Simultaneous control of electrostatic micellar partition and electroosmotic flow-rate by anion-dominated partition into zwitterionic micelles

The zeta potentials of zwitterionic micelles and capillary walls have been evaluated with capillary electrophoresis. The zeta potential of the micelles is predominantly determined by the nature of anions, while cations of identical valence have marginal effects; the linear relation has been found between the induced zeta potential and the hydration energy of an anion. The zeta potential of the capillary wall is also varied with anionic natures, and there is a good correlation between micellar and capillary wall zeta potential. This strongly suggests that the zeta potential of capillary walls is determined by the partition of anions into the surfactant layer formed on the capillary wall. Thus, we can simultaneously control both the electroosmotic flow-rate and micellar surface potential (in turn electrostatic interaction between micelles and ionic solutes) by varying the type and concentration of electrolytes. This idea has been applied to the separation of aromatic cationic solutes.