Title: 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

Authors: Arturo Aguirre-Gomez, Murray B. McBride, Wendell A. Norvell

Addresses: Departamento de Quimica, Universidad Nacional Autonoma de Mexico, F.E.S.-Cuautitlan, Apartado Postal 149, Cuautitlan, Mexico 54800, Mexico. ' Cornell University, 910 Bradfield Hall, Ithaca 14853, NY, USA. ' USDA-ARS Plant, Soil and Nutrition Laboratory, Tower Road, Ithaca NY 14853, USA

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.

Keywords: chemical speciation; chemical activity; metal buffer solutions; heavy metals; trace metals; electrochemistry; soil pollution; chemical speciation; free metal activities; aqueous solutions; anodic stripping voltammetry; DCV; cadmium; lead; copper; zinc.

DOI: 10.1504/IJEP.2006.009099

International Journal of Environment and Pollution, 2006 Vol.26 No.1/2/3, pp.68 - 89

Available online: 02 Mar 2006 *

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