Abstract: In comparison with the ligand-bridge-mechanism of Eu( Ⅲ )-o-phenanthroline prewave suggested in our previous paper(4), the mechanism of prewaves of Co( Ⅱ ) and Ni( Ⅱ ) with o-phcnan-throline is further investigated by several electrochemical techniques such as ACpolarography, differential pulse polarography, cyclic voltammetry and ultraviolet spectrophotometry, etc. It has been shown that Co( Ⅱ ) and Ni(Ⅱ) form complexes with o-phenanthroline in NH₄Ac solution at pH 7 and 4, respectively. The complexes are adsorbed on the surface of mercury electrode, on which o-pncnan-throline is also adsorbed. The prewaves in the form of sharp, reversible AC polarograms and cyclic voltammograms can be used to determine micro amounts of Co and Ni and also o-phenanthroline. From the results of the experiments it may be concluded that the mechanism of both the Co( Ⅱ ) and Ni( Ⅱ ) prewaves is an electroactive complex mechanism with some differences between them.

Key words: Polarographic catalytic prewave, Co( Ⅱ ) and Ni( Ⅱ ) with o-phenanthroline, Electroac- tive complexes