Displacement chromatography of amino acids: Effects of selectivity reversal

Publisher Website
Google Scholar
Abstract
Separating mixtures of α‐amino butyric acid (ABA) and isoleucine (Ile) by displacement chromatography with a cation exchange resin and an alkaline displacer leads to the formation of a displacement train, in which only ABA is recovered as a pure component, while Ile is recovered in a mixed band with ABA. The purity of the Ile band depends on the concentration of the displacer, and essentially pure Ile is obtained when the displacer concentration is reduced to a low value. The observed behavior is explained by considering the nonideality of the equilibrium uptake of these amino acids by the resin. An equilibrium model, representing the pure component isotherms, predicts variable selectivity and the occurrence of selectivity reversal in the two‐component system. Analyses using this model based on the theory of coherent waves and a numerical solution of the conservation equations for the displacement chromatography process agree with the observed behavior, predicting the formation of “azeotropic” bands during the development of the displacement train. Such analyses are used to determine under what conditions a complete separation may be obtained for a given experimental system.