Removal of amino acids from water by adsorption on polystyrene resins

The adsorption of eight amino acids, L-asparagine, D,L-threonine, L-lysine, L-leucine D,L-methionine, L-tyrosine, L-phenylalanine and D,L-tryptophan, on the non-polar macroporous adsorbents Amberlite XAD-2 and XAD-4 (polystyr ene-divinylbenzene copolymers) was studied. Equilibrium adsorption experime nts were conducted to estimate the types of isotherm and their parameters. The effect the chemical composition and structure of the amino acids on the efficiency of adsorption was evaluated. The influence of pH and ionic stre ngth was also studied. The data of adsorption isotherms of the examined ami no acids seemed generally to approach the Freundlich isotherm model. Trypto phan isotherm adsorption data could match in some cases the Langmuir model. The majority of the adsorption isotherms were almost linear. In terms of a dsorbed amino acid on both resin surfaces, the amino acids can be ranked th us: D,L-tryptophan > L-phenylalanine > D,L-methionine, L-tyrosine > L-leuci ne > L-lysine > D,L-threonine > L-asparagine. In low pH solution, adsorptio n was generally higher than that at intermediate and high pH values. Genera lly, as the ionic strength increases, the adsorption of the amino acids inc reases. (C) 2001 Society of Chemical Industry.