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ISCC 2014 Poster B.15 IMPROVED DEACTIVATION TECHNOLOGY FOR STAINLESS STEEL PROVIDES INERT SURFACE FOR GC ANALYSIS Laura Provoost 1 , John Oostdijk 1 , Peter Heijnsdijk 1 1 Agilent Technologies, Middelburg, The Netherlands Introduction 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 Conclusion Conclusion 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 UltiMetal Plus Figure 1. Rainbow appearance of UltiMetal Plus treated connectors and fittings (A) and inside of 1/8 inch tubing (B). 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. Appearance The most striking feature of parts treated with UltiMetal Plus is their rainbow appearance, from blue to silver metallic grey. 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 2. UltiMetal treatment on the outside of stainless steel tubing. 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. Metal on the outside of the column in the flow path Inlet UltiMate Union, inert Metal on the outside of the column in the flow path Flexible Metal ferrule 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). A B Inertness Comparison 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. Figure 4. Principle of a tandem- or post-column test. 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). # Compound ng* Category Interaction 1 Methane Alkane Unretained 2 Propionic acid 1 Acid Basicity 3 iso-Butyric acid 1 Acid Basicity 4 n-Butyric acid 1 Acid Basicity 5 Octene 0.5 Alkene polarity 6 Octane 0.5 Alkane (n-C8) Inert (hydrocarbon marker) 7 1-Nitrobutane 1 Alkane with NO 2 group Dipole interaction 8 4-Picoline 2 Base Acidity / silanol 9 Trimethyl Phosphate 5 Base Acidity / silanol (Retention Index shifting depending on amount silanol) 10 1,2-Pentanediol 2 di-alcohol Silanol / Metal impurity (A diol for the assessment of column damage (impact of oxygen/water – two very common contaminants), and silanol groups.) 11 Propylbenzene 1 Aromatic (inert) inert 12 1-Heptanol 1 Alcohol Silanol (inertaction with residual Si-H) 13 3-Octanone 1 Ketone Polarity 14 Decane 1 Alkane (n-C10) Inert (hydrocarbon marker) Table 1. Very Inert Mix test probes in dichloromethane (split 1:75), including surface interactions. * The calculated on-column amount after a split injection depended on the split ratio used. 12.5 12 11.5 11 10.5 10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 2.34 2.66 2.78 3.27 3.58 3.79 3.90 4.70 5.23 7.60 7.99 8.47 9.58 10.46 11.38 2.26 2.59 2.71 2.78 3.29 3.65 3.80 3.93 4.74 5.40 7.93 8.76 9.98 10.81 11.89 2.31 2.62 2.75 3.22 3.54 3.75 3.87 4.66 5.15 7.41 7.88 8.42 9.45 10.37 11.31 2.15 2.24 2.67 3.16 3.47 3.72 3.85 4.65 5.09 7.20 7.78 8.54 9.52 10.50 11.54 2.24 2.53 2.66 3.12 3.43 3.68 3.79 4.59 5.02 7.08 7.64 8.36 9.32 10.29 11.25 1.26 1.85 2.32 2.62 2.86 2.98 3.77 4.18 6.21 6.78 7.52 8.45 9.42 10.39 RT [min] pA XOffset : 0 YOffset : 23 A B C D E F 2 1 3 4 5 6 7 8 9 10 11 12 13 14 14 13 12 11 10 9 8 7 6 5 4 3 2 1 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. 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. 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). 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. Inlet (split mode) Detector (FID) Connector Reference column Tubing Figure 5. Tandem test of different 1 m x 1/8 inch tubing with a short test mix using a Megabore Agilent J&W VF- 5ms, 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. Literature Literature 1 Test mix 60 (0.01%) 1-octanol 2 n-undecane 3 2,6-dimethylphenol 4 2,6-dimethylaniline 5 n-dodecane 6 naphthalene 7 1-decanol 8 n-tridecane 9 decanoic acid ME 1 2 3 4 56 7 8 9 Bare SS UltiMetal SS UltiMetal Plus SS 1‐decanol Results 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.
