Improved resolution of inorganic anions in capillary electrophoresis by modification of the reversed electroosmotic flow and the anion mobility with mixed surfactants

The standard method for analysis of inorganic anions by capillary electrophoresis involves adding tetradecyltrimethylammonium bromide (TTAB) to the buffer to reverse the electroosmotic flow (EOF). The resolution achieved using this procedure is greatly improved by adding the zwitterionic surfactant, coco amidopropylhydroxydimethylsulfobetaine (CAS U) to lower the magnitude of the reversed EOF and alter the anion mobilities. In a mixed surfactant system, varying the ratio of TTAB to CAS U allows monotonic alteration of the EOF from fully reversed (TTAB alone) to near zero (CAS U alone). The total surfactant concentration (if greater than the critical micelle concentration) and buffer pH have minimal effect on the EOF. In addition, the anion mobilities can be altered to a minor degree by varying the ratio of TTAB to CAS U, which contributes to the improved anion resolution. The effect on the EOF of other surfactant systems involving CAS U and other cationic or anionic surfactants is also studied. (C) 1998 Elsevier Science B.V.