Mixed Micelles of Sodium Dodecyl Sulfate and Sodium Cholate: Micellar Electrokinetic Capillary Chromatography and Nuclear Magnetic Resonance Spectroscopy
Physicochemical properties of a mixed micellar systemof sodium dodecyl sulfate (SDS) and sodium cholate (SC)were investigated. The micelle-micelle andmicelle-buffer interactions in an SDS/SC/[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acidbuffersystem for separations by micellar electrokineticcapillarychromatography (MEKC) were studied by capillary electrophoresis (CE) and nuclear magnetic resonance (NMR)techniques. A mixed micellar system of SDS and SC caneffectively be used for the separation by MEKC of highlyhydrophobic compounds like corticosteroids. Markeddifferences in distribution coefficients of thecorticosteroids were observed when the micellar phase was changedfrom the highly hydrophobic SDS to the less hydrophobicSC. Measurements of critical micelle concentrationweremade by CE and conductometric titration. The mixedmicellar system was further characterized by NMR methods. NMR-based self-diffusion measurements and NMRrelaxation measurements showed that SC affects themicellization of SDS primarily by decreasing the amountof nonmicellized (monomeric) SDS in the mixed system.