MIXED MICELLES OF SODIUM DODECYL-SULFATE AND SODIUM CHOLATE - MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY AND NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Physicochemical properties of a mixed micellar system of sodium dodecy l sulfate (SDS) and sodium cholate (SC) were investigated. The micelle -micelle and micelle-buffer interactions in an hyl-2-hydroxyethyl)amin o]-2-hydroxypropanesulfonic acid buffer system for separations by mice llar electrokinetic capillary chromatography (MEKC) were studied by ca pillary electrophoresis (CE) and nuclear magnetic resonance (NMR) tech niques. A mixed micellar system of SDS and SC can effectively be used for the separation by MEKC of highly hydrophobic compounds like cortic osteroids. Marked differences in distribution coefficients of the cort icosteroids were observed when the micellar phase was changed from the highly hydrophobic SDS to the less hydrophobic SC. Measurements of cr itical micelle concentration were made by CE and conductometric titrat ion. The mixed micellar system was further characterized by NMR method s. NMR-based self-diffusion measurements and NMR relaxation measuremen ts showed that SC affects the micellization of SDS primarily by decrea sing the amount of nonmicellized (monomeric) SDS in the mixed system.