CHARACTERIZING EFFECTS OF CATIONIC SURFACTANT ON ELECTRO-OSMOTIC MOBILITY AND ANION MIGRATION IN CAPILLARY ELECTROPHORESIS

Abstract

The analysis of anions by capillary electrophoresis (CE) with bare silica capillary often uses cationic surfactant to modify the electro-osmotic mobility (EOM) to ensure anions migrating to anode and being detected. The effect of cetyltrimethylammonium bromide (CTAB) concentration in phosphate background electrolyte (BGE) with various ionic strength and pH on the migration of analytes was investigated and reported. A concentration of 0.08 mM CTAB in the BGE starts to reverse cathodic EOM into anodic EOM, and a concentration of 0.30 mM CTAB in the BGE maximizes anodic EOM. Lower EOM is obtained in BGE of higher phosphate concentration while the CTAB concentration and pH are kept constant. Under conditions of constant CTAB and phosphate concentration, higher cathodic EOM was obtained in the BGE of higher pH and lower anodic EOM was obtained in the BGE of higher pH. Although the effect of CTAB concentration, pH, and phosphate concentration on the migration of aromatic anions is complex, the result indicates that the most rapid and effective separation for the anions can be achieved by using a BGE with 0.20 mM CTAB. Furthermore, the relationship between the electrophoretic mobility of anions and the CTAB concentration can be used to determine the critical micelle concentration of cationic surfactant.