Abstract:

The anodic stripping semidifferential electroanalysis technique with thin mercury film electrode in situ was used for the direct determination of traces of Pb and Cd in the presence of Sn. With 1:5 lactic acid (pH=5) as supporting electrolyte, Pb and Cd gave well-defined e-E curves. As expected from theory, the shape having a minimum and a maximum was observed in each e vs. E curve. The ratio of minimum e values to maximum ones were 2.18 for Pb(Hg) and 2.31 for Cd(Hg), respectively. The negative peak potential, E_np, was independent of ionic concentration and is -0.57V vs. S. C. E. for Pb(Hg) and -0.75V for Cd(Hg). The width between the negative peak and positive one, W_PP was also independent of ionic concentration and experimental values of W_PP for Pb(Hg) and Cd(Hg), and agreed well with the theoretical value of 32 mV. The height from the negative peak to positive one, e_pp, was linear with V^1.5. It was also linear with pre-electrolysis time at rotating electrode between 3-6 min. The linear calibration curves were obtained for 2.00×10^-8-1.20×10^-7 g Pb/ml and 2.00×10^-9-1.20×10^-7 g Cd/ml. All theoretical predictions concerning anodic stripping semidifferential electroanalysis have been adequately confirmed. As for the experimental determination, sample solution was pipetted into cell and the electrodes were insetred, deaerated. After pre-electrolysis at -1.0V vs. S. C. E. for 3 min. and a subsequent 30 sec. delay, the potential was scanned from -1.0V to +0.5V vs. S. C. E. The amounts of Pb(Ⅱ) and Cd(Ⅱ) ions were then determined by the standard addition. It is possible to recover 105±6% for Pb and 97±4% for Cd. Co(Ⅱ), Cr(Ⅲ), Fe(Ⅲ), Ni(Ⅱ), Zn(Ⅱ) and small amount of Bi(Ⅲ), Cu(Ⅱ) and Sb(Ⅲ) did not interfere under the experimental conditions. The method was rapid and reproduceable.