Capillary electrochromatography with novel stationary phases. I. Preparation and characterization of octadecylsulfonated silica.

A novel silica-based stationary phase was developed for use in capillary electrochromatography (CEC) at relatively high electroosmotic flow (EOF). The silica was first bonded with a relatively hydrophilic layer bearing strong sulfonic acid groups. To this charged polar sublayer, octadecyl functions were covalently attached to yield the nonpolar top layer. This novel stationary phase, referred to as octadecylsulfonated silica (ODSS), was packed in bare fused-silica capillaries or in capillaries with the same coating as the sublayer on the silica-based stationary phase. The resulting packed columns were evaluated in CEC using alkylbenzenes as the test model solutes. Good separations can be achieved in less than 8 min, much faster than when using a regular octadecyl silica capillary column. Due to the permanent negative charge provided by the sulfonated sublayer on both the capillary walls and the silica particles, the magnitude of the EOF remained more or less constant over a wide range of pH, and its magnitude can be conveniently varied by the applied voltage.