Keywords: heavy metals, trace metals, electrochemistry, soil pollution, chemical speciation, free metal activities, aqueous solutions, direct current voltammetry, DCV, cadmium, lead, copper, metal ion selective electrodes
A voltammetric method for determining free metal activities in aqueous solutions. Part 1: direct current voltammetry of Cd, Cu, and Pb
A selective and sensitive method for determining free metal activities (M2+) for Cd, Cu and Pb in aqueous solutions is presented based on the Lingane and DeFord and Hume models. Electrochemical and complexation studies were carried out by direct current voltammetry (DCV) and by metal ion selective electrodes (ISE) as a reference method. A voltammetric equation was tested to evaluate (M2+) by varying ligand type and pH (4.5–7.5). Experimental DCV-Nernstian slopes and R² values were 29.1, 0.887 for Cd2+, 29.1, 0.957 for Cu2+ and 27.6, 0.925 for Pb2+, respectively. Comparison of the two independent methods gave for the DCV-ISE plots, slopes and R² values of 0.823, 0.825 for Cd, 0.996 and 0,996, for Cu and 1.10 and 0.935 for Pb respectively. The DCV- and ISE-(M2+) values and those predicted by MINEQL+, using reported stability constants, were statistically similar. These studies are ecologically relevant as the method allows the assessment of chemical activities of essential and toxic free heavy metals in soil solution and other synthetic and natural solutions.