In this paper we investigate displacement chromatography of amino acids on columns of strong anionic resins in the hydroxyl form. The displacer used here is carbon dioxide dissolved in water, but the theory is also valid to other types pf displacers. A theoretical study of the effect of both dissociation equilibria in solution and ion-exchange equilibria is presented. It is shown that the separation quality depends not only on the selectivity coefficient but also on a term relative to homogeneous equilibria in the liquid phase. This factor is related to the ratio of the second amino acid deprotonation constants.