DETERMINATION OF TOTAL SELENIUM AND DISSOLVED SELENIUM SPECIES IN NATURAL-WATERS BY FLUOROMETRY

A method for the determination of total selenium and dissolved seleniu m species at nanogram levels in natural water samples was developed. S elenite and selenate were separated through a Dowex AG2-X8 column, and dissolved hydrophobic base, acidic, and neutral organic selenium were separated by an XAD-8 column. The elution or a water sample of 50-200 mL with nitric acid addition (2.5 mL/L) was evaporated on an electric plate and digested with HNO3/HClO4 (2/1, v/v). After being reduced wi th HCI and complexed with 2,3-diaminonaphthalene, the fluorophore was extracted into cyclohexane, and its fluorescence was measured. The rec overy of selenium added to 50 mL of river water was 97.9-104%, with an average of 99.9% (n = 20). The detection limit of the method for wate r total selenium was 0.35 ng of selenium (blank + 2 SD), and the preci sion of the method for natural water samples with selenium concentrati ons ranging from 28 to 115 ng/L was 2.1%. For individual dissolved sel enium species, the detection limits were all lower than 1.8 ng.