ELECTROKINETIC CHROMATOGRAPHY USING THERMODYNAMICALLY STABLE VESICLESAND MIXED MICELLES FORMED FROM OPPOSITELY CHARGED SURFACTANTS

The electrokinetic chromatography (EKC) of a novel mixed surfactant sy stem consisting of oppositely charged surfactants, sodium dodecyl sulf ate (SDS) and n-dodecyltrimethylammonium bromide (DTAB), was investiga ted. The chromatographic characteristics of large liposome-like sponta neous vesicles and rodlike mixed micelles formed from the mixture were explored and compared with those of SDS micelles. Separations of a se ries of 12-alkylphenones showed that the spontaneous vesicles provided about a 2 times wider elution window than SDS micelles. Both vesicle and mixed micelle systems were found to provide larger methylene selec tivity than SDS. The different elution order of a group of nitrotoluen e geometric isomers with DTAB/SDS spontaneous vesicles and SDS micelle s pseudostationary phases suggested the possibility of different separ ation mechanisms with these two systems. Comparisons of polar group se lectivity, retention, and efficiency were made between vesicles, mixed micelles, and SDS micelles. The correlation between the logarithms of the retention factors (log k') and octanol-water partition coefficien ts (log P-ow) for a group of 20 neutral compounds was also studied wit h DTAB/SDS vesicles. Spontaneous vesicles have great potential as a ps eudostationary phase in electrokinetic chromatography.