The ion exchange equilibria of amino acids (phenylalanine and tyrosine) on a strong-acid cation exchanger resin (PK220) and on a strong-base anion exchanger resin (PA316) has been investigated. Based on experimental fixed-bed saturations at constant pH, each of the resins was previously screened of a set of three commercial lots with different physical properties. Overall mass balances from the saturation curves enabled to evaluate the linear isotherm constants and its dependence with pH. An equilibrium model that takes into account energetic heterogeneities in ion exchangers was successfully used to correlate binary and multicomponent data. (c) 2005 Elsevier Ltd. All rights reserved.