Sampling of dissolved inorganic SbIII by mercapto-functionalized silica-based diffusive gradients in thin-film technique

Abstract

The mercapto-functionalized silica (MPS) diffusive gradients in thin-film (DGT) devices, for the first time, were characterized by the determination of dissolved inorganic Sb^III. The performance of MPS–DGT was assessed by (1) determining the diffusion coefficient of Sb^III in polyethersulfone membrane, (2) assessing the uptake efficiency and digestion efficiency of MPS for Sb^III, (3) investigating the effect of pH, ionic strength (as NaNO₃) and foreign ions on the performance of MPS–DGT for Sb^III species, and (4) assessing the validation of MPS–DGT for the measurement of dissolved inorganic Sb^III in spiked water samples. The diffusion coefficient of Sb^III measured in the PES membrane by a diffusion cell was (3.05 ± 0.09) × 10⁻⁶ cm² s⁻¹. There was a tendency toward higher adsorption affinity for Sb^III compared with Sb^V. Mass vs. time measurements of MPS–DGT at pH 6 (0.01 mol L⁻¹ NaNO₃) demonstrated a linear uptake of Sb^III (R² = 0.9973). The performance of MPS–DGT was independent of ionic strength (0.001–0.7 mol L⁻¹ NaNO₃ at pH 5) and pH (3–8, 0.01 mol L⁻¹ NaNO₃) for the measurement of Sb^III. The presence of foreign ions (such as Ca^II, Mg^II, Cd^II, Zn^II, Cu^II, As^III and Sb^V) has no significant influence on the uptake of Sb^III by MPS–DGT. MPS–DGT can quantitatively measure the concentration of dissolved inorganic Sb^III in spiked etching wastewater. In spiked natural freshwater, the concentration of dissolved inorganic Sb^III obtained by MPS–DGT is significantly lower than the concentration of added Sb^III due to the presence of natural organic matter (8.7 mg C L⁻¹) which would have complexed a fraction of the added Sb^III and thereby changed the speciation of added Sb^III. The MPS–DGT device can potentially be used as a tool for speciation measurements of Sb^III in aqueous environments.