A 9.0 mL aliquot of synthetic sea water (ASTM D665) contaminated with a standard solution containing lead, cadmium and zinc (5.0 μg L−1), was added to the electrochemical cell that contained 1.0 mL of BR buffer and 30 μL of CQ 1.2 mmol L−1 adjusting to the 5.3 pH with NaOH solution. The analysis of these metal ions was carried out using the standard addition method. The values obtained were 4.8 ± 0.3; 5.0 ± 0.1; 4.9 ± 0.2 μg L−1; (RE −4.0%, 0.0% and −2.0%) respectively for lead, cadmium and zinc. The usefulness of the present method was also evaluated by determining these analytes in certified reference water TMDA-61. Fig. 6 shows differential pulse voltammograms and calibration plot obtained when 0.5 mL of TMDA-61 sample was added to 8.5 mL of deionized water, 1.0 mL of BR buffer pH 5.3 (0.3 mol L−1) and 30 μL of 1.2 mmol L−1 CQ. The values obtained for lead, cadmium and zinc were 65.6 ± 1.2; 59.5 ± 0.6; 69.9 ± 0.9 μg L−1; (RE 6.8%, 2.6% and −2.0%). These values are satisfactory because this reference lake Ontario water contains about 28 metal ions with concentrations between 3.2 and 113 μg L−1.