Polar interactions in solid-phase extraction of basic drugs by octadecylsilanized silica.

Polar interactions between basic drugs (pentacaine, propranolol, and stobadin) and C18 silanized silica are studied along with hydrophobic interactions by using elution profiles of the drugs obtained with six organic solvents. The elution ability of the liquids towards basic drugs depends positively on their proton acceptor properties and negatively on their dipole interaction properties. Addition of triethylamine, a strong proton acceptor, to the liquids improves their elution ability, resulting in practically total recovery in all instances. The shapes of elution profiles indicate the presence of multiple types of interactions between C18 silica sorbent and basic drugs, ranging from those that originate from hydrophobic interactions to those originating from solute-sorbent ionic forces.