Simultaneous determination of Pb2+, Cd2+ and Zn2+ by adsorptive stripping voltammetry using Clioquinol as a chelating-adsorbent agent

• A sensitive and selective method for the determination of Pb, Cd and Zn is presented.
• The method is based on the adsorptive accumulation of Clioquinol complexes onto HMDE.
• Adsorptive and anodic stripping voltammograms with HMDE and HgFE were compared.
• All three metals gave peaks that were distinctly separated by about 200 mV.

A sensitive and selective method for the simultaneous determination of lead, cadmium and zinc based on the formation of their complexes with Clioquinol (5-chloro-7-iodo-8-hydroxyquinoline, CQ) is described. These studies were carried out using separate copper, lead, cadmium and zinc solutions and also mixtures of them. The optimum pH values were 2.3; 5.1; 5.3 and 5.2 for copper, lead, cadmium and zinc respectively (Britton Robinson buffer 0.03 mol L−1). In addition to optimum pH values, copper not interfere, but simultaneous determination of four elements is not possible. A pH of 5.3, a CQ concentration of 3.6 μmol L−1 and an accumulation potential of −0.65 V were chosen for the analysis. Copper, lead, cadmium and zinc complexes peak currents were observed at −0.30; −0.41; −0.59 and −0.95 V whereas the free CQ is reduced at –0.80 V. For individual analysis, the relationship between the peak current and metal concentration is linear until 40.0; 31.0 and 70.0 μg L−1 for lead, cadmium and zinc respectively. However in the simultaneous determination, the relationship is linear until 15.0 μg L−1 for lead and cadmium and 25.0 μg L−1 for zinc and the detection limits were found to be 0.10; 0.06 and 0.06 μg L−1 for lead, cadmium and zinc respectively. The relative standard deviation for 6 replicates determination of 5.0 μg L−1 lead, cadmium and zinc is equal to 1.8%, 0.9% and 1.6% respectively. The method was validated by determining lead, cadmium and zinc in spiked synthetic sea water (ASTM D665), Ontario lake reference water (TMDA-61.2) and was applied to the determination of these metal ions in tap water, sea water, and mineral water samples.