Influence of mobile phase composition on thermodynamic properties in high-performance liquid chromatography

Tris(1,3-dimethyphenylcarbamate)-derivatized cellulose, bonded to silica, w as used as a chiral stationary phase for the high performance liquid chroma tographic separation of optically active potential drug substance and corre sponding enantiomer over the temperature range of 12 to 40 in the reversed- phase mode. A decrease in temperature caused an increase in the retention f or solutes. The van't Hoff plots generated using acetonitrile/acetate buffe r mobile phase system were nicely linear, thus, we calculated enthalpies an d entropies of solute transfer from the mobile to stationary phase. The inf luence of the mobile phase composition was studied in detail. The cavity fo rmation effect was the major factor that governs the solute distribution be tween the mobile and stationary phases for acetonitrile-rich mobile phase, while the effect of solvation due to acid-base equilibrium became significa nt in highly aqueous mobile phase. Thermodynamic data also revealed that en antio-separation was enthalpy-controlled separation on a chiral cellulose-d erivatized column under iso-enantioselective temperature.