Speciation of inorganic selenium in natural water by in situ solid-phase extraction using functionalized silica

Abstract

Functionalized adsorbents with poly-(4,9-dioxododecane-1,12-guanidine) (SiO₂–PDDG) and mercaptophenyl groups (MPhS) were used for the separation of Se(VI) and Se(IV) for the first time. Fixation of PDDG was characterized by capillary electrophoresis and TGA/DSC. The quantitative extraction of Se(VI) proceeded due to anion exchange at pH 3–7. The adsorption capacity of SiO₂–PDDG for Se(VI) was 28 μmol g⁻¹. Silicas with mercaptophenyl groups were used for the extraction of Se(IV) from solutions in the range of 2 M HCl – pH 6.5. The adsorption capacity of MPhS was 35 μmol g⁻¹. A system of columns containing synthesized adsorbents was proposed for the separation of Se(VI) and Se(IV) and their subsequent determination by ICP-MS. Optimal parameters of adsorption include a flow rate of 1 mL min⁻¹, pH of 5, and sample volume of 200 mL. Se(IV) was desorbed with 5 mL of 0.25 M 2,3-dimercapto-1-propanesulphonic acid and Se(VI) with 5 mL of 1 M HNO₃. The preconcentration factor was 40. The limits of detection (3s) were 0.75 and 1.25 ng L⁻¹ for Se(VI) and Se(IV), respectively. The proposed method (SPE-ICPMS) was used to determine selenium species in natural water and certified reference materials. The separation was carried out directly at the sampling site.