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

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.