Amino acid chiral ionic liquids combined with hydroxypropyl-β-cyclodextrin for drug enantioseparation by capillary electrophoresis.

Four amino acid chiral ionic liquids were evaluated in dual systems with hydroxypropyl-β-cyclodextrin to investigate the enantioseparation by CE of a group of seven drugs as model compounds (duloxetine, verapamil, terbutaline, econazole, sulconazole, metoprolol, and nadolol). The use of two of these chiral ionic liquids (tetramethylammonium L-Lysine ([TMA][L-Lys]) and tetramethylammonium L-glutamic acid ([TMA][L-Glu])) as modifiers in CE is reported for the first time in this work whereas tetrabutylammonium L-lysine ([TBA][L-Lys]) and tetrabutylammonium L-glutamic acid ([TBA][L-Glu]) were employed previously in CE although very scarcely. The effect of the nature and the concentration of each ionic liquid added to the separation buffer containing the neutral cyclodextrin on the enantiomeric resolution and the migration time obtained for each drug, was investigated. A synergistic effect was observed when combining each chiral ionic liquid with hydroxypropyl-β-cyclodextrin in the case of the five compounds for which the cyclodextrin showed enantiomeric discrimination power when used as sole chiral selector (duloxetine, verapamil, terbutaline, econazole, sulconazole). Buffer concentration and pH, temperature and separation voltage were varied in order to optimize the enantiomeric separation of these five compounds using dual systems giving rise to resolutions ranging from 1.1 to 6.6.