Enantioseparation of phenothiazines in cyclodextrin-modified micellar electrokinetic chromatography

In this study, enantioseparations of five phenothiazines in cyclodextrin (CD)-modified micellar electrokinetic chromatography (MEKC) were investigated using a citrate buffer containing tetradecyltrimethylammonium bromide (TTAB) as a cationic surfactant at low pH. β-Cyclodextrin (β-CD) and hydroxylpropyl-β-CD (HP-β-CD) were selected as chiral selectors. The results indicate that the separation window is greatly enlarged by β-CD concentration and that the separability and selectivity of phenothiazines are remarkably influenced by the concentrations of both β-CD and TTAB, as well as buffer pH. The interaction of thioridazine with β-CDs is considerably reduced in the presence of TTAB micelles due to competitive complexation of thioridazine with TTAB micelles, which is pH-dependent. As a result, effective enantioseparation of thioridazine is simultaneously achievable with that of trimeprazine and promethazine or ethopropazine in MEKC with addition of either β-CD or HP-β-CD, respectively, to a micellar citrate buffer containing TTAB at pH 3.5. Better enantioresolution of thioridazine in MEKC than in capillary zone electrophoresis can be obtained.