Abstract

A sensitive voltammetric method is reported for the simultaneous determination of Pb2+ and Cd2+ using a nafion-guanine-coated mercury film glassy carbon electrode. This modified electrode exhibited well-developed signals for the reduction of the adsorbed complexes Pb-Guanine and Cd-Guanine, at -0.59 and -0.76 V respectively. The effects of parameters such as pH, accumulation potential and time (E-acc, t(acc)) were optimized. These studies were done using metallic ions on their own and also mixed together. The best pH for the individual analysis of Pb2+ or Cd2+ were 2.2 and 6.1 respectively, whereas a pH of 5.0 (acetate buffer 0.01 mol L-1) was chosen for simultaneous determination. Under the optimized conditions (pH = 5.0; t(acc) = 60 s; E-acc = -1.0 V) reduction signal was found to be proportional to the concentration of Pb2+ and Cd2+ over the 6.6-35.0 mu g L-1 range, with 36 detection limits (DL) of 2.2 and 4.6 mu g L-1. However, for lower concentrations, a time of 120 s was applied, yielding a linear range from 0.5 to 12.0 mu g L-1 with DLs of 0.26 and 0.25 mu g L-1 for Pb2+ and Cd2+, respectively. If the guanine (G) is in the solution, the signals are much lower than in the modified electrode. The method was validated by determining Pb2+ and Cd2+ in certified reference material (GBW08607) and synthetic sea water (ASTM D665), spiked with 22 metal ions, with satisfactory results. Subsequently, the method was applied in bottled mineral waters and sea water samples without previous treatment.