High-purity fused-silica capillary columns for gas chromatography

Abstract

High-purity fused-silica capillaries (made of SiO 2 of 99.9999% or higher purity, containing less than 1 ppm of hydroxy groups and metal oxides) have been evaluated for gas chromatographic applications. Various types of conventional glass capillary column were compared for inertness, and untreated high-purity fused-silica capillary columns were found to be the most inert. Untreated fused-silica capillary columns were compared with those deactivated with PEG-20M, using the Grob test mixture and a test mixture containing primary amines. Untreated fused-silica capillary columns coated with methylpolysiloxane (OV-101) showed some activity after coating, but, after conditioning at 280–350°C, they showed almost the same degree of inertness as the deactivated columns. In quantitative analysis of highly polar compounds containing a primary amine, the untreated fused-silica column showed no adsorption in the low concentration range of 0.1 ng for 2,6-dimethylphenol and dicyclohexylamine, 0.3 ng for octanol, and 2 ng for primary amine (laurylamine). In order to exaḿine the stability and service life in high-temperature operation, the heights equivalent to a theoretical plate (HETPs) before and after 550 h of continuous operation at 280°C column temperature were compared using an untreated fused-silica capillary column. The change inHETP was only 30%, and the chromatograms of polar compounds showed no significant difference. An untreated high-purity fused-silica capillary column coated with methylpolysiloxane (OV-101) ensured better stability and almost the same degree of inertness, in high-temperature operation, compared with the same column deactivated with PEG-20M.