Indirect Determination of Zinc in Zinc Supplementation Tablets by Coulometric Titration

1.0 mol·L^-1 potassium iodide-sodium tetraborate solution (pH 9.2) was used as supporting electrolyte solution, and platinum electrodes were used as electrolysis electrode and indicating electrode. After 10 s of iodine formation by electrolysis in room temperature, the sample solution of zinc supplementation tablet was added to titrate residual cysteine. Endpoint of titration was indicated by coulometric titration. Zinc in the sample solution was indirectly determined according to Faraday's law of electrolysis. Linear relationship between values of quantity of electricity of consumption and mass concentration of zinc was obtained in the range of 0.05-0.50 g·L^-1, with detection limit (3s) of 0.04 mg·L^-1. The proposed method was applied to the analysis of the samples of zinc supplementation tablets, giving values of RSDs (n=6) of determined values in the ranges of 0.76%-0.92%. There was no significant difference between the determined value and the labeled amount.