Effect of Mobile-Phase Composition on Pressure-Induced Shifts in Solute Retention for LC Separations using b-Cyclodextrin Stationary Phases

Ž . Abstract: Modest pressure 350 bars has a significant impact on reversed-phase liquid chromatographic retention using b-cyclodextrin stationary phase. Demonstrated here for separations of the positional isomers of nitrophenol and naphthol as well as the enantiomers of hexobarbital and mephobarbital, the effect of small pressure perturbations on solute capacity factor ranges from q11 to y14%. These changes in retention arise from pressure-induced shifts in solute equilibria and are used to estimate the change in molar volume upon solute binding with b-cycloŽ . dextrin DV . In this article, the effect of the mobile phase on pressure-induced comp shifts in solute retention is examined. Mobile-phase composition is observed to have a significant influence on the change in solute capacity factor with pressure and therefore on DV . As the composition of water in the mobile phase comp increases, the change in partial molar volume of complexation is observed to become more positive for both positional isomer and chiral separations. Although these studies imply that changes in solvent composition have a general effect on the observed DV and therefore on the change in pressure perturbation with comp solvent composition, it is clear that more studies are needed to establish the exact nature and breadth of this effect. Q 1998 John Wiley & Sons, Inc. J Micro Sep 10: 647]652,