EFFECT OF THE ORGANIC MODIFIER ON THE RETENTION OF RETINOIDS IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

The retention of retinoids in reversed-phase liquid chromatography was studied using aqueous mobile phases of different composition (methanol 94-86 % and acetonitrile 92-82 %) at five temperatures (40-60-degrees-C). With both organic modifiers the effect of the molecular structure increased as the water content and the polarity of the mobile phase increased. The temperature-dependence increased in the same manner with aqueous methanol mobile phases, but decreased slightly with aqueous acetonitrile mobile phases. The pi-pi interactions between the retinoids and acetonitrile diminish when the water content of the mobile phase is increased, as happens also to the hydrophobic interactions with both organic modifiers. The net effect of these changes depends on the composition of the mobile phase. There was excellent correlation of retention with all polarity parameters studied (phi, P', x(e), x(d), x(n), E(T)N, delta(T), delta(o) and delta(d)), when the calculations were made separately with methanol and acetonitrile. The volume fraction of the organic modifier, phi, was the only parameter describing the retention well in both organic modifiers simultaneously.