Metal affinity liquid membrane: Facilitated transport of nitrite Original Research Article

The immobilized metal affinity chromatography (IMAC) technique principles applied 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 extraction, or the use of a commercial water insoluble organometallic complex. The characteristics of such a metallic complex to transport anions, being stable enough to avoid the leaching of the metal, are established. Once the metallic complex was prepared, it was used as carrier for anions in the corresponding LM (by the interactions of the anions with this specific metal properly immobilised). Pd(II) metal complexes in organic diluent have been studied for the transport of NO2− as specific target system for LM. For this purpose, different types of reagents were used as Pd(II) extractants to get the proper immobilisation of this metal and thus, to accomplish for the best 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 trans-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 contribute to NO2− transport, including the nature of stripping solutions, pH of feed solution and membrane modifiers. Selectivity of the liquid membrane transport has been also determined as well as the influence of membrane modifiers in the selectivity of anion transport. The results have been compared to the behaviour of the BPP–Pd(II) complex as ISE carrier for anions.