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Organizations & People
Pure Appl. Chem. Vol.
73, No. 1, pp. 9-15 (2001)
Pure and Applied
Vol. 73, Issue
In situ speciation measurements. Using diffusive gradients in thin
films (DGT) to determine inorganically and organically complexed metals*
Hao Zhang and William Davison
Department of Environmental Sciences, Lancaster University,
Lancaster, LA1 4YQ, UK
Abstract: The possibilities of using diffusive gradients in
thin films (DGT) and anodic stripping voltammetry (ASV) to perform speciation
measurements in natural waters are discussed. Both techniques measure
labile species, but different approaches have been used to discriminate
organic (Corg) and inorganic (Cinorg) metal complexes. In DGT, metals
are bound to a resin after passing through a hydrogel that serves as
a well-defined diffusion layer. DGT devices with different hydrogels
that impede the diffusion of humic substances by different amounts were
deployed in solutions of copper and humic substances. Devices with a
gel composition that greatly restricted the diffusion of humic substances,
but only retarded the diffusion of Cu ions slightly, could be used directly
to determine Cinorg. By using different, more open pored gels, which
allowed some passage of humic substances, it was possible to determine
both Corg and Cinorg. The two separate measurements of Cinorg obtained
using the two DGT approaches agreed well. At the high concentrations
of Cu used there was good agreement with the predicted distribution
from the speciation code WHAM. At the lowest Cu concentration, the proportion
of Cinorg estimated using DGT was higher than with WHAM. Possibilities
of errors in the DGT or modeling approaches are discussed.
* Lectures presented at the 11th European
Conference on Analytical Chemistry (EUROANALYSIS XI), Lisbon, Portugal,
3 9 September 2000. Other presentations are published in this
issue, pp. 1-54.
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