Gold nanoparticle-based colorimetric assay for inorganic selenium speciation analysis in drinking water by solid-phase microextraction mediated dielectric barrier discharge vapor generation

A sensitive colorimetric assay for the speciation analysis of inorganic Se(IV) and Se(VI) in drinking water samples was proposed in this work. In this assay, solid-phase microextraction with nano-TiO₂ as adsorbent was employed for the selective enrichment of Se(IV) in water with solution pH values ranging from 4 to 7. Then, dielectric barrier discharge induced vapor generation was used to generate volatile H₂Se vapor from Se(IV) adsorbed on nano-TiO₂. Finally, gold nanoparticles (AuNPs) were utilized to induce a color change upon the introduction of H₂Se vapor for Se(IV) determination. The Se(VI) concentration was determined by pre-reduction and subtraction. With this assay, the enrichment and speciation analysis of Se(IV) and Se(VI) in water samples could be realized simultaneously. The experimental parameters that influence the adsorption, vapor generation, and color change were evaluated in greater detail. Under optimal conditions, the relative standard deviation for Se(IV) was 1.1 % at a concentration of 50 μg L⁻¹ and the detection limit for Se(IV) was 0.31 μg L⁻¹ with 50 mL sample volume and 0.16 μg L⁻¹ with 100 mL sample volume by UV–Vis detection. Compared with the AuNPs colorimetric assays with hydride generation and photochemical vapor generation, this assay exhibits a lower detection limit of Se and a greater resistance to interference. With these advantages, this method was proved to be applicable for accurate determination of Se(IV) and Se(VI) in drinking water samples such as purified water samples and Se-enriched natural mineral water samples.