Analytical Sciences

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

Hajime KATANO and Mitsugi SENDA

Department of Bioscience, Fukui Prefectural University, Matsuoka-cho, Fukui 910-1195, Japan

The transfer of Cd 2+ , Pb 2+ , Hg 2+ , Pd 2+ , and Cu 2+ 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 Cd 2+ and Pb 2+ 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 10 11.7±°.3 and 10 7.9±°.3 M -1 , respectively, using the formal potentials of non-assisted ion(M)-transfer at NB/W interface ( D W NB fM 0¡þ). The D W NB fM 0¡þÕó of Cd 2+ and Pb 2+ ions and Zn 2+ and Tl + ions as well have been determined on the basis of the tetraphenylarsonium-tetraphenylborate assumption and of thepolarographic reversible half-wave potentials of the ions in NB- and W-media reported by previous authors. Voltammograms of Hg 2+ and Pd 2+ 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 inter-face have been determined. Voltammograms of Cu 2+ ion are of irreversible nature. (Keywords: Voltammetry, polythiaether, assisted transfer, heavy metal ion, polarizable oil/water interface)

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