Download improved deactivation technology for stainless steel

IMPROVED DEACTIVATION TECHNOLOGY FOR
STAINLESS STEEL PROVIDES INERT SURFACE FOR
GC ANALYSIS
ISCC 2014
Poster B.15
Laura Provoost1, John Oostdijk1, Peter Heijnsdijk1
1Agilent Technologies, Middelburg, The Netherlands
Introduction
Modern GC and GC/MS instruments are important analytical tools for accurate and reproducible measurement of
many compounds at low ppb level in a wide variety of matrices. For accurate analyte measurement, compounds
need to survive the journey through the flow path. The flow path can contain different metal components, which
need to be deactivated when compounds are more (re)active than alkanes, for example pesticides, alcohols, or
very polar compounds.
Because analysts have to investigate reactive components at ever lower detection limits, UltiMetal deactivation
chemistry, which was developed in the 1980s, is now further improved and is known as UltiMetal Plus. The main
chemical process used to deposit the high-purity, high-performance chemically inert layer of UltiMetal Plus on
stainless steel surfaces is chemical vapor deposition (CVD). In a typical CVD process, the substrate is exposed to
one or more volatile precursors that react or decompose, or both, through thermal energy on its surface to produce
the desired deposit. The substrate does not react with the gases, but serves as a bottom layer. Depending on the
process parameters: precursor(s), pressure, temperature and time, the deposit layers differ in nature, density and
coverage. UltiMetal Plus technology is applied specifically to steel and stainless steel surfaces and can be used
safely when stainless steel products are defined or prescribed in a method.
UltiMetal Plus
Analytical advantages
Bare, untreated stainless steel has poor inertness characteristics, with metal oxides on the surface acting as
catalysts to many reactions that include dehydration of alcohols, cracking of hydrocarbons and esterification. The
UltiMetal Plus layer covers most of these metal oxides and, thus, reduces the reactivity of the steel surface, lowering
adsorption or catalytic breakdown of active compounds. The positive impact of the treatment at an analytical level is
most noticeable for trace concentrations, with less peak tailing and improved linearity of response for many sensitive
components.
UltiMetal Plus stainless steel capillary tubing has UltiMetal coating applied to the outside, as small areas of the
exterior are exposed to analyte interaction. Experiments demonstrated that the UltiMetal external coating improved
the inertness of the flow path.
Appearance
The most striking feature of parts treated with UltiMetal Plus is their rainbow appearance, from blue to silver metallic
grey.
Figure 2. UltiMetal treatment on the outside of stainless steel tubing.
Inlet
A
Metal on the outside of the
column in the flow path
B
UltiMate Union, Flexible Metal
ferrule
inert
Metal on the outside
of the column in the
flow path
Figure 1. Rainbow appearance of UltiMetal Plus treated connectors and fittings (A) and inside of 1/8 inch tubing (B).
The color variation results from the light diffraction qualities of the layers and differences in UltiMetal layer thickness,
which can vary between 700 and 1,000Å. The roughness of the underlying stainless steel surfaces will also impact
the final color appearance.
Figure 3. Examples of critical connections and active sites in a GC flow path.
A. installation in a GC inlet
B. Agilent Ultimate Union, inert (p/n G3182-60580) connecting a fused silica column to stainless steel UltiMetal
Plus tubing. There is a small area of the outside of the column that is in the flow path (correct length after
ferrule is 0.1 to 0.5 mm).
Inertness Comparison
Test method
A tandem-column setup was used to verify the inertness of the connector or tubing (Figure 4). The compounds were
first separated on a reference GC column, which was followed by a connector and a piece of tubing. The tubing was
connected to a flame ionization detector (FID). As system inertness is influenced by the total flow path, a system test
was performed to establish the base level inertness profile. To measure small differences in system activity a high
degree of initial inertness was required. The amount of analyte introduced in the column setup was calculated from
the injection volume, split ratio, and concentration of the test mixture.
The inertness of several steel deactivated tubing types, as well as deactivated fused silica, was compared (Figure
6). The system test, shown above (A), illustrates the initial inertness profile. Subsequent chromatograms show
inertness performance of different tubing types (5 m x 0.53 mm) with the same reference column and connector.
145
140
5 6
2.26
2.31
2.24
2.34
135
130
Detector (FID)
A
100
4
1
2
2.66
B
3.43 5
3
8
3.68
9.42
11
10
7.08
12
8.36
7.64
4.59
3.12
14
13
9.32
10.29
11.25
2.53
90
5.09
3.72
85
3.47
C
2.67
7.20
4.65
3.16
7.78
8.54
9.52
11.54
10.50
2.15
75
70
3.87
65
5.15
3.75
3.54
60
55
9
7
6
3.85
Connector
10.39
5.02
95
80
14
13
8.45
3.79
110
105
12
7.52
1.26
120
Tubing
6.78
3
115
Reference column
11
10
6.21
3.77
2.62
1
9
7
2.86
4
1.85
GC28B_UIUM-049_VIM2_9253640_CPM_Restek22501_1_1.DATA
GC28B_UIUM-049_VIM2_9253640_CPM_CP6540_1_1.DATA
GC28B_UIUM-049_VIM2_9253640_CPM_CP6581_1_1.DATA
GC28B_UIUM-049_VIM2_9253640_CPM_CP6577_1_1.DATA
GC28B_UIUM-049_VIM2_9253640_CPM_CP8009_1_1.DATA
GC28B_UIUM-049_VIM2_9253640_CPM_1_1.DATA
4.18
2.98
2.32
2
125
Inlet (split mode)
8
pA
XOffset : 0
YOffset : 23
D
2.75
4.66
7.88
3.22
8.42
9.45
11.31
10.37
7.41
2.62
50
Figure 4. Principle of a tandem- or post-column test.
