ELECTROCHEMICAL AND SPECTROSCOPIC INVESTIGATION OF THE REDUCTION OF DIMETHYLGLYOXIME AT MERCURY-ELECTRODES IN THE PRESENCE OF COBALT AND NICKEL

Voltammograms (polarograms) obtained from solutions of cobalt and nick el containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals, Detailed electrochemical and spectrosc opic studies on the reduction process observed in the analytically imp ortant ammonia buffer media at mercury dropping, hanging, and pool ele ctrodes are all consistent with an overall 10-electron reduction proce ss, in which both the dmgH(2) ligand and cobalt ions are reduced in th e adsorbed state: Co(II) + 2dmgH(2) reversible arrow (solution) [Co-II (dmgH)(2)] + 2H(+); [Co-II(dmgH)(2)] + Hg reversible arrow (electrode) [Co-II(dmgH)(2)](ads)-Hg; and [Co-II(dmgH)(2)](ads)Hg + 10e(-) + 10H( +) --> Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubilit y of the nickel complex in aqueous media restricts the range of studie s that can be undertaken with this system, but an analogous mechanism is believed to occur, Low-temperature voltammetric studies in dichloro methane at a frozen hanging mercury drop electrode and in situ electro n spin resonance electrochemical measurements on more soluble analogue s of the dimethylglyoxime complexes are consistent with an initial one -electron reduction step being available in the absence of water, Deli berate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examin ed, The results of the present study are compared with the wide range of mechanisms proposed in other studies.