Stationary phases silicone

Capillary gas chromatography is conducted with a cross-linked phenyl methyl silicone stationary phase (5%, 25 m x 0.2 mm x 0.5 pm film thickness, injector temp. 225°C, detector temp. 250°C, column temp. 40-200°C, 15°C/min after 1 min initial time). (Z)-2-Bromo-5-(trimethylsilyl)-2-penten-4-ynoic acid ethyl ester is observed to have a retention time of 14.0 min. GC data for bis(trimethylsilyl)butadiyne is as follows retention time 10.0 min, response factor (GC area produced relative to an equimolar quantity of (Z)-2-bromo-5-(trimethylsilyl)-2-penten-4-ynoic acid ethyl ester) 1.29. For (E)-2-[(trimethylsilyl)ethynyl]-5-(trimethylsilyl)-2-penten-4-ynoic acid ethyl ester the retention time is 17.0 min, the response factor 1.19. 

Conventional high pressure NICI spectra were obtained using a Hewlett-Packard 5985B quadrupole GC/MS, as described previously (1). Methane was used as the Cl reagent gas and was maintained in the source at 0.2-0.4 torr as measured through the direct inlet with a thermocouple gauge. A 200 eV electron beam was used to ionize the Cl gas, and the entire source was maintained at a temperature of 200° C. Samples were introduced into the spectrometer via the gas chromatograph which was equipped with a 25 meter fused silica capillary column directly interfaced with the ion source. For all experiments, a column coated with bonded 5% methyl phenyl silicon stationary phase, (Quadrex, Inc.) was used and helium was employed as the carrier gas at a head pressure of 20 lbs. Molecular sieve/silica gel traps were used to remove water and impurities from the carrier gas. 

Figure 6. Solvent analysis using a methyl silicone stationary phase.

Sulphonic acids and their salts are analysed by GC after esterification with diazomethane or after chlorination with thionyl chloride or phosgene [119]. Reaction with thionyl chloride proceeds according to Scheme 5.14. A 0.5-g sample of sulphonic acid or its salt is placed into a round-bottomed flask fitted with a magnetic stirrer and a reflux condenser, 0.5 ml of dimethylformamide and 20 ml of thionyl chloride are added and the mixture is refluxed for several minutes up to 2 h (according to the character of the sample) until the evolution of gas from the reaction mixture ceases (detection with the aid of a bubbler filled with chlorobenzene). If a salt is chlorinated, solid chloride produced in the reaction mixture must be removed by dilution with dichloromethane and by careful filtration through a fine glass filter. Excess of thionyl chloride and solvent is evaporated carefully under decreased pressure. The residue is dissolved in a suitable solvent (CCU) and analysed by GC (silicone stationary phase, temperature 160°C). 

Corina [147] reported retention data of benzyl esters of a number of acids from various biological materials on E-30 silicone stationary phase. 

TFA-methyl esters are very volatile. Their retention times on polyester stationary phases are up to six times shorter and on silicone stationary phases up to three times shorter than those of the corresponding acetyl methyl esters. A high volatility can also result in losses of the derivatives during their preparation, and therefore esterification with diazomethane is not recommended as mere evaporation of ethereal solution can cause significant losses of the derivatives of Ala, Val, Gly and Leu. If evaporation of the... 

Particular attention should be devoted to the selection of the column packing for the separation of TMS derivatives of amino acids as they are, as already mentioned, very sensitive towards moisture and can decompose on supports that have not been deactivated sufficiently. Silicone stationary phases of the SE-30, OV-1, OV-17 and DC-550 type and supports such as Gas-Chrom Q, Chromosorb W HP and Diatoport S have mostly been applied. One of the best GC separations of TMS derivatives of amino acids was obtained by Gehrke and Leimer [256] on a 6 m X 2 mm I.D. column packed with 10%... 

For the GC separation of TMS-phenylthiohydantoins different, mainly silicone, stationary phases have been utilized. A mixture of 7.33% of SP400, 5.33% of OV-210 and 0.66% of OV-225 at 190—210°C was recommended as the most suitable. SP-400 was also fairly suitable for the separation of phenylthiohydantoins of simple amino acids, including Tyr and Trp in a GC 55/65 system of a Beckman 890c sequence analyser. 

