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

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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-AAILs) 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 AAILs ligands or free l-Arg-ligand. Parameters of the new TAA-AAILs-based LE-CE system such as the alkane chain length of TAA-AAILs, 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-AAILs as chiral ligands in LE-CE is of great potential for enantioseparation.