Abstract: The polarographic catalytic prewaves of metal complexes have been used successfully for determining small quantities of non-electroactive species, an outstanding example for the determination of metals is the AC polarography of Eu-v-phenanthroline. The reaction mechanism of this prewave are examined by many electrochemical experiments such as AC polarography, differential pulse polarography, electrocapillary curves, cyclic voltammetry, etc. A ligand-bridge mechanism is then suggested in comparison with the formation of electroactive complexes in the case of Co ( Ⅱ ) or Ni ( Ⅱ ) with o-phenanthroline.

Key words: Catalytic prewave, Eu( Ⅲ )-o-phenanthroline, Ligand-bridge mechanism