DETERMINATION OF CRITICAL MICELLE CONCENTRATION BY CAPILLARY ELECTROPHORESIS

Having previously reported [J. Chromatogr. A, 718 (1995) 167] the theo retical approach of the determination of the critical micelle concentr ation (CMC) by capillary electrophoresis and validated this new techni que with the determination of the CMC of sodium dodecyl sulphate in a simple electrolyte, we demonstrate in this paper the universality of t his technique in studying the evolution of the CMC of the same surfact ant in various complex electrolytic solutions. The electrolytic salts (sodium berate and phosphate) and the solvents (methanol, ethanol, ace tone and acetonitrile) evaluated in this study correspond to the most used salts and solvents in micellar electrokinetic chromatography. Thi s unique possibility offered by this new technique to study the micell e formation under identical electrophoretic conditions as used during the separation appears to be most interesting for the understanding of the separation forces and their optimisation. Moreover, a comparative study of the effect of added organic solvent to the electrolytic medi um has been undertaken.