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

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 + rR(2) + s pi(2)(H) + a Sigma alpha(2)(H) + b Sigma beta(2)(H) nu V-x. The solute descriptors are the excess molar refractivity, R-2, the dipolari ty/polarizabiIity, pi(2)(H), the overall hydrogen bond acidity, Sigma alpha (2)(H), the overall hydrogen bond basicity, Sigma beta(2)(H), and the McGow an volume, V-x. The obtained correlations are significantly worse than thos e of reversed phase liquid chromatography (RPLC). However, they show that, in contrast with the reversed-phase chromatographic behavior, solute dipola rity/polarizability and hydrogen bonding abilities increase the retention. In bonded-phase columns (amino, dimethylamino and diol) the refractivity te rm shows a moderate statistical significance and it contributes to the elut ion process, whereas the volume does not; however, in silica columns the so lute volume becomes a relevant property. (C) 1999 Elsevier Science B.V. All rights reserved.