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.

Keywords

catalytic adsorptive voltammetry / highly selective masking / Co²⁺ determination / zinc electrolyte

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