RETENTION OF RETINOIDS ON AN AROMATIC STATIONARY-PHASE IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

The retention behaviour of retinoids, which are pi-electron containing solutes, on a phenyl stationary phase was studied using mobile phases consisting of aqueous methanol (MeOH; 76-84 % v/v) and acetonitrile ( ACN; 60-82 % v/v) at five temperatures (40-60 degrees C). Retention wa s increasingly affected in both mobile phases by temperature and molec ular structure with increasing water content. The effects of mobile-ph ase composition and especially temperature, on retention were smaller in ACN than in MeOH. With high ACN content the pi-pi interactions tend to decrease retention by increasing the interaction between the solut e molecules and the mobile phase and restricting the adsorption of the solute molecules onto the stationary phase surface. Because the speci fic interactions between solute molecules and the stationary phase are stronger in MeOH and highly aqueous ACN, retention is enhanced. The p i-pi interactions have a significant effect on the selectivity of chro matographic separations when the sample compounds differ in their elec tron donor/acceptor capacities.