Conjoint prediction of the retention of neutral and ionic compounds (phenols) in reversed-phase liquid chromatography using the solvation parameter model

The solvation parameter model can be modified to predict the retention of ionized compounds (phenols) under reversed-phase liquid chromatographic conditions by the addition of a further solute descriptor derived from the acid dissociation constant. Two solute descriptors are evaluated for this purpose. The degree of dissociation, D solute descriptor, is defined by Eq. (3), and the scaled effective acid dissociation constant, the P solute descriptor, by (14-pK*)/10. The P solute descriptor provided better predictive accuracy than the D solute descriptor and enabled the retention factor of phenols (log k) to be estimated to 0.1 to 0.2 log units depending on the pH* of the mobile phase. The P solute descriptor is also suitable for use in the conjoint analysis of neutral and ionized compounds with similar predictive accuracy. A significant fraction of the error in retention prediction is due to changes in the solute dipolarity/polarizability pi(2)(H) and effective hydrogen-bond acidity Sigma alpha(2)(H) accompanying ionization that are not allowed for in the current model. (C) 1998 Elsevier Science B.V.