Chiral Separations of Cationic and Anionic Drugs on an Alpha 1-acid Glycoprotein-bonded Stationary Phase (EnantioPac). II. Influence of Mobile Phase Additives and PH on Chiral Resolution and Retention

The influence of mobile phase additives and pH on chiral resolution and retention on a high performance liquid chromatographic chiral stationary phase composed of alpha 1-acid glycoprotein bonded to diethylaminoethyl silica (EnantioPac) has been investigated. Cationic and anionic compounds of widely differing structures were chromatographed and drastic effects on stereoselectivity were observed with hydrophobic charged modifiers. For cationic solutes, a decrease in the pH of the mobile phase from 7.0 to 6.0 gave reduced retention and, in some cases, improved selectivity when tetrabutylammonium or tetrapropylammonium bromide was used as modifier. For anionic solutes, a pH decrease from 6.6 to 6.1 gave enhanced retention but without a significant change in stereoselectivity. The steric bulk and hydrophobic moieties of the solute seem to have a strong influence on chiral selectivity. Widely different separating efficiencies were obtained with molecules of different structures.