Determination of critical micelle concentration of SDS in formamide by capillary electrophoresis

Using an organic solvent and a surfactant, the uncharged, hydrophobicp-arylacetophenones have been separated by micellar electrokinetic chromatography. As an example, the effect of formamide containing sodium n-dodecyl sulfate (SDS) on the separation has been studied. Separations of all selected uncharged hydrophobic compounds were shown to be strongly dependent on the concentration of surfactant. It is suggested that if there is no micelle formed in the formamide solvent, the uncharged hydrophobic compound cannot be separated even though in the presence of surfactant. The electro-migration of solutes was considered zero. After micelle formation, the uncharged compounds were partitioned between the micellar and the organic solvent phases. Neutral molecule partition in and out of micelles depends on the hydrophobicity of each analyte. Based on this suggestion the critical micelle concentrations of SDS, di-(ethylhexyl) sodium sulfosuccinate (AOT) and taurodexycholic acid sodium salt (STDC) in formamide were determined.