Reversed-phase ion-pair chromatography of naphthaleneacetic acid derivatives with water and an organic modifier as the mobile phase

Abstract

The retention behavior of three naphthaleneacetic acid derivatives on two hydrophobic supports, LiChrosorb RP 8 and Spherisorb ODS, has been studied with a mixture of phosphate buffer (pH 7) and methanol or acethonitrile as the mobile phase. The addition of quaternary ammonium compounds to the mobile phase increases the capacity factors, indicating a mixed retention mechanism that includes ion-pair partition. Constants for ion-pair extraction and ion-pair formation in the mobile phase have been derived. By gas chromatographic measurements, it was found that LiChrosorb RP 8 adsorbs about 0.18 ml of methanol per gram after equilibration wiht phosphate buffer (pH 7)-methanol (60:40, v/v) as the mobie phase. The effects of the support and the composition of the mobile phase on efficiencies, asymetry and selectivity factors are discussed.