3.80
40
To compare inertness of the connectors and tubing to untreated as well as differently treated products, the Very Inert
Mix is used. The probes in this test mix were chosen to be highly probative of the stationary phase and surface. The
active end of each compound is available to interact with any active sites on the product.
35
Compound
Methane
Propionic acid
iso-Butyric acid
n-Butyric acid
Octene
Octane
1-Nitrobutane
4-Picoline
Trimethyl Phosphate
1,2-Pentanediol
ng*
1
1
1
0.5
0.5
1
2
5
2
Category
Alkane
Acid
Acid
Acid
Alkene
Alkane (n-C8)
Alkane with NO2 group
Base
Base
di-alcohol
11
12
13
14
Propylbenzene
1-Heptanol
3-Octanone
Decane
1
1
1
1
Aromatic (inert)
Alcohol
Ketone
Alkane (n-C10)
10
8.76
5.40
9.98
10.81
11.89
7.93
2.59
3.90
3.79
5.23
3.58
2.78
F
8.47
4.70
3.27
7.99
2.66
9.58
11.38
10.46
7.60
5
RT [min]
0
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
Figure 6. Comparison of different types of tubing, 5 m x 0.53 mm, using the Very Inert Mix.
A. system check Agilent J&W VF-5ms (p/n CP8944) and Agilent Ultimate union (p/n G3182-60580)
B. non-polar (apolar) deactivated fused silica
C. UltiMetal Plus guard, stainless steel (p/n CP6577)
D. UltiMetal Plus tubing, stainless steel (p/n CP6581)
E. UltiMetal tubing, stainless steel (p/n CP6540)
F. non-Agilent inert deactivated tubing.
Tubing was tested using the tandem setup with the Very Inert Mix at 60 °C at constant hydrogen flow of 1.35
mL/min. On-column amounts and components are given in Table 1 (split 1:75, 1 µL injection).
Conclusion
Three different standard types of bulk tubing are available: 1/16 inch od (1 mm id), 1/8 inch od (2.1 mm id), and 1/4
inch od (4.3 mm id). The results in Figure 5 are for 1/8 inch tubing (1 m). Due to the large internal volume, a
Megabore VF-5ms GC column was used. Because there are no special deactivated connectors available to reduce
1/8 inch to 1/16 inch, standard metal connectors were UltiMetal Plus deactivated and used to connect a 1-m piece
of tubing. As a system reference set, a short piece (3 cm) of UltiMetal Plus deactivated 1/8 inch tubing was used
with two reducing unions, without cutting off the tubing (completely deactivated). Metal ferrules were used to
connect the fused silica tubing to the reducing union.
Bare SS
Compared to bare stainless steel, UltiMetal Plus-treated stainless steel provided greatly improved inertness.
Compared to non-Agilent tubing, an equal or better inertness was obtained. The deactivated exterior of UltiMetal
Plus tubing delivered the extra benefit of improved inertness when connecting the tubing to the instrument or
connectors. For inert, leak-tight and robust connections, the use of Agilent UltiMetal Plus connectors, ferrules, and
fittings is recommended.
Literature
1.
Anon. UltiMetal Plus – Advanced Chemistry for Stainless Steel Surface Deactivation. Technical Overview, Agilent
Technologies, Inc. Publication number 5991-3357EN (2014).
2. Anon. Agilent UltiMetal Plus Stainless Steel Deactivation for Tubing, Connectors, and Fittings. Technical Overview, Agilent
Technologies, Inc. Publication number 5991-4499EN (2014).
UltiMetal SS
UltiMetal Plus SS
2
5 6
3
4.74
3.29
15
Interaction
Unretained
Basicity
Basicity
Basicity
polarity
Inert (hydrocarbon marker)
Dipole interaction
Acidity / silanol
Acidity / silanol (Retention Index shifting depending on amount silanol)
Silanol / Metal impurity (A diol for the assessment of column damage (impact of
oxygen/water – two very common contaminants), and silanol groups.)
inert
Silanol (inertaction with residual Si-H)
Polarity
Inert (hydrocarbon marker)
1
2.71
20
Results
1
2
3
4
5
6
7
8
9
E
3.65
25
* The calculated on-column amount after a split injection depended on the split ratio used.
Test mix 60 (0.01%)
1-octanol
n-undecane
2,6-dimethylphenol
2,6-dimethylaniline
n-dodecane
naphthalene
1-decanol
n-tridecane
decanoic acid ME
2.78
30
Table 1. Very Inert Mix test probes in dichloromethane (split 1:75), including surface interactions.
#
1
2
3
4
5
6
7
8
9
10
3.93
45
4
1‐decanol
7
8
9
Figure 5. Tandem test of different 1 m x 1/8 inch tubing with a short test mix using a Megabore Agilent J&W VF5ms, 30 m x 0.53 mm, 0.5 µm GC reference column (p/n CP8974) (hydrogen constant flow at 4.7 mL/min, oven
120 °C). For this comparison QC test mix 60 is used.