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.

摘要

本文报道了一个直接测定高浓度锌电解液中痕量钴的选择性方法。该方法基于测定Co²⁺在滴汞 电极表面与丁二酮及亚硝酸盐络合产生的催化吸附极谱的二阶导数波建立起来的。利用NH₃–NH₄Cl 缓冲剂,DMG 及NaNO₂ 组成的底液测定痕量钴时。由于EDTA 的选择性掩蔽作用,电解液中高浓度 锌及任何其他金属离子的干扰都能完全排除。当Co²⁺浓度在1.0×10^–10~3.2×10^–7 mol/L 范围时,与峰电 流有良好的线性关系,检出限为1.0×10^–11 mol/L,RSD≤2.7%。将本法与亚硝基红盐显色法测定的结果 进行了比较,相对偏差的绝对值≤4.2%。本文提出的方法已成功用于实际锌电解液中痕量钴的测定。