A voltammetric method for determining free metal activities in aqueous solutions. Part 2: anodic stripping voltammetry of Cd, Cu, Pb and Zn in synthetic and soil solutions
by Arturo Aguirre-Gomez, Murray B. McBride, Wendell A. Norvell
International Journal of Environment and Pollution (IJEP), Vol. 26, No. 1/2/3, 2006

Abstract: Theory and methodology for determining the free metal activity, (M²⁺), of Cd, Cu, Pb and Zn by anodic stripping voltammetry is presented. Metal-buffer solutions were prepared to control (M²⁺), which was varied by using different ligands and by changing pH. Total metal aqueous concentration of 10^-6–10^-7M and metal-ligand ratios of 1:20M, 0.010M acetate medium were used. Equations for reversible and irreversible systems were interpreted to explain the results. For Cd and Pb (pPb < 10), agreement was found among theory, experimental ASV and (M²⁺), calculated by using a speciation chemical equilibria programme and stability constants reported in the literature. Kinetic effects were observed for values of pPb > 10. For Cu and Zn, good agreement was found between the theory and calculated (M²⁺), and between experimental ASV results and calculated (M²⁺). Experimental ASV results showed Nernstian parallel shifts with regard to theory. Free metal activities in the order of pCd = 12, pCu = 18, pPb = 10 and pZn = 9 were measurable under the experimental conditions tested. Results too showed good agreement between Cu-ISE and Cu-ASV when measuring the free Cu²⁺ activity in aqueous extracts of four soils. Values of soil-(Cu²⁺) measured were in the order of 10^-5–10^-9.

Online publication date: Thu, 02-Mar-2006

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