The preparation of immobilized polysiloxane coated on packings materials for high-pressure gas chromatography

Summary In high pressure gas chromatography efficient columns can be packed by the slurry packing technique. However, polysiloxane stationary phases like OV 101 and OV 3 dissolve in the packing liquids. In order to make them suitable for slurry packing these stationary phases have to be made insoluble. This immobilization is achieved by bonding the stationary phases to the surface by means of a high temperature treatment. Successive layers are applied by recoating and are immobilized by a cross-link reaction. A range of loading percentages from 4 upto 20 by weight could be prepared in this way. On the evaluated columns compounds like butanol and dioxane elute as rather symmetrical peaks with the correct values for the retention index, indicating the absence of adsorption effects. Efficiency is good and bleeding rate is low. The columns could be successfully used in the analysis of turpentines.     

Column packing for gas chromatography containing immobilized poly(ethylene glycol) stationary phase

Summary Carbowax 20M poly(ethylene glycol) stationary phase was immobilized on Chromosorb W by cross-linking with pluriisocyanate. The properties of the prepared packing material were investigated. Column efficiencies of 10,960 and 7,510 theoretical plates/meter were obtained for n-pentadecane and 1-heptanol, respectively.     

Dicyanobiphenyl polysioloxane stationary phases for capillary column gas chromatography

Summary The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes. Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C. The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds.     

Evaluation of smectic biphenylcarboxylate ester liquid-crystalline polysiloxane stationary phases for capillary column gas chromatography

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.     

Liquid crystal stationary phases for gas chromatography and supercritical fluid chromatography

Novel monomeric and polymeric liquid crystalline compounds were synthesized as stationary phases for gas chromatography (GC) and supercritical fluid chromatography (SFC). Monomeric liquid crystalline compounds were used in packed column gas chromatography for the separation of isomeric aromatic compounds and insect sex pheromones. Liquid crystalline polymers possess long nematic ranges and a uniform coating was easily achieved in glass and fused silica capillaries, which could stand temperatures up to 250°C in GC and pressures of 200 MPa at 160°C in SFC. The columns provide excellent selectivity and resolution for fused ring aromatic compounds such as the isomers anthracene and phenanthrene or triphenylene and chrysene.     

Liquid-crystalline stationary phases for gas chromatography

Physico-chemical properties of new liquid-crystalline stationary phases (LCSPs) for gas chromatography are reviewed. The mechanism of chromatographic separation on liquid-crystalline stationary phases is discussed and examples of analyses of complex mixtures of organic compounds using capillary and packed columns are given.     

On-line multidimensional chromatography using packed capillary liquid chromatography and capillary gas chromatography

The introduction of selected fractions from a liquid chromatograph into a gas chromatograph has been described; however, analyses were performed by off-line experiments requiring collection and reinjection of the separate fractions or by on-line procedures where disadvantageously, only a fraction of the separated peak or a well resolved component in a mixture could be introduced into a gas chromatograph. This disadvantage is overcome by the apparatus and method described in this paper, which utilizes a multidimensional chromatography system employing a high efficiency, packed capillary LC column coupled on-line to a capillary gas chromatograph. The liquid chromatograph (so designed) can act as a highly efficient clean-up or chemical class fractionation step prior to introduction into the gas chromatograph, significantly reducing sample preparation times in many applications. Thus minor components in a complex matrix can be determined without prior sample clean-up, an example of which is the determination of polychlorinated biphenyls in a complex hydrocarbon matrix.     

Polarizable biphenyl polysiloxane stationary phase for capillary column gas chromatography

A crosslinkable biphenylmethylpolysiloxane stationary phase was synthesized for capillary column gas chromatography and compared with methyl, phenyl, and cyanopropyl polysiloxane stationary phases for the separation of isomeric polycyclic aromatic compounds. While the new phase gave similar separations of nonpolar isomers when compared to the nonpolar phases, separations of polar isomers were greatly improved because of the induced polarity of the biphenyl group of the stationary phase by the solute molecules. This polarizable stationary phase offers a unique selectivity which is not available in other stationary phases.     

The preparation of non-extractable methylphenylpolysiloxane stationary phases for capillary column gas chromatography

Summary The synthesis of methylphenylpolysiloxane polymers and their use in the preparation of crosslinked, non-extractable stationary phases for fused-silica capillary columns are described. By preparing more viscous phenyl-containing polymers than are commercially available, stationary phase films of these polymers could be efficiently coated on fused-silica capillary columns and stabilized by a free radical crosslinking mechanism using peroxides. Four methylphenylpolysiloxane polymers containing different phenyl concentrations were prepared. These included three polymers containing 50% phenyl and one polymer containing 70% phenyl. Two of the 50% phenyl polymers had one phenyl and one methyl group attached to each silicon atom. One of these also had 1% vinyl incorporated. The third 50% phenyl polymer was synthesized in such a way that one half of the silicon atoms had two phenyl groups attached while the rest contained dimethyl groups. The 70% phenyl polymer also had 4% vinyl incorporated. Due to the intrinsic thermal stability of these phenyl phases and the enhanced film stability achieved by crosslinking, the 70% phenyl phase could be utilized up to 400 °C. Using the methods described in this paper, highly efficient and thermally stable fused silica capillary columns coated with crosslinked methylphenylpolysiloxane stationary phases can be successfully prepared.     

