Peculiarities of an imidazole derivative retention mechanism in reversed-phase liquid chromatography: β-cyclodextrin concentration and temperature considerations

Abstract

The retention mechanism of a series of imidazole derivatives in reversed-phase liquid chromatography (RPLC) was investigated over a range of column temperatures and β-cyclodextrin concentrations. The changes in van't Hoff plots as a function of the β-cyclodextrin concentration were examined. Enthalpy, entropy and the Gibbs free energy were determined for the two physicochemical processes: (i) the solute transfer from the mobile to the stationary phases, (ii) the solute complexation by β-cyclodextrin. These thermodynamic data showed that the solute retention mechanism was dependent on the β-cyclodextrin concentration in the mobile phase. Enthalpy–entropy compensation revealed that the main parameter determining retention increased as follow: β-cyclodextrin⇄solute complexation>RP 18 stationary phase⇄solute interaction. This fact confirms that the main parameter determining retention in RPLC is the distribution of the solute molecule in the mobile phase, whereas the interactions with the stationary phase play a minor role.