Dimethyl polysiloxane capillary

GC-MS, 5% phenyl/95% dimethyl polysiloxane capillary column. Carrier gas He... 

GC column 5% Diphenyl-95% dimethyl polysiloxane-fused silica capillary (30m x 0.25 mm i.d. 0.25-pm film thickness)... 

GC-MS Analysis. The dimethylated anacardic acids were analyzed by gas chromatography-mass spectrometry (gc-ms). All analyses were performed in the El mode, using a Kratos model MS-25 mass spectrometer, with a 30m x 0.53mm RTX-5 (Restek Corp., cross bonded 95% dimethyl-5% diphenyl polysiloxane) capillary column with a temperature program of 250-280°C at 5°C/minute. 

Figure 2. GC-MS total ion chromatogram of the total lipid extract of a potsherd recovered from the fill of a medieval ditch. Peak identities I4-T8, 20 and 25 are saturated fatty acids (as TMS ester derivatives) containing 14-18, 20 and 25 acyl carbon atoms respectively 16 1,18 1 and 20 1 are mono-unsaturated fatty acids (TMS esters) containing 16,18 and 20 acyl carbon atoms, respectively D32, D34 and D36 are diacylglycerols (TMS ethers) containing 32, 34 and 36 acyl carbon atoms, respectively 44, 46, 48, 50, 52 and 54 are triacylglycerols containing 44, 46, 48, 50, 52 and 54 acyl carbon atoms, respectively 1 is nonacosane, 2 is nonacosan-15-one, and 3 is nonacosan-lS-ol (TMS ether). Analyses were performed using a I2m x 0.22 mm i.d. BP-1 coated (immobilized dimethyl polysiloxane, 0.1 flm film thickness) fused-silica capillary. After on-column injection and a 2-minute delay the GC oven temperature was programmed from 50 to 350 °C at 10°C/min. (Reproduced from reference 1183] with permission).

Gas chromatography possesses inherent advantages that make it particularly attractive for the characterization and quantitative analysis of terpene mixtures. These include high separation efficiencies, short residence times in the chromatographic column, and the use of an inert atmosphere during analysis, the lack of azeotropes, and applicability to very small samples. In most cases capallaiy columns with dimethyl polysiloxane (methyl silicone) nonpolar and Carbowax 20M pwlar phases are used. Carbowax 20M phases include DB Wax, BP-20, PEG 20M and HP 20, while methyl silicone phases include SE-30, SF-%, OV-1, OV 101, BP 1, CPSIL 5CB, SP 2100, DB 1, DB 5 and HP 1 (Davies, 1990). Among these fused-silica capillary GC columns, DB 1 or DB 5 and CPSil 5 are usually preferred. 

Figure 2 Gas chromatographic separation of hydrocarbons found in an urban air sample. Open capillary, 0.32 mm i.d. x 60 m length stationary phase, DB-1 (dimethyl polysiloxane) film thickness, 0.25 pm carrier gas, helium temperature programme, 5°C isothermal for 3 min, 5-50°C at a rate of 3°C min 50-220°C at a rate of 5°C min detector, flame ionization. With this method, a total of 142 hydrocarbons could be separated and identified 128 of them were found in the urban air sample. (After Ciccioli P, Cecinato A, Brancaleoni E, Frattoni M, and Liberti A (1992) Use of carbon adsorption traps combined with high resolution GC-MS for the analysis of polar and nonpolar C4-C14 hydrocarbons involved in photochemical smog formation. Journal of High Resolution Chromatography 15 75.)...

N,0-bis(trimethylsilyl)trifluoroacetamide are separated with a 30-m capillary column coated with 100% dimethyl polysiloxane phase. 

Schematic structures of both a dimethyl polysiloxane and a polyethylene glycol liquid phase were given in Chapter 4. There is, however, one difference between packed column and capillary column liquid phases capillary column phases are extensively cross-linked. By heating the freshly prepared capillary column at high temperatures (without column flow) the methyl groups form free radicals which readily cross-link to form a more stable, higher molecular weight gum phase. There is even some chemical bonding with the silanol groups on the fused silica surface. These cross-linked and chemically bonded phases are more temperature stable, last longer and can be cleaned by rinsing with solvents when cold. Most commercial capillary columns are cross-linked.

Sample injecticms for the split-splitless GC inlet were realized using the Hamilton microliter syringes in splitless mode. The typical sample volume was 1 pi, splitless time 1.00 min and injector temperature 200 °C. All of the samples were separated through 50 m capillary column HP Ultra-1 (100% dimethyl-polysiloxane) with 0.2 mm i.d. and 0.33 pm film thickness. The carrier gas was cleaned helium 4.6 purity with constant flow of 0.5 ml.min EPC controlled, for obtaining Cl spectra methane 5.5 purity as reagent gas was used. The GC oven temperature was 50 °C for 1 min, then programmed with the rate of 10 C.min to 275 C. MSD interface temperature was 280 C, in the case of CIMS measurment only 250 C. 

Permethrinic acid has two enantiomer pairs and four isomers (2" = 4) (Table B33, Appendix B). The acid leaving group for permethrin, cypermethrin, and cyfluthrin is permethrinic acid. The structure of this acid is given in Table 3. Angerer and Ritter (1997) separated the methyl esters of cis- and trans-permethrinic acid on a polysiloxane capillary column by GC (Table C18, Appendix C). The carboxylic acids of several of these pyrethroids were also listed as trans- or cw-3-(2, 2-dichlorovinyl)-2, 2-dimethyl cyclopropane carboxylic acid. The acids may be separated on a CHIREX phase 3005 column (Phenomenex, 2320 W 205th Street, Torrance, CA 90501) by HPLC. 

GC column A capillary column of intermediate polarity can give adequate resolution of isomers as well as unsaturated compounds. Many such columns are commercially available. These include 105 m long x 0.53 mm ID, Rtx-502.2 60 m long x 0.75 mm ID, VOCOL 60 m long x 0.53 mm ID, DB-62 or equivalent. Other capillary columns include 95% dimethyl-5% diphenyl polysiloxane coated columns, such as DB-5, SPB-5, Rtx-5, AT-5, or equivalent. These columns are also suitable for separation of a number of nonhalogenated organic compounds of intermediate polarity. 

Gas chromatography was equipped with a DB-5, 95% dimethyl 5% diphenyl polysiloxane—bounded capillary column. It was combined with a mass spectrometer (ITS 40 Finnigan Matt). 

High-resolution gas chromatography (HRGC) has been widely applied for the determination of PCB contents in water samples [112]. PCBs can be separated on a 30-50 m fused silica capillary column with various chemically bonded stationary phases. Table 20.6 shows combinations of column lengths, stationary phases, oven temperature programs, and detectors. Polysiloxane (95% dimethyl-5% phenyl) is the most widely used stationary phase, although 5% diphenyl polydimethylsiloxane, 7% methyl-7% cyanopropyl-phenyl polysiloxane, 95% dimethyl 5% phenyl polysiloxane, 50% phenyl-methyl-polysiloxane are also used. 

Madani et al. provided the first detailed description of capillary columns where polysiloxanes were immobilized by hydrolysis of dimethyl- and diphenylchlorosi-lanes (77,78). Interest increased when Grob found that the formation of cross-linked polysiloxanes resulted in enhanced film stability (79). Blomberg et al. illustrated in situsynthesis of polysiloxanes with silicon tetrachloride as a precursor, followed by polysiloxane solution (80,81). Since then, various approaches to cross-linking have been investigated. These include chemical additives such as... 

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