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RESEARCH ARTICLE
Contents Vol 5(1)

Trace metal dynamic speciation studied by scanned stripping chronopotentiometry (SSCP)

Rute F. Domingos A B E , Rócio Lopez A C and José P. Pinheiro D
+ Author Affiliations
- Author Affiliations

A CMQA, Departamento de Química e Bioquímica, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, PT-8005-139 Faro, Portugal.

B Present address: Faculté des arts et des sciences, Département de chimie, Université de Montréal, C.P. 6128, succursale Centre-ville, Montréal, QC H3C 3J7, Canada.

C Present address: Instituto de Investigaciones Agrobiológicas de Galicia, CSIC, Avd. De Vigo s/n, Campus Universitario Sur, E-15780 Santiago de Compostela, Spain.

D CBME, Departamento de Química e Bioquímica, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, PT-8005-139 Faro, Portugal.

E Corresponding author. Email: ri.ferreira.domingos@umontreal.ca

Environmental Chemistry 5(1) 24-32 https://doi.org/10.1071/EN07088
Submitted: 28 November 2007  Accepted: 4 January 2008   Published: 22 February 2008

Environmental context. Natural aquatic systems are subject to changing conditions and practically never reach chemical equilibrium. Therefore, a quantitative understanding of the interaction of the trace metals with heterogeneous samples and their kinetic characteristics requires the dynamic characterisation of trace metal speciation. We show that scanned stripping chronopotentiometry (SSCP) is able to discriminate the dynamic nature of the complexes, although it still overestimates the average stability constants obtained from the SSCP wave characteristics using the Freundlich isotherm to account for the chemical heterogeneity.

Abstract. The ability of scanned stripping chronopotentiometry (SSCP) to obtain dynamic information for metal complexation with heterogeneous colloidal ligands was evaluated by measurements of lead(II) and cadmium(II) complexation by humic and fulvic acids extracted from an ombrotrophic peat bog. Average stability constants were calculated, using a first order chemical heterogeneity approach, and compared with those obtained by an ion selective electrode (ISE). SSCP average stability constants were overestimated in comparison to those obtained by the ISE, which suggests that the first order heterogeneity approach did not fully account for the ligand heterogeneity. However, the comparison of the stability constants obtained from the two SSCP signals (the shift of the half-wave potential and the decrease of transition time) provides information about the dynamic nature of the metal complexes formed with the humic matter. These results were in reasonable agreement with the theoretical predictions of the dynamic theory for colloidal systems.

Additional keywords: colloidal dispersion, humic substances, lability, scanned stripping chronopotentiometry, speciation.


Acknowledgements

This work was performed within the framework of the project POCI/QUI/56845/2004. A Ph.D. grant to Rute Ferreira Domingos (SFRH/BD/8366/2002) and a Pos-Doc grant to Rócio Lopez (SFRH/BPD/20176/2004) from Fundação para a Ciência e Tecnologia, Portugal are acknowledged.


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Accessory material

An example of the SSCP raw data obtained for the lead interaction with humic and fulvic acid at 0.01 and 0.1 M ionic strength is available from the author or Environmental Chemistry.