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

The linear solvation energy relationship equation log k = c + rR(2) + s pi(2)(H) + a Sigma alpha(2)(H) + b Sigma beta(2)(H) vV(x)/100 developed by Abraham and coworkers was applied to the retention factors k o f 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 c ompared with those of a nonpolar octadecylsiloxane (ODS) phase. The phase p roperties r, the excess molar refraction; s, the dipolarity; a and b, the h ydrogen-bond basicity and acidity; and v, the cavity factor show significan t differences on the four phases and are used here to suggest a classificat ion of stationary phases based on the type of interactions that are importa nt for the retention. The hydrophilic system properties r, s, a and b are t he reason for different elution orders of a set of solutes on the four phas es. The intrinsic hydrophobicity of the system, the v/A ratio (A is the sur face coverage in mu mol/m(2)), shows a dependence on the mobile phase compo sition as do the normalized phase properties r/v, s/v, a/v and b/v. Averagi ng the constants over a large span of mobile phase composition should be do ne very carefully. The LSER model is used to predict the elution order on t he stationary phases for five phenols which show coelution on ODS. On the p henylsulfide phase they are resolved.