Micellar electrokinetic chromatography using mixed sodium dodecyl sulfate and sodium cholate

The migration behavior of fifteen dansylated amino acids, two estrogens, and two poly-cyclic aromatic hydrocarbons (PAHs) was studied by micellar electrokinetic chromatography (MEKC) with mixed micelles. The buffer system consisted of 10 mM berate at pH 9.0, containing 50 mM total surfactant concentration. Five different ratios of sodium dodecyl sulfate (SDS) and sodium cholate (SC) surfactants were used, namely. 100:0, 75:25, 50:50, 25:75, and 0:100 (SDS:SC). The numbers refer to molar ratio percent. The migration time window was 50% larger in 50:50 (SDS:SC) compared to 100% SC, and 15% larger than that of 100% SDS. The migration times of PAHs and estrogens exhibited a pattern similar to that of Sudan III in all the SDS/SC mixed micellar systems, due to their hydrophobic property. Although most amino acids are negatively charged at pH 9, their migration patterns were different depending on their R-group. The migration times of amino acids with negatively charged R-groups increased continuously with increasing percent of SC in the SDS/SC mixed micellar systems, while the migration time of amino acids with positively charged R-group continuously decreased with increasing percent of SC in the SDS/SC mixed micellar system. For other groups of amino acids, the migration times in SDS/SC mixed micellar systems exhibited variation without specific pattern. In general, the use of SDS and SC mixed micelles extended the migration time window to some extent, but it was not sufficient to get satisfactory resolution for the amino acids tested in this study.