Simultaneous Separation of Inorganic Ions and Neutral Organics on a Sol-Gel-Coated Capillary using Combined Capillary Zone Electrophoresis and Capillary Electrochromatography

Abstract

Capillary zone electrophoresis was combined with capillary electrochromatography to effect the separation of ionic and neutral organic mixtures. Sol-gel technology was used to coat the capillary wall with a silane-based stationary phase. An n-octyl phase was used for cation-organic mixtures and an octadecyl phase, which incorporated a quaternary ammonium group to effect electroosmotic flow reversal, was employed for anion-organic mixtures. Tetraethoxy silane was used as a spacer to control the density of stationary phase interactive groups. Some data on the optimum ratio of analyte-interactive group to spacer silane in the sol-gel reaction mixture was obtained. Mobile phases were mixtures of typical capillary electrophoresis run buffer and reversed phase chromatography constituents. In all cases, the analytes were separated both within and between classes, the ions exiting the capillary as a group before the neutral organics. Investigation of mobile phase methanol cosolvent and pH effects found that electrophoretic and chromatographic behavior in the mixed mode system was what would be observed in a single mode separation, demonstrating the independence of the two modes. Separation of ions and neutrals in a red wine and multivitamin is demonstrated.