High-performance liquid chromatographic enantioseparation of α-substituted glycine analogs on a quinine-based anion-exchanger chiral stationary phase under variable temperature conditions

The retention of enantiomers of chiral analytes, i.e. α-substituted glycine analogs, on a quinine-based anion-exchanger chiral stationary phase was studied in the temperature range of 5-70 °C and at different mobile phase compositions, using isocratic elution in the reversed-phase mode. By variation of both mobile phase composition and temperature, baseline separations could be achieved for these enantiomers. Separation could be optimized more quickly by adjusting the column temperature rather than the mobile phase composition. The dependence of the natural logarithms of retention and selectivity factors (ln k′ and ln α) on the inverse of temperature, 1/T (van't Hoff plots) was used to determine thermodynamic data on the enantiomers. Calculated thermodynamic constants (Δ(ΔH°), Δ(ΔS°) and Δ(ΔG°)) were applied to promote an understanding of the thermodynamic driving forces for retention in this chromatographic system. The elution sequence of the enantiomers in most cases was determined.