to 450°C if any of the more volatile metals are
being determined. Salts or sulfuric acid may be added, if needed, and a
final ashing step can be done with HF if required. The residue is then
dissolved in concentrated nitric acid and water, and diluted to volume.
The final concentration of acid should be between 1 and 5%.
Extraction, Separation, and concentration

It is not always necessary or required to digest the entire
sample in order to free the metal for analysis. The
analyte of interest may be present as a soluble salt from a
pollution source or being present in the structure of the
mineral crystals.
Organic extraction of metals (LLE)
Extraction with Supercritical Fluids
Ultrasonic sample preparation
Solid-Phase Extraction for preconcentration
Structures of some chelating agents
Colorimetric Methods



Fairly rapid and simple analyses can be performed on solutions using a
variety of colorimetric reagents.
These are reagents that are more or less specific for certain metals and
will produce a solution, usually colored, whose absorbance at a
particular wavelength is related to the concentration of the analyte.
Preparation of samples for colorimetric analysis :
• Buffering or pH adjustment of sample solution
• Oxidize or reduce the analyte to bring it to the correct oxidation
state
• Add color-forming reagent
• Using specific condition of temp. or time to ensure complete
reaction
Some Colorimetric Reagents for Metals
Metal
Color Development Reagent
Wavelength
(nm)
Cr (VI)
1,5-Diphenylcarbazide
540
Pb
Dicyclohexyl-18-crown-6-dithizone
512
Fe (III)
Thiocyanate
460
Fe (II)
Pyrocatecol violet
570
Cd
Iodide and malachite green
685
Mn
Oxidize to permanganate with KIO4
525
Mg, Al
Precipitating with 8-hydroxyquinoline, dissolve in acid for
determination of hydroxyquinoline
590
Cu
Dithizone
510
Co, Ni, Cu, Zn
4-(2-Pyridylazo)resorcinol
510
Calibration Curves

The common calibration method is to prepare standards of known
concentrations, covering the concentration rang expected in the
sample.

The matrix standard should be as close to the samples as possible.
 If the sample is to be extracted into certain organic solvent, the
standards should be prepared in the same solvent.

The calibration curve is a plot of detector response as a function of
concentration
Typical calibration curve
The calibration can be done in two ways
•
1)
Measuring the amount of Pb in soil :
Sample preparation by acid extraction followed by analysis using
atomic absorption. The standards can be made by spiking clean soil
with known quantities of Pb. Then the standards are taken through
the entire process of extraction and analysis. Finally, the instrument
response is plotted as a function of concentration.
2)
The other option assumes quantitative extraction, and the standards
are used to calibrate only the AA.
The first approach is more accurate; the latter is simpler.
A calibration method that takes the matrix effects into account is the
method of standard addition.
Standard addition methods
Data for standard addition method
cx 
bcs
mVx