Trimethylsilyl derivatives are prepared by treatment with BSA alone [310,311] or with the addition of TMCS [312,314] in a suitable solvent (acetonitrile, pyridine, tetra-hydrofuran) or even without a solvent. For completion of the reaction, 10—20 min at 50°C are necessary [312], but as little as 30 min at 150°C has been reported for a stoppered vial with the use of a solvent [311], BSA alone can be used to advantage if pico-mole amounts are to be derivatized. The reaction products are said to decompose in dilute solutions even though pure BSA is used for dilution. At concentrations around 1 ng//d, up to 40% decomposition of the products is observed if diluted with BSA— acetonitrile (1 4), 100% decomposition occurs in 20 min. Of other silylating agents, e.g., HMDS and TMCS have been tested, but conversion into derivatives was not complete [311]. Silicone stationary phases of the SE-30, OV-1 and similar types have been used in the analysis. In most instances, temperature programming is required. Using the FID (in almost all instances), the detection limit is about 20 ng for T4 and 5—20 ng for T3, whereas with the aid of an ECD amounts about two orders of magnitude smaller can be detected [310,314]. Fig. 5.21 demonstrates a typical separation of five iodoamino acids and Tyr on 0.5% of SE-30. 

Another methylation method makes use of a reaction with iodomethane and a catalyst [478], as follows. About 30 mg of an oil dispersion of sodium hydride was washed three times with anhydrous diethyl ether, dried under a mild stream of nitrogen and suspended in 1 ml of freshly distilled dimethyl sulphoxide. A 200-jul portion of this suspension was added to ca. 1 /amol of phenylurea dissolved in 100 pi of pure dimethyl sulphoxide followed immediately by 50 pi of iodomethane. Reaction was allowed to proceed for 5—10 min with continuous stirring. Then 1 ml of water was carefully added and the mixture was extracted with three 1-ml portions of diethyl ether or light petroleum. The extracts were dried with anhydrous sodium sulphate, filtered and evaporated to dryness under a stream of nitrogen. Silicone stationary phases [OV-225 at 108°C or a mixture of DC-200 and QF-1 (1 3) at 170°C] were used. 

For the GC analysis of these substances trimethylsilyl derivatives are mostly prepared. Chloramphenicol is silylated with the aid of BSA [520,521 ]. Some workers [522], however, prefer an HMDS—TMCS mixture in pyridine as it is said to result in a more uniform product. The analysis is performed on silicone stationary phases of the SE-30 and OV-17 types. The related thiamphenicol is converted into the TMS derivative by treatment with BSA [523,524] and the same stationary phases are used for GC. If this method is applied to the determination of these substances in plasma and body fluids, and a selective detector is used (63Ni ECD), a sensitivity of determination of 0.1 jug/ml can be reached. 

Tsuji and Robertson analysed aminoglycoside antibiotics by GC of kanamycin, paromomycin and neomycin [525] and tetracyclines [526] after their silylation with a BSA-TMCS mixture in pyridine (1 1 2, v/v) or with commercially available Tri Sil Z reagent. The reaction was performed at room temperature for 24 h or at 75°C for 45 min. Good results with respect to peak symmetry and the separation of various compounds were obtained on silicone stationary phases at 260°C. 

Ascorbic acid was silylated by means of HMDS and N-trimethylsilylacetamide [532]. Whereas the former reagent provided two products the concentrations of which decreased within a rather short period of time, the latter provided satisfactory results. With a 15-fold excess of the reagent a uniform derivative was produced at room temperature after reaction for 4 h and the results were reproducible. XE-60 and SE-30 silicone stationary phases were used at 135 and 170°C, respectively. 

Becerra, M. R. Fernandez-Sanchez, E. Fernandez-Torres, A. Garcia-Dominguez, J. A. Santiuste, J. M., "Evaluation of the Effect of the Cyanopropyl Radical on the Interaction of the Methylene Group with Silicon Stationary Phases," J. Chromatogr., 547, 269 (1991). 

Gas chromatography detectors are relatively easy devices to operate and maintain. Some have special foibles. The FID flame is ignited by a small heater filament situated close to the flame. Difficulty in flame ignition is frequently experienced and it is almost always because the flow rates of the three gases have not been properly adjusted to the values recommended for ignition by the manufacturer. The electrodes of the FID will become corroded with time. If there has been extensive use of silicone stationary phases, or silyl derivatives have... 

Nevertheless, the same precautions should be taken as those advised for the FED. If used with silicone stationary phases, or for the separation of silyl derivatives, the electrodes and jet will also become covered with silica and must be cleaned. In general, problems with detector electronics are very rare indeed. Contemporary detector electronics are almost exclusively solid state and consequently, if the... 

The 50% phenyl-substituted silicone and 30% biphenyl-substituted silicone stationary phases are moderately polar and contain polarizable aromatic rings that exhibit induced dipoles in the presence of dipolar solutes such as alcohols, phenols, amines, nitriles, ketones, and so forth. They give selectivity with-... 

