Voltammetric Study of the Transfer of Heavy Metal Ions at Nitrobenzene/Water Interface Assisted by 1,4,7,10,13,16-Hexathiacyclooctadecane

The transfer of Cd2+, Pb2+, Hg2+, Pd2+, and Cu2+ ions across polarized nitrobenzene/water (NB/W) interface assisted by 1,4,7,10,13,16-hexathiacyclooctadecane (HTCO) present in NB-phase has been studied by means of cyclic voltammetry. Voltammograms of Cd2+ and Pb2+ ions can be interpreted as being due to the reversible transfer of the ions assisted by the formation of 1:1 metal(M)-HTCO complex in NB-phase. The formal formation constants of [PbHTCO]2+ and [CdHTCO]2+ complexes in NB-phase have been determined to be 1011.7±0.3 and 107.9±0.3 M-1, respectively, using the formal potentials of non-assisted ion(M)-transfer at NB/W interface (ΔWNB φ0′M). The ΔWNB φ0′M’s of Cd2+ and Pb2+ ions and Zn2+ and Tl+ ions as well have been determined on the basis of the tetraphenylarsonium-tetraphenylborate assumption and of the polarographic reversible half-wave potentials of the ions in NB- and W-media reported by previous authors. Voltammograms of Hg2+ and Pd2+ ions have been explained by that 1:1 M-HTCO complex is formed and soluble in both NB- and W-phases. The formal potentials of the transfer of [HgHTCO]2+ and [PdHTCO]2+ complex ions at NB/W interface have been determined. Voltammograms of Cu2+ ion are of irreversible nature.