Comparison of packed and capillary columns for quantitative gas chromatography of triglycerides in milk fat

Summary Quantitative gas chromatography of triglycerides in conjunction with established triglyceride formulae can be used to determine various milk fat parameters. Since the evaluation of, for example, iodine number or content of non-milk fats (foreign fats) in milk fat requires only the separation of triglycerides by carbon number and since repeatabilities, especially of the highboiling triglycerides, have been less acceptable with capillary columns in the past, packed columns have been used exclusively. There is, however, an increasing demand for the use of capillary instead of packed columns and to that end the present investigation has been carried out. To achieve a suitable resolution, with this particularly exacting high-temperature application, a short 5 m capillary column of extreme temperature stability has been used. As well as modification of various analytical conditions different injection techniques have been investigated. On-column, PTV and split injection were compared with regard to repeatability. The cold-on-column injection technique was found to produce the best results, being comparable to the excellent precision of a packed column. Thus, a method is now available by means of which the determination of milk fat parameters by the triglyceride formulae, such as the amount of foreign fats in milk fat, can now be carried out with a standardized capillary column.     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Quantitative analysis of apolar polysiloxane phases in large-bore capillary columns

Summary A technique is described for determination of the amount of bonded phase in commercial columns. It is adapted to the determination of the real nature and the thickness of a siloxane bonded film. Ten-centimeter samples of column are used. The method is tested for large-bore capillary columns. Applications to kinetic studies are suggested.     

Cold trap/reinjection interface for two-dimensional gas chromatography

The construction and evaluation of an interface for two-dimensional gas chromatography is described. The interface consists of commercially available components and is attachable to available gas chromatographs without any major modifications. The interface has been constructed so as to permit “heartcutting” as well as solute band concentration. Trapping is performed in a simple cold trap of fused silica. Flow switching is accomplished by Deans switching. Factors of the over-all chromatographic performance are examined.     

Glass capillary gas chromatography of chlorinated methyl acetates,propanoates and butanoates on Carbowax 20M and SE-30 columns

Summary The gas chromatography of all chlorinated methyl acetates, methyl propanoates and methyl mono- and dichlorobutanoates has been studied on Carbowax 20M and SE-30 glass capillary columns under various running conditions. The order of elution on a non-polar column was largely determined by the boiling point of esters, whereas on a polar column it was much influenced by the structure of compounds. Complete separation of the combined mixture of all 27 compounds could not be achieved, however, methyl 3,3-dichlorobutanoate was the only ester overlapped on both columns in spite of the various column temperatures used. The best separation of the mixture was on Carbowax 20M with a temperature program from 50°C at 8°C/min, isothermal running conditions leading either to poor separation of volatile components or long analysis time and broad peaks of higher chlorinated esters. The relative retention times for compounds at the various column temperatures are given and the retention order on a polar and on a non-polar column discussed.     

Preparation and chromatographic characteristics of calix[4]arene polysiloxane as stationary phases for capillary gas chromatography

Summary Two new kinds of calix[4]arene derivatives, 5, 11, 17, 23-tetra-tert-butyl-25,27-bis(isopropylcarbamoyl-methoxy)-26,28-diundecenyloxy calix[4]arene (C[4]A) and 25,27-dibutoxy-5, 11, 17, 23-tetra-tert-butyl-26,28-diundecenyloxy calix[4]arene (C[4]B0, are prepared and then are polymized by two different processes. Three calix[4]arene polysiloxane stationary phases for capillary gas chromatography are obtained. Their chromatographic characteristics, including column efficiency, polarity, selectivity, glass-transition temperature and thermal stability are studied. Retention mechanisms are also discussed.     

A novel ionic liquids grafted polysiloxane for capillary gas chromatography

A new ionic liquids grafted polysiloxane used as stationary phase for capillary gas chromatography(CGC) is described.The stationary phase of 1-vinyl-3-hexylimidazolium hexafluorophosphate anchored to polysiloxane(PMHS-[VHIm][PF_6]) was synthesized, characterized and coated onto capillary columns by static coating.The results show that the present stationary phase exhibits a very good chromatographic resolution and selectivity for Grob test mixture and alcohols with baseline resolution and symmetry peaks....