In this study the possibility of operating a wide‐bore column with an inner diameter of 530 μm at vacuum conditions was investigated as a route towards fast gas chromatography. High analysis speeds can be obtained as a result of the sub‐ambient pressure conditions present in the column, and the consequently high diffusion coefficient of the solute in the mobile phase. The advantage of using a wide‐bore column is the high sample capacity. To enable vacuum operation through coupling a wide‐bore column to a mass spectrometer, three types of restricting the column flow were investigated. The first method uses a narrow bore pre‐column (60 cm length×100 μm i.d.), the second method relies on the use of a tapered on column supercritical fluid chromatography restrictor (SFC‐restriction), whereas the third method makes use of a micro‐injection valve. It was concluded that the best performance was obtained using the narrow‐bore column restriction and the SFC‐type restriction. Analysis examples in the seconds‐ and minutes‐range are shown, with peak‐widths ranging from 0.1 to 2 seconds at half height. It was concluded that with a film‐thickness above 1.5 μm, the advantage of the increase in analysis‐speed due to low pressures is nullified due to retention time increase on a thick film column. © 2001 John Wiley & Sons, Inc. J Micro Sep 12: 613–622, 2000

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The effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by 29Si and 13C CP‐MAS NMR. Fumed silica (Cab‐O‐Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material. Hexamethyldisilazane (HMDS) and 1,2‐diphenyl‐1,1,3,3‐tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl‐ and dimethylphenylsilyl surface groups respectively at lower temperatures (< 350°C and <250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The 13C NMR and GC‐MS of the reaction products showed that with DPTMDS, the formation of two Si‐O‐Si links is accompanied by a loss of phenyl groups rather than of methyl groups. After the Cab‐O‐Sil had been dried over P2O5, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si‐O‐Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries.

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