Mixed micellar electrokinetic chromatography of corticosteroids

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Abstract
Mixed micellar electrokinetic chromatography (MMEKC) using mixtures of bile salt surfactants and/or sodium dodecyl sulfate (SDS) was employed to separate a group of corticosteroids. Resolution in electrokinetic chromatography (EKC) can be greatly enhanced by the use of mixed micellar systems due to the fact that the composition of the mixed micelles has a great influence on retention, selectivity and the size of the elution window. By combining surfactants with different structural properties, solute-micelle interactions were manipulated in order to elicit specific separations. Various combinations of bile salts and/or SDS at different mole fractions as well as total micelle concentrations were used in order to enhance the resolution of corticosteroid separations. Large changes in retention and selectivity were observed that often resulted in frequent variations in elution order. In addition, the composition of mixed micellar systems had a great influence on the elution window in EKC, as measured by the ratio of tmc/ teo. Addition of SDS to the mixtures of bile salt micelles resulted in significant extension of the elution window and subsequently improvement in resolution. A separation of seventeen corticosteroids was achieved. Finally, MMEKC was applied in order to separate the steroidal components of a mixture of three anti-inflammatory creams.