SIMULTANEOUS SEPARATION OF AMMONIUM AND ALKALI, ALKALINE-EARTH AND TRANSITION-METAL IONS IN AQUEOUS-ORGANIC MEDIA BY CAPILLARY ION ANALYSIS

The simultaneous separation of the mono-, di- and trivalent cations NH 4+, K+, Na+, Li+, Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Ni2+, Zn2+, Cu2+ and C r3+ by capillary ion analysis was studied in a background electrolyte system composed of imidazole, 2-hydroxyisobutyric acid, 18-crown-6 and methanol. The effects of this system on the electroosmotic and electr ophoretic mobility were studied in detail. A competitive complexation between 2-hydroxyisobutyric acid and sulphuric acid was observed which determined the cation mobility. Applying a central composite design, a quantitative description of the electrophoretic behaviour of the ino rganic cations as a function of the system parameters was made and the optimum separation could be predicted. It was found in most instances that a linear model is sufficient for mobility modelling. Using a ful l factorial design, the main effects on the electroosmotic flow were e stimated and methanol was found to be the dominating factor. The appli cability of the capillary electrophoresis method was examined by separ ating ions in Chinese tea infusions. Five metal cations (K+, Na+, Ca2, Mg2+ and Mn2+) were detected. A limit of detection at the mu g/l lev el could be achieved using electromigration injection.