STRUCTURE-RETENTION RELATIONSHIPS OF DIASTEREOMERIC MIXTURES OF LIPIDIC AMINO-ACID CONJUGATES ON REVERSED-PHASE STATIONARY PHASES

The retention parameters of diastereomeric mixtures of 19 lipidic amin o acid conjugates have been determined on Spherisorb ODS and Supelcosi l LC-ABZ stationary phases by changing the acetonitrile concentration in acetonitrile-0.1% trifluoroacetic acid-water mobile phases. In gene ral, better resolution of the diastereomeric mixtures was obtained on the Supelcosil LC-ABZ stationary phase but in some cases the Spherisor b ODS column showed better separation. The presence of silanol groups improved the separation of the diastereomers in those cases. The log k ' values were plotted against the acetonitrile concentrations. In the case of basic derivatives parabolic relationships could be observed on the Spherisorb ODS stationary phase which contains free silanol group s, while always straight lines were obtained on the Supelcosil LC-ABZ column. The slope and the intercept values were calculated for the str aight lines obtained. The octanol-water partition coefficients (log P) and the dissociation constants (pK(a)) of the compounds were also cal culated and were related to the chromatographic parameters. It was fou nd that the chromatographic parameters obtained on the Spherisorb ODS stationary phase showed slightly better correlations with the calculat ed hydrophobicity and pK(a) parameters than those obtained on the Supe lcosil LC-ABZ column, which shows that different retention mechanism c an be expected on the two stationary phases.