In the Ni(II)-dimethylglyoxime (H2DMG)-NH3-NH4Cl (pH9) system, Ni(II) (HDMG)2 is adsorbed on the Hg electrode surface and a sensitive polarog. catalytic current is exhibited. The characteristics of the catalytic current were investigated by several methods. The experimental evidences showed that a zero-valence "active Ni" is formed during the reduction of Ni(II)(HDMG)2, similar to the "active Co" in the Co(II)-HDMG system, and simultaneously HDMG is catalytically reduced by the "active Ni". However the Ni-HDMG system differs from the Co-HDMG system in several aspects: (1) the difference of the structure between Ni(II)-HDMG and Co(II)-H2DMG complex; (2) Ni(II)(HDMG)2 has stronger adsorbability on the Hg electrode surface than that of Co(II)(HDMG)2, and (3) Ni(0) gives a stripping peak at -0.96 HV, while that of Co(0) is at -0.2 V.

Key words: NICKEL, NICKEL, POLAROGRAPHIC ANALYSIS, OXIME, BUTANEDIONE P, CATALYTIC WAVE