Ultrasensitive Fluorimetric Detection of Trace Se(IV) as 4,5-Benzopiazselenol on Nonpolar Adsorbents

A method for separating Se(IV) from Se(VI) has been proposed. The method is based on the formation of fluorescent 4,5-benzopiazselenol (a complex of Se(IV) with 2,3-diaminonaphthalene), which was quantitatively extracted in dynamic mode from aqueous solutions using glass preconcentrating cartridges filled with nonpolar adsorbents: SiO₂-C8, SiO₂-C16, SiO₂-C18, and SiO₂-HPh. The increase in the fluorescence intensity of the adsorbent in the preconcentrating cartridge with increasing concentration of 4,5-benzopiazselenol on its surface was used to develop a method for the solid-phase extraction (SPE)-fluorimetric determination of Se(IV) with a detection limit of 2 ng per 0.025 g of SiO₂-С16 adsorbent. When using 10 mL of solution, the detection limit was 0.2 ng mL^-1 (0.2 μg L^-1), and when using 100 mL of solution, it was 0.02 ng mL^-1 (0.02 μg L^-1). The linearity of the calibration graph was maintained up to 2 μg per 0.025 g when using the SiO₂-C16 adsorbent. Se(VI) did not form a complex with diaminonaphthalene and was not extracted by nonpolar adsorbents. Se(VI) passing through the preconcentrating cartridge can be determined in the effluent by ICP-MS.