PREPARATION OF DEACTIVATED METAL CAPILLARY FOR GAS-CHROMATOGRAPHY

Research was conducted to prepare a deactivated metal (stainless-steel) capillary that is physically tough and thermally stable compared with a fused-silica capillary. A key step in the preparation is the formation of a silicon layer by the thermal decomposition of monosilane. The silicon formed on the metal surface is assumed to exist as Large grains compared with that on the glass surface. Activation of metal capillary was observed, which is assumed to be due to the migration of silicon grains on the metal surface during the heating test of the capillary, thus exposing the metal surface. Such a phenomenon was not found with a glass capillary treated with monosilane. These observations suggest that the problem comes from the wettability of the metal surface with silicon. The problem was solved by oxidizing the metal surface prior to the monosilane treatment. As a consequence, it became possible to prepare a deactivated metal capillary (DMC) thermally stable even above 400 degrees C. A column coated with a commercially available gum-like liquid phase could not withstand continuous heating at 280 degrees C. On the other hand, a column coated with dimethylpolysiloxane by the in situ (in the capillary) condensation of oligomer prepared from dimethyldichlorosilane showed excellent thermal stability: the column withstood continuous heating above 400 degrees C and also repeated heating by programming up to 450 degrees C. Various advantages of DMC over a fused-silica capillary (FSC) were also made clear. Hence DMC, as a metal capillary of the second generation, should replace FSC.