Optimized separation of seven corticosteroids by micellar electrokinetic chromatography

The corticosteroids studied can be effectively separated by employing micellar electrokinetic capillary chromatography (MECC). The effect of pH, borate concentration and the sodium dodecyl sulfate (SDS) concentration on both the resolution and the selectivity was studied under 15 different experimental conditions. The experimental design was similar to the central composite design approach. Empirical quadratic regression models were derived for analyte migration time, band broadening and analyte velocity. Satisfactory regression fits and coefficients of determination for prediction were obtained with cross-validated models. The models for analyte migration time and analyte velocity were in good agreement with theory. Modeling of the band broadening seemed to be somewhat more complicated. Optimum conditions for resolution and selectivity were different. This is due to the fact that selectivity studies ignore the electroosmotic and band broadening properties of different electrolyte solutions. However, the study of the selectivity yielded good information about the suitability of the electrolyte systems for the particular separation problem. Although a high solubilizing power of SDS caused the corticosteroids to partition strongly into the SDS micelles, a good separation could be achieved at low SDS concentrations.