Characterization of the SDS-induced electroosmotic flow in micellar electrokinetic chromatography with cationic polyelectrolyte-coated capillaries

Manipulation of the EOF is essential for achieving optimal separations by MEKC. In this paper, we present an extensive investigation of the effect of common experimental conditions on the EOF observed in a capillary coated with poly(diallyldimethylammonium chloride) (PDADMA) polyelectrolyte under MEKC conditions. It was found that highly reproducible cathodal EOF is achieved approximately at or just below the conditional CMC value of SDS in the electrolytes used. At concentrations of SDS greater than the CMC the EOF is independent of pH. The impact of common organic modifiers (ACN, methanol, urea, beta-CD and nonionic surfactant) on the EOF behavior in both a PDADMA-coated capillary and a bare silica capillary is compared. The suppressing effect of organic modifiers on the EOF is much stronger for coated capillary indicating that these compounds additionally reduce the negative charge density on the capillary surface due to alteration of the surfactant coating.