Selective determination of soluble inorganic selenium (IV), (VI) and organic selenium in soil

Soil extracts containing appreciable amounts of dissolved organic compounds often present difficulties in their analysis for selenium. As a method for eliminating the difficulties, the addition of a small amount of copper ion to the soil extracts was found to be effective for suppressing interference caused by the organic compounds in the extracts. By applying this result, a method for the fractional determination of selenium in soil extracts was developed. Selenium(IV) was determined by HPLC with fluorescence detection after reaction with 2, 3-diaminonaphthalene. Selenium(VI) was first reduced to the quadrivalent state with potassium bromide and hydrochloric acid as reducing reagents and copper ion, then the total inorganic selenium was determined by the same method as the determination of selenium(IV). The amount of selenium(VI) was calculated by subtracting the amount of selenium(IV) from the total inorganic selenium. Total selenium in the soil extract was also determined by the same method as the total inorganic selenium after oxidizing the organic compounds in the extract. The amount of organically-bound selenium was estimated from the difference between the total selenium and the total inorganic selenium. The proposed method could be applied to the fractional determination of selenium in the soil extract with satisfactory reproducibility and recovery.