MICELLAR ELECTROKINETIC CHROMATOGRAPHY USING MIXED SODIUM DODECYL-SULFATE AND SODIUM CHOLATE

The migration behavior of fifteen dansylated amino acids, two estrogen s, and two poly-cyclic aromatic hydrocarbons (PAHs) was studied by mic ellar electrokinetic chromatography (MEKC) with mixed micelles. The bu ffer system consisted of 10 mM berate at pH 9.0, containing 50 mM tota l surfactant concentration. Five different ratios of sodium dodecyl su lfate (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 mola r ratio percent. The migration time window was 50% larger in 50:50 (SD S:SC) compared to 100% SC, and 15% larger than that of 100% SDS.The mi gration times of PAHs and estrogens exhibited a pattern similar to tha t 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-g roups increased continuously with increasing percent of SC in the SDS/ SC mixed micellar systems, while the migration time of amino acids wit h positively charged R-group continuously decreased with increasing pe rcent of SC in the SDS/SC mixed micellar system. For other groups of a mino acids, the migration times in SDS/SC mixed micellar systems exhib ited variation without specific pattern. In general, the use of SDS an d SC mixed micelles extended the migration time window to some extent, but it was not sufficient to get satisfactory resolution for the amin o acids tested in this study.