Highly copper(II) ion-selective transport through liquid membrane containing 1-(2-pyridylazo)-2-naphthol.

often an important process in industry and chemical analysis. Liquid-membrane transport in which the extraction and stripping operations are combined in a single process reduces the solvent inventory requirement, and also allows the use of expensive and highly selective extractions, which otherwise would be uneconomic in solvent extractants. For these reasons, liquid-membrane transport has attracted worldwide attention, and much work has been directed toward developing methods for its application to the separation of various metal ions. 1–12 Proton-driven cation transport through a liquid membrane containing an ion-selective ionophore bearing a proton-dissociable moiety is one of the most effective separation techniques for a particular metal ion. 13–16 In this membrane cation transport system, there is no need for the counter anion to counterbalance the positive charge, because the proton-dissociated ionophore, itself, acts as the counter anion of the complexing cation. Therefore, the cation transport ability is independent of the extent of hydrogen of a counter anion. Uphill transport against a cation concentration gradient is also feasible, since cations are transferred by the counter transport of protons. Different methods for the specific transport of Cu(II) ions across a liquid membrane have been reported which have drawbacks of a slow rate for transport or a lack of high selectivity. 17–22 For example, it has been reported that N,N′-bis(8-quinolyl)glutaramide can selectivily and effectively transport copper ion (63%) through a choloroform membrane after 2 days. 20 Therefore, the development of effective and specific systems for studying the transport of metal ions, particularly Cu(II), is a remarkable task from both practical and theoretical viewpoints. 1-(2-Pyridylazo)-2-naphthol (PAN) is a dye, which tends to form a complex with some metal ions. It is used as a photometric reagent (with or without extraction) for a wide variety of metal ions and as a metal indicator in chelatometric titration. To the best of our knowledge, no work on the use of PAN as a carrier in transport systems has been reported previously. In this paper we report that PAN is an excellent carrier for the high selectivity, rapid and uphill transport of Cu(II) ions through a liquid membrane. Experimental Reagents PAN was purchased from Merck chemical company and used as received. Reagent-grade chloroform (Fluka) was used as a membrane organic solvent. A stock solution of copper (1.26 × 10 –2 mol/L) was prepared by dissolving an appropriate amount of Cu(NO3)2·3H2O (Fluka) in a 1000 mL calibrated flask and diluting to …