Deactivation of metal capillaries for gas chromatography

Abstract

A novel method to deactivate metal (stainless steel) capillaries for gas chromatography was developed using perhydropolysilazane (PSZ). A metal plate was used first to examine the nature of the pyrolyzed PSZ. The Auger analysis demonstrated that the PSZ layer pyrolyzed under a nitrogen atmosphere was composed of Si and N, but the layer pyrolyzed in air was composed of Si and O, indicating that the pyrolysis of the PSZ layer in air gives a silica layer. It was observed from scanning electron microscopy that the pyrolysis of PSZ on a metal plate gave a silica layer as a smooth film. Contact angle measurement revealed that the surface free energy and its components of the pyrolyzed PSZ in air were almost the same as those of silica. The interface between the stainless steel and coating silica layer was tough enough to endure the bending treatment. Deactivation of capillaries with PSZ was first examined using glass capillaries. A polarity test chromatogram showed tailing for the polar solutes, suggesting that the inner surface of capillaries is coated with silica layer rich in silanol groups after the pyrolysis of PSZ. Deactivation was accomplished by treating further with octamethyltetrasiloxane (D4), showing that PSZ treatment followed by D4 treatment is efficient as a deactivation method. Then, deactivation of metal capillaries was examined using the same procedure. It was found that deactivated metal capillaries were obtained successfully by the PSZ coating and pyrolysis followed by D4 treatment. It was also observed that pretreatment including acid washing and oxidation is recommended to obtain deactivated metal capillaries with high reproducibility.