Selective determination of trace cobalt in zinc electrolytes by second-derivative catalytic polarography

Abstract

We report herein a highly selective method for directly determining the trace Co2+ in highly concentrated zinc electrolyte. This novel method is based on a second derivative wave of catalytic adsorptive polarography generated by complexing Co2+ with dimethylglyoxime and nitrite onto a dropping mercury electrode. By employing a medium with NH3-NH4Cl buffer, DMG and NaNO2 during determining the trace Co2+, any interferences of highly concentrated Zn2+ and other coexisting metal ions in the electrolyte are completely eliminated due to the selective masking effect of EDTA. When the concentration of Co2+ is within 1.0×10–10–3.2×10–7 mol/L range, it shows a good linear relationship with the current peak. Detection limit is 1.0×10–11 mol/L, and RSD ≤2.7% for six successive assays. We have compared the efficiency of the current method to that obtained by cobalt nitroso-R-salt spectrophotometry, and the absolute values of relative deviations are ≤4.2%. The method developed and described herein has been successfully employed in determining the trace Co2+ in actual zinc electrolyte.