Comparison of solute descriptors for predicting retention of ionic compounds (phenols) in reversed-phase liquid chromatography using the solvation parameter model

Two solute descriptors that account for the ionization of phenols under reversed-phase liquid chromatographic conditions are compared for the prediction of retention of phenols and neutral compounds at different mobile phase pH values using the solvation parameter model. One of the descriptors is the P descriptor (a scaled effective acid dissociation constant, P=(14-pK*)/10), proposed in a previous work. The other descriptor [log (1-D(1-f)] is based on the degree of ionization (D) of the phenol and a retention derived parameter (f) with the value f=10(-1.80) for the chromatographic system studied. Calculation of the P descriptor is straightforward since its value is constant for all mobile phase pH*, but estimation of retention requires a different correlation equation for each mobile phase pH*. Ln contrast, the log [1-D(1-f)] descriptor is pH* dependent, but it allows the same correlation equation to be used for the estimation of retention at any mobile phase pH*. The D derived descriptor can be successfully applied to the estimation of retention of basic and amphiprotic compounds, for which the P descriptor has yet to be applied. (C) 1998 Elsevier Science B.V. All rights reserved.