Catalytic-adsorptive stripping voltammetry of cobalt in the presence of 2,2'-bipyridine and nitrite

A highly sensitive and selective procedure is presented for the voltammetric determination of cobalt. The procedure involves an adsorptive accumulation of cobalt-2,2'-bipyridine complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of nitrite at -1.25 V (vs. Ag/AgCl). The optimum conditions for the analysis of cobalt include 0.1 M ammonium buffer (pH 8.55-9.25), 2.0-5.0 mu M 2,2'-bipyridine, 0.20 M sodium nitrite and an accumulation potential between -0.75 and -0.90 V (vs. Ag/AgCl). An accumulation time of 30 s results in a very low detection limit of 9.5 pM (0.56 p.p.t.) and a linear current-concentration relationship up to 2.0 nM, The relative standard deviation at 0.10 nM is 4.9% Possible interferences from co-existing ions are also investigated.