Determination of critical micelle concentration values using capillary electrophoresis instrumentation

The purpose of this work is to demonstrate the usefulness of capillary electrophoresis (CE) instrumentation for determining values of critical micelle concentration (cmc) of surfactants, The approach essentially consists of a CE version of the traditional method of measuring values of cmc by conductivity. Namely, the different conductivities of ionic surfactants in solution depending on their aggregation state, i.e., as monomers or micelles, and the effect on the electrical current as usually measured in a CE apparatus are employed to determine the cme values. The cmc of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) is obtained in several media such as water, aqueous solutions containing salts, organosaline solutions, and aqueous Solutions containing beta-cyclodextrin. The cmc values for SDS and CTAB under these conditions are in good agreement with those reported in the literature. Advantages and drawbacks of this procedure as well as its implications in micellar electrokinetic chromatography are discussed. From our results, it is deduced that the present method can be used with high confidence to determine values of cmc in a fast and easy way.