Nonpolar polysiloxane phases

The majority of insect and mammalian pheromones are small and relatively simple molecules with low polarity. Nonpolar polysiloxane phases such as 100% polysiloxane or 5% polyphenylmethyl siloxane are the preferred column for pheromone research due to a broad range, thermal stability, and long lifetime. Five per cent (phenyl)methylpolysiloxane columns were used in the identification of dodecenyl acetate and dodecenol, the sex pheromones of the citrus fruit borer, and anisole, the sex pheromone of the scarab beetle. A 100% polysiloxane column was used in the analysis of dodecenyl acetate, the female sex pheromone of the Asian elephant. 

Viscosity of the film of stationary phase after deposition under the thermal conditions of GC proved to be an important consideration. Wright and coworkers (103) correlated viscosity of a stationary phase with coating efficiency and stability of the coated phase. The results of their study supported the experimental success of viscous gum phases, which yielded higher coating efficiencies and had greater thermal stability than did corresponding nonviscous counterparts. The popularity of the nonpolar polysiloxane phases is due in part to the... 

Because of the general nature of the descriptors used in the two models, no attempt was made to precisely interpret their physical significance. However, an intuitive explanation may be proposed. The column used in this study consisted of a SE-30, dimethyl-polysiloxane stationary phase. This relatively nonpolar stationary phase typically takes advantage of dispersive interactions as opposed to dipole-dipole, dipole-induced-dipole, or acid-base interactions. These dispersive interactions are, in turn, loosely related to the bulk properties of the solute molecules (e.g., boiling point). All of the descriptors utilized in this study may be generally classified as bulk property descriptors. We can... 

Popov et al measured the relative retention volumes and retention indices for silicon tetrachloride, methyltrichloro- and dimethyldichloro-silane, phosphorus trichloride and phosphorus oxychloride at 50 0 on the following stationary phases (each in a concentration of 20% on the support) Vaseline oil, polysiloxane liquids VKZh-94, PFMS-2 and DS-701 fluorosilicone oil 169, dinonyl phthalate and dibutyl phthalate. The retention index for phosphorus oxychloride increased with increase in the polarity of the stationary phase that for silicon tetrachloride remained practically constant. The maximum difference in retention volume was obtained on a nonpolar stationary phase for phosphorus trichloride and the chloro-silanes, and on a polar stationary phase for phosphorous oxychloride and the chlorosilanes. 

The retention index of 657 for benzene on poly(dimethylsiloxane) in Table 24-3 means that benzene is eluted between hexane (7 = 600) and heptane (7 = 700) from this nonpolar station-aiy phase. Nitropropane is eluted just after heptane on the same column. As we go down the table, the stationary phases become more polar. For (biscyanopropyl)09(cyanopropylphenyl)0l-polysiloxane at the bottom of the table, benzene is eluted after decane, and nitropropane is eluted after -Cl4H30. 

Haken has considered the applicability of "Rohrschneider/ McReynolds constants" for the classification of stationary phases for the separation of fatty esters (13). He concluded that the approach was limited since the measurements used to determine the aforementioned "constants" are made at 100°C and most fatty acid methyl ester separations are carried out at about 200°C. He had previously shown significant variation in the, what will now be called, Rohrschneider/McReynolds coefficients, with temperature (14). Polar polysiloxanes such as XF-1150 demonstrated greatest variability in the coefficients and nonpolar types such as SE-30 demonstrated least variation. Supina pointed out that the X factor in the McReynolds coefficients should be indicative of extent of interaction with olefinic substituents (15). Figure 9.5 demonstrates the utility of this approach the 18 3 and 20 0 methyl esters are used as markers for the consideration of... 

Typically, FRs are determined on nonpolar or semipolar columns such as 100% methyl polysiloxane type (DB-1) and 5% phenyl dimethyl polysiloxane type (DB-5, CP-SU 8, and AT-5). Also semipolar phases, such as 8% phenyl-polycarborane-siloxane HT-8, 14% cyanopropylphenyl 86% dimethyl polysiloxane (CP-SU 19, HP-1701, and DB-1701) have been utilized. 

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. 

The best separations of polyols have been achieved on mixed phase packings, which combine the high resolving capacity of the polar phase with the stability of the nonpolar phase. Reported stationary phases are 2-10% EGSS-X (ethylene glycol succinate copolymerized with dimethyl polysiloxane) or ECNSS-M (ethylene glycol succinate copolymerized with cyano-ethyl methyl polysiloxane) on uncoated adsorbent from diatomite, acid washed, and dimethylchlorosi-lane-treated or uncoated adsorbent from diatomite acid-washed and silanized, 3% XE-60 (poly(methyl cyanopropyl siloxane)) on uncoated adsorbent from diatomite acid-washed and silanized, GP 3% SP-2340 (poly(dicyanopropyl siloxane)) on diatomite support and many other combinations. 

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.)...

The liquid stationary phases used with capillary columns are similar to those used in packed columns. The most common stationary phases are polysiloxanes (silicones) that contain various substituents that modify the polarity of the phase. Polydimethyl siloxane (methyl silicone) is nonpolar. Replacing methyl groups with increasing numbers of phenyl substituents increases the polarity of the silicone. For example, J W DB-1, or a similar stationary phase sold by other companies, has the same properties as methyl silicone (SE-30 or DC-200) and is used with nonpolar... 

A variety of agents and procedures have been explored for deactivation purposes (60-74). For subsequent coating with nonpolar and moderately polar stationary phases such as polysiloxanes, fused silica has been deactivated by silylation at elevated temperatures, thermal degradation of polysiloxanes and polyethylene glycols, and the dehydrocondensation of silicon hydride polysiloxanes (71,75-79). 

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