Solute–solvent interactions in normal-phase liquid chromatography: a linear free-energy relationships study Original Research Article

The retention factors, k, of several different series of compounds obtained in a variety of normal-phase liquid chromatographic (LC) systems have been fitted to the following linear free-energy equation:log k=c+rR2+sπH2+aΣαH2+bΣβH2+vVxThe solute descriptors are the excess molar refractivity, R2, the dipolarity/polarizability, πH2, the overall hydrogen bond acidity, ΣαH2, the overall hydrogen bond basicity, ΣβH2, and the McGowan volume, Vx. The obtained correlations are significantly worse than those of reversed phase liquid chromatography (RPLC). However, they show that, in contrast with the reversed-phase chromatographic behavior, solute dipolarity/polarizability and hydrogen bonding abilities increase the retention. In bonded-phase columns (amino, dimethylamino and diol) the refractivity term shows a moderate statistical significance and it contributes to the elution process, whereas the volume does not; however, in silica columns the solute volume becomes a relevant property.