The equipment used for this work consisted of a Hewlett-Packard 5710A GC, with on-coluitm injection, directly coupled to a VG7070E medium resolution double-focusing mass spectrometer. The GC coluitm employed was a 60 m fused silica capillary colurrm coated with a cross-linked methyl silicone stationary phase, DB-1. The initial temperature of the colurrm was 30°C, and after 4 minutes, the temperature was linearly programmed at 8°C/min to 270°C, and held at this final temperature for 15 minutes. The mass spectrometer was operated in the electron impact (El) mode, and the mass range of 20-700u was scanned once a second. The mass spectrometer was linked to an Incos data system which stored the acqnired mass spectra, and allowed these to be compared to the EPA/NIH Mass Spectral Data Base to assist with the identification of compounds detected. 

Fig. 4. Chromatogram of separation on a silicone stationary phase of methyl esters of trifluoro-acetylated amino acids of hydrolysate of human fingernail. Sorbent silicone stationary phase. Temperature programme A, 100°C, isothermal B, heating from 100°C at 1.5°C/min C, heating from 116.5°C at 4°C/min D, 140°C, isothermal E, heating from 140°C at 6°C/min to 210°C. Peaks 1 = alanine 2 = valine 3 = glycine 4 = isoleucine 5 = threonine 6 = leucine 7 = norleucine 8 = internal standard 9 = proline 10 = asparagine 11 = glutamine 12 = phenylalanine 13 = tyrosine 14 = lysine. From ref. 13.

As an example of a clear improvement in separation we can cite the data on the retention of steroids on a non-polar silicone stationary phase, SE-30, as presented by Heftmann [54]. Two monohydroxy-steroids, 5a-cholestan-3 3-ol and 5-cholesten-3 3-ol, have the same relative retention (2.85) on a column containing a non-polar stationary phase (internal standard cholestane), but the relative retentions of their trimethylsilyl derivatives are 2.60 and 2.55 and those of their chlorodichloroacetates are 3.79 and 3.62, respectively. The relative retention times of 3a-hydroxy-5a-androstan-17-one and 3j3-hydroxy-5a-androstan-17-one are similar at 0.96 and 1.00, respectively, whereas those of their TMS ethers are 0.46 and 0.61, respectively. 

When CFD methods are used, after the reactions for the protection of functional groups that interact (adsorption, reaction, catalysis) with the sorbent and the apparatus have been accomplished, less polar derivatives are formed and, as a rule, these can be successfully separated by using a non-polar thermally stable (e.g., silicone) stationary phase. At the same time, however, especially when compounds of high molecular weight are separated, in a number of instances difficulties arise in separating the derivatives obtained, because the individual characteristic features of a compound, after the protection of its functional groups, are in fact often blurred. It is therefore expedient to use capillary columns as often as possible in analysing derivatives [85—88]. 

Not only complexes but also metal salts that complex with the compounds to be separated can be used as selective complexing stationary phases. For example, Phillips [91] described the use of zinc and copper stearates and nickel oleate for the selective separation of amines. The retentions of aliphatic amines decrease in the order primary > secondary > tertiary. The separation of 7-picoline and 2,6-lutidine on a zinc stearate column is possible if the column efficiency is only 4 theoretical plates and the column is 1 cm long. To effect this separation on a non-selective silicone stationary phase a column with an efficiency of 250,000 theoretical plates is required. Some amines (e.g., ethanolamine... 

The chromatographic separation of chlorinated pesticides has been performed with packed columns until the late 1970s to early 1980s, the liquid phases most commonly used being siliconic phases. The operating isothermal temperature was in most cases around 200°C. Nowadays for the GC analysis of chlorinated pesticides fused silica capillary columns are exclusively used. The nonpolar siliconic stationary phases (methylphenylsilicon polymer) are the most frequently used. 

Royal Society of Chemistry, 1981. Analytical Methods Committee, Application of gas-liquid chromatography to the analysis of essential oils, Part VIII. Fingerprinting of essential oils by temperature-programmed gas-liquid chromatography using methyl silicone stationary phases. 

Analysis for Underivatized Theophylline by Gas Chromatography on Silicone Stationary Phase, SP-2510-DA... 

R. A. DeZeeuw, J.-P. Franke, H. H. Maurer, and K. Pfleger, eds., Gas Chromatographic Retention Indices ofToxicologically Relevant Substances on Packed or Capillary Columns With Dimethyl-silicone Stationary Phases, VCH, Weinheim, Germany, 1992. 

BEC Becerra, M.R., Femandez-Sanchez, E., Femandez-Torres, A., Garcia-Dominguze, J.A., and Santiuste, J.M., Evaluation of the effect of the cyanopropyl radical on the interaction of the methylene group with silicone stationary phases, J. Chromatogr., 547, 269, 1991. 

Fatty acid Silicone Stationary phase Carbowax Silar 5CP CP-SM84... 

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