Anal. Chem. 2010, 82, 8903–8909
Performance Characteristics of Diffusive Gradients in Thin Films Equipped with a Binding Gel Layer Containing Precipitated Ferrihydrite for Measuring Arsenic(V), Selenium(VI), Vanadium(V), and Antimony(V) Jun Luo,† Hao Zhang,*,† Jakob Santner,†,‡ and William Davison† Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, United Kingdom, and Rhizosphere Ecology and Biogeochemistry Group, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences, Peter-Jordan-Strasse 82, 1190 Vienna, Austria Measurements at high spatial resolution by DGT (diffusive gradients in thin films) require a binding agent that is homogeneously distributed in the binding layer. Formation of ferrihydrite by in situ precipitation within a hydrogel has been previously shown to meet these requirements for the measurement of oxyanions by DGT. Here, we report for the first time detailed performance characteristics of the binding gel and associated DGT devices obtained by deployment in known solutions. To allow comparison of measured and theoretical accumulation of As(V), Se(VI), V(V), and Sb(V), their diffusion coefficients were determined using an independent diffusion cell. Theoretical responses were obtained irrespective of ionic strength (1-100 mmol L-1) and pH (3-8), except for Se above pH 7.8 and V below pH 5. Calculated detection limits, based on deployment times of 1 day, were lower than those for devices made with a binding gel cast with a ferrihydrite slurry, and the measured capacity of the binding layer was also superior. There was no evidence for interference from other oxyanions, but binding performance showed some deterioration after 38 days of storage. The potential capability for measuring labile forms of these oxyanions in acidic to neutral, fresh to brackish waters was demonstrated. Arsenic, selenium, vanadium, and antimony are often present in well oxygenated environments as oxyanions with oxidation states of +5, +6, +5, and +5, respectively. For the pH range of most natural waters, H2AsO4- is dominant below pH 6.5, whereas HAsO42- is dominant above 6.5.1 The main species of selenium is SeO42-.2 The dominant species of vanadium at lower total solution vanadium (
