Equilibrium data for the extraction of alpha-phenylglycine and aspartic acid from dilute aqueous solutions at 30 degrees C, using Amberlite XAD resin impregnated with tri-alkyl-methyl-ammonium chloride (TOMAC), were experimentally studied. The effects of the polymeric support, the amino acid concentration and the pH of aqueous solutions containing individual and binary mixtures of the amino acids were investigated. Amino acid extraction was highest at pH >= 11 using Amberlite XAD-4 impregnated with TOMAC. Equilibrium models, which take account of the simultaneous reactive extraction of the amino acids and the co-extraction of hydroxyl ions by the TOMAC immobilized inside the particle pores, showed good correlation with the experimental data. (c) 2007 Elsevier Ltd. All rights reserved.