Titanium dioxide-based DGT for measuring dissolved As(V), V(V), Sb(V), Mo(VI) and W(VI) in water

A titanium dioxide-based DGT method (Metsorb-DGT) was evaluated for the measurement of As(V), V(V), Sb(V), Mo(VI), W(VI) and dissolved reactive phosphorus (DRP) in synthetic waters. Mass vs. time DGT deployments at pH 6.06 (0.01 mol L−1 NaNO3) demonstrated linear uptake of all analytes (R2≥0.994). Diffusion coefficients measured using a diffusion cell were in reasonable agreement with diffusion coefficients measured using DGT samplers (DCell/DDGT=0.82–1.10), although a systematic difference was apparent. The Metsorb-DGT method was independent of ionic strength (0.001–0.7 mol L−1 NaNO3 at pH 7.1) for the measurement of all analytes (CDGT/CSol=0.88–1.11) and, with the exception of V(V), the method was independent of pH (3.98–8.24, 0.01 mol L−1 NaNO3), indicated by CDGT/CSol values in the range 0.88–1.13 for short-term deployments (up to 10 h). For V(V) at pH 3.98, Metsorb-DGT underestimated the solution concentration by 17%, presumably due to weak binding of the VO2+ species. The Metsorb-DGT and ferrihydrite-DGT (in situ precipitated ferrihydrite) methods were compared by deploying samplers in synthetic freshwater (pH 7.20, conductivity 223 μS cm−1) and synthetic seawater (pH 8.3. salinity 34.6) for up to four days. For synthetic freshwater, CDGT/CSol values between 0.87–1.17 were obtained for all analytes measured by the Metsorb-DGT method over the deployment period. For ferrihydrite-DGT, CDGT/CSol values between 0.97–1.23 were obtained for As(V), V(V), W(VI) and DRP. However, Mo and Sb(V) showed reduced uptake and CDGT/CSol values were in the range 0.18–1.14 and 0.39–0.98, respectively. In synthetic seawater deployments, Metsorb-DGT was capable of measuring As(V), V(V), Sb(V), W(VI) and DRP for up to 4 days (CDGT/CSol=0.89–1.26), however, this method was not capable of measuring Mo for deployment times >4 h (CDGT=0.27–0.72). For ferrihydrite-DGT, CDGT/CSol values in the range 0.92–1.16 were obtained for As(V), V(V) and DRP, however, Mo(VI), Sb(V) and W(VI) could not be measured to within 15% of the solution concentration (CDGT/CSol 0.02–0.83).