Effects of Physical Parameters onto Adsorption of the Borderline Amino Acids Glycine, Lysine, Taurine, and Tryptophan upon Amberlite XAD16 Resin

The adsorption of the borderline amino acids glycine, lysine, taurine, and tryptophan on the commercial resin Amberlite XAD16 was investigated. The effect of amino acid hydrophobicity/hydrophilicity and effects of environmental conditions upon adsorption equilibrium were evaluated. Optimal settings for a maximum recovery of a selected amino acid, namely, taurine, were obtained by the response surface methodology. Changes in temperature, pH, ionic strength, percentage of ethanol added to the amino acid solution, amino acid concentration, and adsorbent dose showed effects on the recovery of each amino acid upon the uncharged, nonfunctionalized, and hydrophobic matrix of the Amberlite XAD16 resin. Adsorption was favored at the lower temperature investigated, 10 degrees C; a pH decrease down to 2 favored adsorption of glycine, lysine, and tryptophan; the addition of ethanol allowed an increase in amino acid recovery except for lysine. The addition of sodium chloride up to the value of 1.5 M showed a positive effect on adsorption of all amino acids. A dose of 10 g Amberlite XAD16 for 100 mL of solution was the most adequate at the amino acid concentrations tested. Optimal conditions for the maximum recovery of taurine were achieved at a temperature of 13.5 degrees C and at a ionic strength of 1.32 M NaCl.