Characterization of some functionalized RP-HPLC phases by the use of linear solvation energy relationships

Abstract

The linear solvation energy relationship equation developed by Abraham and coworkers was applied to the retention factors k of a series of 20 polar solutes on four chemically different RP-HPLC phases. Three of them were specially synthesized and are functionalized with ether, phenylsulfide or phenylsulfoxide groups. Their retention properties are compared with those of a nonpolar octadecylsiloxane (ODS) phase. The phase properties r, the excess molar refraction; s, the dipolarity; a and b, the hydrogen-bond basicity and acidity; and v, the cavity factor show significant differences on the four phases and are used here to suggest a classification of stationary phases based on the type of interactions that are important for the retention. The hydrophilic system properties r, s, a and b are the reason for different elution orders of a set of solutes on the four phases. The intrinsic hydrophobicity of the system, the v/A ratio (A is the surface coverage in μmol/m2), shows a dependence on the mobile phase composition as do the normalized phase properties r/v, s/v, a/v and b/v. Averaging the constants over a large span of mobile phase composition should be done very carefully. The LSER model is used to predict the elution order on the stationary phases for five phenols which show coelution on ODS. On the phenylsulfide phase they are resolved.