DETERMINATION OF NICKEL AND COBALT IN WASTEWATERS AND SEAWATER BY CONSTANT-CURRENT STRIPPING POTENTIOMETRY WITH NITRITE ENHANCEMENT OF THE STRIPPING SIGNAL

A rapid and highly sensitive method using constant current stripping p otentiometry for the determination of nickel and cobalt in seawaters a nd industrial wastewaters has been established. The method is based on the adsorptive accumulation of nickel and cobalt in the presence of e ither dimethylglyoxime (DMG) or alpha-benzyldioxime (alpha-ED) prior t o stripping using a constant reducing current. Nitrite is used in the stripping step for the catalytic enhancement of the stripping signal. Analytical protocols for standard solutions using DMG or alpha-BD show good precision (RSD's between 3 and 4% on the same film) and detectio n limits (30 ng/L for Ni/DMG; 10ng/L for Co/DMG; 9 ng/L for Co/alpha-B D). However, iron interferes significantly with the determination of c obalt using alpha-BD. With DMG, the simultaneous determination of nick el and cobalt is possible and has been developed into a protocol readi ly applicable to the routine determination of these metals. The analyt ical protocol is rapid, easy to perform and the results are in agreeme nt with those obtained by graphite furnace atomic absorption spectroph otometry. The DMG procedure has also been optimized for the determinat ion of cobalt alone, which has advantages for determinations at concen trations of 1 mu g/L or less.