Metal affinity liquid membrane - II. Facilitated transport of tryptophan

A new supported liquid membrane system based on a palladium carrier (trans- benzylchloride bis-triphenylfosfine palladium(II) (BPP-Pd (II))) for the tr ansport and pre-concentration of amino acids has been characterised. The am ino acid tryptophan (Trp) has been used as a target for the membrane transp ort. The affinity of the anionic form of Trp for the metallic centre (Pd(II )) is the power that maintains the extraction of the amino acids. The lower pH in the receiving phase changes the speciation of the amino acid leading to its release in the receiving phase. Various parameters that characteris e the Trp transport by this liquid membrane have been studied, i.e. carrier concentration, stripping agent, concentration of the stripping agent, pH i n the donor phase and pre-concentration time. A valuable pre-concentration factor of 45 was achieved with an initial Trp concentration of 0.1 mM at pH 9 of the donor solution and after 40 h of running the transport experiment . (C) 2000 Elsevier Science B.V. All rights reserved.