Evaluation of tetraalkylammonium amino acid ionic liquids as chiral ligands in ligand-exchange capillary electrophoresis

The application of chiral ionic liquids (ILs) in capillary electrophoresis (CE) for enantioseparation has received considerable attention in the past few years; however, the use of chiral ILs as ligands in ligand-exchange capillary electrophoresis (LE-CE) has been reported only in a few papers. In this work, several tetraalkylammonium amino acid ILs (TAA-AAlL5) including tetramethylammonium-L-arginine (TMA-L-Arg), tetramethylammonium-L-proline (TMA-L-Pro) and tetramethylammonium-L-glutamic acid (TMA-L-Glu) were first applied in LE-CE to act as chiral ligands for enantioseparation. The results show that TMA-L-Arg-is an excellent chiral ligand, and able to yield equal or even better resolutions (Rs) in much shorter migration times for most tested analytes compared with previously reported AAlLs ligands or free L-Arg-ligand. Parameters of the new TAA-AAlLs-based LE-CE system such as the alkane chain length of TAA-AAlLs, ILs configuration, ILs concentration, the type and concentration of central metal ion, buffer pH and applied voltage were optimized. Satisfactory enantioseparations were achieved for most selected free- or dansyl-amino acids. The method was then successfully applied to the enantiomeric impurity test of a commercial amino acid sample. This work indicates that the application of TAA-AAlLs as chiral ligands in LE-CE is of great potential for enantioseparation. (C) 2019 Elsevier B.V. All rights reserved.