Control of separation selectivity and electroosmotic flow in nonaqueous capillary electrophoretic separations of alkali and alkaline earth metal ions

Factors affecting the separation selectivity and electroosmotic flow (EOF) for the separation of alkali, alkaline earth cations, and ammonium ion in nonaqueous systems were evaluated. The nature of electrolyte anion (chloride, perchlorate, and acetate) and solvent (methanol-acetonitrile mixtures) had important effects on the EOF in acidic conditions. Evidence was observed for ion adsorption (protons and anions) on the silica surface and for ion-interactions in the electrolyte; both effects could be used to control the direction and magnitude of the EOF. Relative to aqueous systems, unique separation selectivity was achieved for alkali and alkaline earth cations; ammonium and alkali cations were resolved from alkaline earth cations and potassium and ammonium ions were well separated. Calibration of all the cations gave linear curves in the range of 5X10(-4)-5X10(-5) mol/l; detection limits (indirect with imidazole) were in the range of 7x10(-6)-2x10(-5) mol/l. To evaluate this system, the separation of metal ions was examined for a brine solution and an aqueous soil extract sample.