Trace and selective determination of cobalt(II) in water and salt samples using cathodic adsorptive stripping voltammetry in the presence of Pyrogallol Red

A sensitive and selective procedure is presented for the voltammetric determination of cobalt. The procedure involves an adsorptive accumulation of cobalt Pyrogallol Red (PGR) complex on a stationary mercury drop electrode, followed by cathodic stripping voltammetry measurement of the reduction current of the adsorbed complex at –1.17 V (vs. Ag/AgCl). The optimum conditions for the determination of cobalt include pH 11.0, 35 μM Pyrogallol Red, an accumulation potential of –0.9 V (vs. Ag/AgCl) and scan rate 80 mV s-1. The peak current is proportional to the concentration of cobalt over the concentration range 5.0 to 280 ng mL-1 with a detection limit of 1 ng mL-1 and an accumulation time of 140 s. The method was applied to the determination of cobalt in analytical grade NaCl and water samples.