Enantioseparation of phenothiazines in capillary zone electrophoresis using cyclodextrins as chiral selectors

In this study, enantioseparations of five phenothiazines, including promethazine, ethopropazine, trimeprazine, methotrimeprazine, and thioridazine, in cyclodextrin (CD)-modified capillary zone electrophoresis were investigated using a phosphate buffer (40 mM) at pH 3.0. We focussed on the separation of phenothiazines with the use of CDs at low concentrations. Three different CDs, including beta-CD, hydroxypropyl-beta-CD (HP-beta-CD) and gamma-CD, were chosen as chiral selectors. The results indicate that effective enantioseparation of phenothiazines, except for methotrimeprazine, is simultaneously achievable with addition of gamma-CD at a concentration of 2.5-6.0 mM. The enantiomers of ethopropazine and trimeprazine are effectively separated with addition of HP-beta-CD at low concentrations, in the range 0.4-6.0 mM, whereas those of promethazine and trimeprazine are baseline resolved with beta-CD at much lower concentrations (0.02-3.0 mM) than with HP-beta-CD. The results also confirm that the separation window is greatly enlarged at low CD concentrations. Moreover, the drastic variations of the electrophoretic mobility of phenothiazines as a function of CD concentration reveal that phenothiazines interact very strongly with CDs in the order gamma-CD