Evaluation of a mercapto-functionalized silica binding phase for the selective sampling of SeIV by Diffusive Gradients in Thin films

International audience; This study evaluates binding discs based on 3-mercaptopropyl-functionalized silica gel for the selective sampling of selenite (Sew) using Diffusive Gradients in Thin films sampler (DGT). Selv accumulation was quantitative and selective over Sew and followed the theoretical linear accumulation with the exposure time up to 0.7 pg. The sampling was not affected by ionic strength variations down to 10-2 mol L-1 (as NaNO3) but Sew accumulation was found to decrease significantly for pH greater than 5 and was nearly zero at pH 9. Both the limited accumulation range and the pH dependence were unexpected because they have not been reported in the literature related to the Se"' trapping by thiol-based solid phases. Our experiments showed that after Sew was bound to thiol functional groups, a further pH-dependent reaction occurred with free thiols, resulting in the reduction of Sew into elemental selenium (Se) followed by its release and back-diffusion through the DGT sampler. Unfortunately, such a reversible accumulation is incompatible with the implementation of the mercapto-functionalized silica binding phase in DGT devices for Sew selective sampling.