Determination of trace elements in zinc electroplated films by differential pulse anodic stripping voltammetry after dissolution with acids

A method for determining 480 mg m-2of Tl, Pb, Cd, Sn, In, Cu and Sb in zinc electroplated films on steel sheets has been developed. Although (1+9)H2SO4 containing 100 μg cm-3 of N, N-dimethylthiourea (Acid A) was capable of dissolving the films without dissolution of the steel sheets, Sb was reduced in the presence of nascent hydrogen to escape as volatile SbH3 and Cu was incompletely dissolved to remain on the steel sheets. Dissolution with conc. HNO3 under cooling resulted in the complete recovery of Sb and Cu, although the steel sheets were dissolved a little. Therefore, dissolution with Acid A was adopted for the determination of Tl, Pb, Cd, Sn and In, and conc. HNO3 for Cu and Sb. Nitric acid was removed by fuming with H2SO4 after dissolution of the films. Thallium, Pb, Cd, Sn, In, Cu and Sb were determined by differential pulse anodic stripping voltammetry according to the procedure described in a previous paper. A relative standard deviation (n=5) of about 3% was obtained. In addition, the quantities of these elements in the films were correlated with the concentrations of the elements in the electroplating baths.