Determination of the critical micelle concentration of cationic surfactants by capillary electrophoresis

The determination of the critical micelle concentration (CMC) of cationic s urfactants by capillary electrophoresis was demonstrated, In this study, te tradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromi de (DoTAB) were selected as cationic surfactants and propazine was chosen a s test solute. In the evolution of the effective electrophoretic mobility o f propazine as a function of surfactant concentration, a dramatic change in slope at a particular concentration is a good indication of the CMC of thi s surfactant, The CMC values determined experimentally were further confirm ed by a curve-fitting approach. Simulation of the electrophoretic mobility curves as a function of surfactant concentration in both micellar electroki netic chromatography and capillary zone electrophoresis using cationic surf actants as an electrolyte modifier was performed for propazine, and the int ersection of these two mobility curves allowed us to precisely predict the CMC of the surfactant, The CMC values determined for TTAB and DoTAB are 1.6 +/- 0.1 and 11.0 +/- 0.1 mM, respectively, in the case of an electrolytic solution consisting of 70 mM phosphate buffer at pH 6.0, Moreover, the appl icability of the electroosmotic mobility as a parameter for the determinati on of the CMC was examined.