Voltammetric study of the transfer of heavy metal ions at the nitrobenzene | water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine

The transfer of heavy metal ions across the polarized nitrobenzene | water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (DPT) present in the nitrobenzene phase has been studied by normal pulse voltammetry and cyclic voltammetry. Voltammetric waves of Pb2+ and Cd2+ ions were reversible, whereas that of Zn2+ ion was quasi-reversible. Voltammetric waves of Hg2+, Fe2+, and Co2+ ions were more or less irreversible. The voltammogram of Cu2+ ion showed a two-step wave. The dependence of the reversible half-wave potentials of Pb2+, Cd2+, and Zn2+ ions on the concentration of DPT in the nitrobenzene phase reveals that their ion-transfer is assisted by the formation of 1:n metal–DPT complex(es) in nitrobenzene; Pb2+: n=3 and 4 with the formal formation constants (log βnO) of log β3O=18.2±0.1 and log β4O=20.4±0.1; Cd2+: n=3 with log β3O=27.1±0.1; and Zn2+: n=3 with log β3O=36.0±0.1, respectively.