Abstract
Quinine carbamate-type weak chiral anion-exchange selectors (SOs) and the respective chiral stationary phases (CSPs) have been used for the direct liquid chromatographic enantiomer separation of a wide range of chiral acids. In the present work, we demonstrate that these CSPs can also be extended to chiral discrimination of a set of neutral polar potential NMDA ( N-methyl- d-aspartic acid) and/or AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) antagonist imidazo-quinazoline-dione derivatives (selectands, SAs) using acetonitrile and methanol containing hydro-organic and buffered mobile phases. The influence of mobile phase composition, column temperature and structure variation of the SAs and SOs on retention and enantioselectivity was systematically investigated to gain insight into the overall chiral recognition mechanism. As was expected for the reversed-phase mode, acetonitrile has a stronger eluotropic effect compared to methanol. Except for two analytes, the acetonitrile containing mobile phases provided baseline resolution ( R S) of the enantiomers with R S values ranging between 1.68 and 2.76. Using methanol as the organic modifier enhanced the enantioselectivity. The enthalpic and entropic terms for the SO–SA association were calculated from the linear van’t Hoff plots. Data reveal that the enantiomer separations are predominantly enthalpically driven.
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