J. Buijten

Peroxide-initiated in situ curing of silicone gums for capillary column gas chromatography

Abstract The combination of leaching, silanization with cyclic siloxanes and peroxide-initiated in situ vulcanization of silicone stationary phases for gas chromatography gives capillary columns that show very high efficiencies, very low adsorptivity as reflected by stringent tests and very high efficiencies, very low adsorptivity as reflected by stringent tests and very high stability, e.g., low bleeding rates. Such columns have been prepared using AR-glass and fused silica as the supports and SE-30, SE-52, SE-54 and polar OV-215 as stationary phases. The versatility of these columns is demonstrated by the analysis of underivatized drugs, barbiturates and tricyclic antidepressants. The separation of aqueous solutions is also described.

Cyanosilicones as stationary phases in gas chromatography : II. Gum and rubber phases on fused silica

Abstract The presence of cyano groups in the stationary phase may provide useful selective interactions during separation. In capillary gas chromatography, the full utility of such interactions will be evident when the columns show high efficiency, good deactivation, high thermal stability and reproducibility in retention characteristics. Columns that fulfil these requirements were prepared. Fused silica capillaries were treated with hydrochloric acid, silanized at a high temperature with cyclic cyanopropylsiloxane and statically coated with cyanopropylsilicone gum, which was finally immobilized by in situ cross-linking. Vulcanization is normally inhibited by cyanopropyl groups, but a certain percentage of tolyl groups in the gum made cross-linking possible. The usefulness of the cyanosilicone columns is demonstrated by the separation of several samples such as fatty acid methyl esters and pheromones.

Preparation of thermostable, phenyl silicone coated, glass capillary columns for separation of polyaromatic hydrocarbons

SummaryA procedure for the preparation of glass capillary columns coated with non-extractable phenyl polysiloxanes has been developed, the phenyl silicone being synthesised in situ in the column. The non-extractability can be explained in terms of a certain degree of crosslinking in the polymer and possibly also by some chemical bonding to the capillary glass wall. Rearrangement of the film at higher temperatures is counteracted by crosslinking in the phase. Column bleeding is thus decreased, and column efficiency is maintained even at higher temperatures. Such capillary columns showed suitable selectivities for separation of polyaromatic hydrocarbons, and the high temperatures necessary for these analyses could be attained.

Immobilization of polyethylene glycol in capillary columns for gas chromatography

Abstract Two methods are described for the immobilization of polyethylene glycol. Immobilization was achieved by reaction with methyl(vinyl)cyclopentasiloxane (V 5 ) and dicumyl peroxide or ethylene oxide. Fused-silica capillaries coated with V 5 -immobilized polyethylene glycol 40M could be used over a wide temperature interval, 30–300°C. Further, immobilization makes feasible the use of thick films. The utility of this column type is demonstrated by several examples. Especially notable is the excellent performance achieved with water solutions and also free acids.

Cyanosilicones as stationary phases in gas chromatography : III. Synthesis, characterization and evaluation

Abstract Methods for the reproducible synthesis of curable cyanosilicone stationary phases have been developed. Different paths of synthesis has been compared, and the influence of these on the phase properties examined. A series of phases having 33, 50, 60, 75% cyano substitution, respectively, was prepared, in a manner so as to avoid the formation of amides. The effects of the use of methyltolyl, bis(tolyl) and methylvinyl blocks and bis(dimethyl)silylarylene units on cross-linking of cyano-containing organosiloxanes were examined. These phases were characterized by various chromatographic, spectroscopic and thermal analytical methods. Columns coated with the phases were tested with respect to efficiency, activity and thermal stability. The usefulness of the phases for selective separations of fatty acid methyl esters is demonstrated both with standards and actual samples of different origins.

Crosslinked methylphenylsilicones as stationary phases for capillary gas chromatography

SummaryMethyl(phenyl)silicones offer useful selectivities when used as stationary phases in gas chromatography (GC). Such phases have, however, hitherto been of restricted importance in capillary GC due to the lack of phases having a viscosity high enough to ensure stationary phase film stability. Further, to utilize fully the possibilities of a methyl(phenyl)silicone capillary column, it must also possess high efficiency and a high degree of deactivation.In this work, the preparation of soda-glass capillary columns coated within situ cured methyl(phenyl) and methyl(tolyl)-silicones is presented. Vulcanization was made possible by the introduction of some vinyl substitution in the gum to be cured: tolyl-containing gums could be cured without the presence of vinyl groups. In addition, fused silica capillary columns coated with OV-1701 were prepared.The columns show a coating efficiency of above 80%, a thermal stability up to 320 °C and a high degree of deactivation. Their utility is demonstrated by the separation of samples containing polynuclear aromatics, antidepressants and some potent mutagens.

Use of poly(silarylene-methylphenylsiloxane) block copolymer as a thermostable stationary phase in capillary column gas chromatography

Preparation par copolymerisation du methyl (phenyl) dichlorosilane et du silarylene, et immobilisation in situ par le peroxyde de cumyle ou lozone

Ozone-initiated in situ cross-linking of non-polar and medium-polar silicone stationary phases for capillary gas chromatography

Abstract Non-polar and medium-polar stationary phases have been immobilized by an ozone-curing method in fused-silica capillaries. Phases such as SE-33, SE-54, OV-215 and methyl(tolyl)siloxanes (33% and 50% tolyl, respectively) could be cross-linked at room temperature. However, SE-30, SE-52, OV-1701, bis(cyanopropyl)methyltolylsiloxane (33% CN and 33% tolyl) and the methyl(phenyl)tolylsiloxanes (25% phenyl and 25% tolyl) required a higher temperature to obtain suitable immobilization. Tests made with columns coated with these ozone-immobilized silicones showed that non-polar and moderately polar phases were of high quality, and that the thermal stability was very good. Infrared spectra of the silicone phases showed no or a very weak absorption band in the region of 1700–1770 cm -1 .

Gas chromatographic—mass spectrometric analysis of compounds generated upon thermal degradation of some stationary phases in capillary gas chromatography

Abstract The thermal degradation products of some immobilized stationary phases for gas chromatography were studied. Column bleed products were analyzed by gas chromatography—mass spectrometry (GCue5f8MS); pyrolysis GCue5f8MS was also utilized in this study. The phases studied were: SE-30; methyltolyl silicone (33% tolyl); cyanopropyl (methyl)tolylsilicone (50% cyanopropyl, 25% methyl, 25% tolyl); Carbowax 40M. Cyanopropyl- and tolyl-substituted silicones were degraded mainly to three- to five-membered cyclics, but the cleavage of substituent groups seems to be relatively limited. the degradation products of Carbowax 40M consisted of homologous series of polyethylene glycol derivatives.

Some aspects of current techniques for the preparation of capillary columns for gas chromatography

Abstract Desirable column properties and their relation to different steps in column preparation are discussed. The properties of different capillary materials are compared, the different methods for high-temperature silylation, which are being used to achieve deactivation and wettability, are considered and the advantages of immobilized silicone stationary phases are described. Immobilization leads primarily to improved stationary phase film stability and this is of particular utility in connection with polar columns; some polar silicone gums have a high temperature coefficient of viscosity and may therefore be redistributed on a capillary surface at elevated temperatures, leading to deterioration in column performance. Immobilization very efficiently counteracts such an effect. Silicones containing cyanopropyl and phenyl substitution cannot readily be cross-linked. It is demonstrated that a convenient way to solve this problem is to include some tolyl substitution in the gum that is to be cross-linked.