Combination of Diffusive Gradient in a Thin Film Probe and IC-ICP-MS for the Simultaneous Determination of CH3Hg+ and Hg2+ in Oxic Water

A diffusive gradient in thin film technique (DGT) was combined with ion chromatography and inductively coupled plasma mass spectrometry (IC-ICP-MS) for the in situ simultaneous quantification of CH3Hg+ and Hg2+ in aquatic environments. After diffusing through an agarose diffusive layer, the Hg species accumulated in a thiol-functionalized resin layer and were extracted using acidic thiourea solution to form stable thiourea–Hg complexes that were separated and detected via ion chromatography and ICP-MS, respectively. The effective diffusion coefficients of CH3Hg+ and Hg2+ complexes in the agarose diffusion layer with chloride were 5.26 (±0.27) × 10–6 and 4.02 (±0.10) × 10–6 cm2 s–1, respectively. The effective diffusion coefficients of CH3Hg+ and Hg2+ complexes in the agarose diffusion layer with dissolved organic matter was 3.57 (±0.29) × 10–6 and 2.16 (±0.19) × 10–6 cm2 s–1, respectively. The practical method detection limits are 0.1 and 0.7 ng L–1 for CH3Hg+ and Hg2+ respectively for three weeks deployment. Lower detection limits would be possible by employing a thinner agarose diffusive layer and/or by deploying the probes longer. The method can measure time averaged CH3Hg+ and Hg2+ concentrations simultaneously in oxic water, making it useful as an in situ monitoring tool.