Capillary isotachophoresis as a promising technique for the study of ionic surfactant micellization

Abstract Capillary isotachophoresis was investigated as a complementary technique to the determination of the major electrochemical parameters of ionic micelles, including critical micellar concentration, charge ratio, electrophoretic mobility and parameters of the micellization equation. The leading electrolyte parameters (mainly leading ion concentration, solvent composition and counterion nature) can readily be selected so as to promote and control micellization of the surfactant to be studied in the migration conditions. Then, the determination of the step height and length of the micelle zone give a direct access to micelle mobility and charge ratio. In addition, it was found that, when a given amount of surfactant is injected together with a ca . 2–4-fold amount of a reference mobility marker with a mobility in between those of the free and micellized forms of the surfactant, the micelle zone length is markedly decreased, while that of the marker is increased. This phenomenon was described as a pollution of the marker zone by the free and micellized forms of surfactant, and theoretically interpreted. The straightforward experimental measurement of the level of this pollution provides an additional relationship between most of the micelle parameters.