The adsorption of Naproxen enantiomers on the chiral stationary phase Whelk-O1 under reversed-phase conditions: The effect of buffer composition

The adsorption of the Naproxen enantiomers on the chiral stationary phase (S,S)-Whelk-O1 from methanol–water 80:20 (v/v) solutions modified with the addition of acetic acid or an acetic acid–sodium acetate buffer was studied using elution chromatography. Adsorption was found to be best accounted for by a two-site model assuming different retention mechanisms for the two enantiomers. Under experimental conditions causing a considerable degree of solute dissociation, strong distortion of overloaded band profiles is observed. This phenomenon is explained by the superimposition of the adsorption and the dissociation equilibria. The effect of the buffer composition on the retention is discussed and the results compared with previous ones obtained with the same system. The proposed model explains all the principal features of the adsorption of Naproxen on Whelk-O1 that were found earlier. Moreover this model applies well in a wider range of buffer concentrations, encompassing both the eluents in which solute dissociation is suppressed and those in which dissociation is significant.