Investigation of the synergistic effect with amino acid-derived chiral ionic liquids as additives for enantiomeric separation in capillary electrophoresis

Recently, chiral ionic liquids (ILs) have drawn more and more attention in chiral separation by capillary electrophoresis (CE). In this paper, two chiral ILs based on amino acid derivatives, l-alanine and l-valine tert butyl ester bis (trifluoromethane) sulfonimide, were applied for the first time in CE to evaluate their potential synergistic effects with classical chiral selectors (β-cyclodextrin derivatives) for enantiomeric separation. As observed, improved separation of tested drug enantiomers was obtained with the presence of chiral ILs compared to the conventional β-cyclodextrin derivatives separation system. Parameters such as type and proportion of organic modifier, type and concentration of chiral ILs, concentration of chiral selector, buffer pH and applied voltage were systematically investigated with Me-β-CD/chiral ILs as model system to optimize the novel synergistic system, and the best results were obtained when 15 mM chiral ILs were introduced into the 30 mM sodium citrate/citric acid (20% organic modifier included) buffer solution containing 20 mM Me-β-CD at pH 5.0 with a 20 kV applied voltage for naproxen, pranoprofen and warfarin.