Fluorometric Determination of Inorganic Selenium(IV), Selenium(VI) and Organic Selenium in Natural Waters

摘要

A method for the simultaneous determination of selenium species such as selenium(IV), selenium(VI) and organic selenium in natural waters has been developed in this paper. Selenium(IV) was fluorometrically determined after extracting the complex of 2, 3-diaminonaphthalene (DAN) into cyclohexane. Selenium(VI) in the sample was first reduced to the quadrivalent state by adding potassium bromide in 1.3M hydrochloric acid solution, then the total inorganic selenium was determined by the same technique as the determination of selenium(IV). The amounts of selenium(VI) can be calculated by subtracting the amounts of selenium(IV) from the total inorganic selenium. Organic selenium was determined as follows: all selenium, including inorganic selenium(IV), selenium (VI), and organic selenium, was coprecipitated with tellurium(IV), and then reduced to elemental selenium and tellurium by hydrazine sulphate in acid solution (4M HCl for river water samples; 1-2M HCl for sea water samples). The elemental selenium and tellurium were dissolved in a mixture of nitric acid and hydrochloric acid, reduced to selenium(IV) by boiling with 6M hydrochloric acid, and also determined by the DAN fluorometry. The amount of organic selenium was estimated by substracting the amount of both selenium(IV) and selenium(VI) from the total amount of selenium determined by this coprecipitation method. Interesting results were obtained from applying this method to river- and sea-water samples.