Comparison of the influence of organic modifier on the secondary interactions of polar embedded and classical alkyl-silica reversed phase HPLC stationary phases.

Linear solvation energy relationships are used along with solute retention data to compare the influence of organic modifier on the secondary interactions of polar-embedded (EPG) and classical alkyl-silica (C18) stationary phases. System constants derived using the linear solvation energy relationship model measure the relative strength of solute interactions in the mobile phase and the solvated stationary phase. Differences in the e and s system constants, which, respectively, measure interactions of pi and lone pair electrons and dipole-type interactions, were larger between the two stationary phases when methanol was used versus ACN. A similar effect was not evident for the a system constant, which is a measure of hydrogen-bond acceptor ability. The b system constant, which measures hydrogen-bond donating ability, was consistently lower for the EPG stationary phases when water-methanol mobile phases were used, especially at lower methanol levels. Plots of the polar and specific selectivity for select solutes versus organic modifier level are used to demonstrate the differing influences of ACN and methanol on the selectivity obtained on representative EPG and C18 stationary phases. For the solutes studied, differences in both the polar and specific selectivity were increased between the two stationary phases when water-methanol mobile phases were used.