Facilitated transport and separation of aromatic amino acids through activated composite membranes

Activated composite membranes (ACM) containing bis-(2-ethyl-hexyl) phosphoric acid (DEHPA) have been found to facilitate the transport and separation of aromatic amino acids. The ACM, prepared according to a previously established procedure, were used to experimentally determine their behavior for the transport of phenylalanine (Phe), that was used as target amino acid. A general characterization of the Phe transport through DEHPA-ACM membranes including: the existence of facilitated counter transport, reproducibility and the effect of buffering the feed solution has been performed prior to a systematic study of the influence of some chemical transport parameters. In this concern, the initial Phe concentration, the nature and concentration of the stripping agent and the pH of the feed solution have been optimized (the feed phase was 0.5 mM of Phe in a 2 M NaCl solution at pH 3 and a 2 M HCl solution was used as stripping phase). Also, the influence of the DEHPA concentration in the casting solution used to prepare the membrane is established. It is found that the membrane phase controls the rate transport up to a DEHPA concentration of 1200 mM. Finally, although the affinity of the aromatic amino acids phenylalanine, tryptophan (Trp) and tyrosine (Tyr) for DEHPA is in the order Phe > Trp > Tyr, the selectivity of the DEHPA-ACM was found to be Trp > Phe > Tyr. (C) 2001 Elsevier Science B.V. All rights reserved.