Separation and determination of lipophilic corticosteroids and benzothiazepin analogues by micellar electrokinetic chromatography using bile salts

Abstract

The separation of corticosteroids and benzothiazepin analogues by micellar electrokinietic chromatography (micellar EKC) was studied in comparison with capillary zone electrophoresis. The separation of these substances was not successful under neutral and alkaline conditions because they migrated with the same velocity as that of the electroosmotic flow. Micellar EKC with sodium dedecyl sulphate ( SDS) solutions was also not successful because these substances migrated with almost the same velocity as that of the SDS micelle, owing to their high liphophilicity. The use of bile salts, which have a similar skeleton to corticosteroids, as the micellar phase permitted the separation of these substances with high theoretical plate numbers (150 000–350 000) within a short time ( ca. 15 min). Sodium cholate was particulary useful. The effects of bile salt concentration, pH and the addition of methanol were investigated. Micellar EKC was also applied to the determination of the drug substances in tablets and cream using the internal standard method and to purity testing of drug substances and tablets.