An interaction between Ni
2+ and purine derivatives, such as adenine, 6-chloropurine, 6-hydroxypurine, 6-methylpurine, 6-mercaptopurine and purine, at a mercury electrode-electrolyte interface was investigated. In the presence of purine derivatives, a catalytic prewave of Ni
2+ prior to their reduction waves was observed on a direct current (DC) polarogram. The prewave was affected by the concentrations of Ni
2+ and purine derivatives. Addition of gelatin caused the disappearance of the prewave, suggesting that the electrode process of the prewave involves the adsorption of purine derivatives and/or their complexes with Ni
2+ on the electrode surface. Effects of concentration and nature of cation of supporting electrolyte (nitrates were used) were also examined : The prewave height (i
pre) was markedly lowered with increasing concentration and i
pre was given in the order of Li
+>Na
+>Cs
+. On the basis of the experimental results, a possible reaction mechanism was proposed taking the following facts into consideration : Ni (H
2O)
62+ is transported to the electrode surface through diffusion, then the complex formation takes place immediately between Ni
2+ and preadsorbed purine derivatives, and the resulting complexes are more easily reduced than Ni (H
2O)
62+.
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