CHROMATOGRAPHIC BEHAVIOR OF BASIC AMINO-COMPOUNDS ON SILICA AND ODS-SILICA USING AQUEOUS METHANOL MOBILE PHASES

The effects of the variation of pH, methanol concentration, ionic strength and nature of the ions in aqueous methanol mobile phases on the capacity ratios of amprolium (INN), amylocaine, benzocaine, butacaine (INN) and cocaine using both silica and silica surface-modified by treatment with trichloro(octadecyl)silane (ODS-silica) have been investigated. The differences in retention of the solutes on the two columns are related to the partition coefficients between 2,2,4-trimethylpentane and the mobile phase over the pH range studied. Amprolium, a quaternary ammonium salt, had similar retention characteristics on both silica and ODS-silica when a mobile phase containing 0.05 M ammonium formate was used. The retention mechanisms of the species are complex and involve ion exchange with the proton of a surface silanol site, particularly with amprolium, partition of ion pairs and salting-out effects. Applications of these observations to the analysis of erythromycin (INN) and various toxic diamines are given. © 1978.