Metal affinity liquid membrane - Facilitated transport of nitrite

The immobilized metal affinity chromatography (IMAC) technique principles a pplied to the facilitated transport of anions across liquid membranes (LM) is shown. Two approaches have been developed for preparing the LM carrier: either the formation of a metallic complex, by the appropriate metal extrac tion, or the use of a commercial water insoluble organometallic complex. Th e characteristics of such a metallic complex to transport anions, being sta ble enough to avoid the leaching of the metal, are established. Once the me tallic complex was prepared, it was used as carrier for anions in the corre sponding LM (by the interactions of the anions with this specific metal pro perly immobilised). Pd(II) metal complexes in organic diluent have been stu died for the transport of NO2- as specific target system for LM. For this p urpose, different types of reagents were used as Pd(II) extractants to get the proper immobilisation of this metal and thus, to accomplish for the bes t transport of NO2-. Among them, tri-isobutylfosfine sulphide (Cyanex 471) was found to provide best characteristics as anion carrier for the organic Pd(II)-Cyanex 471 complex. On the other hand, the organometallic complex tr ans-benzylchloride bis-triphenylfosfine palladium(II) (BPP-Pd(II)) has been studied as nitrite carrier, providing a higher rate of transport than the Pd(II) extracted complex. Different parameters have been investigated to co ntribute to NO2- transport, including the nature of stripping solutions, pH of feed solution and membrane modifiers. Selectivity of the liquid membran e transport has been also determined as well as the influence of membrane m odifiers in the selectivity of anion transport. The results have been compa red to the behaviour of the BPP-Pd(II) complex as ISE carrier for anions. ( C) 2000 Elsevier Science B.V. All rights reserved.