Determination of Selenium Species in Water by Controlled Temperature Digestion-Hydride Generation-Atomic Fluorescence Spectrometry

10.00 mL of water sample were taken and heated to evaporate to near dry at 60-70℃, 2.0 mL of mixed acid of nitric acid and perchloric acid (1+1) were added, and the mixture was heated until white smoke was exhausted. After 2.0 mL of hydrochloric acid was added, the mixture was shaked well and heated to keep slight boiling for 3-5 minutes. After cooling, the solution was transferred to a colorimetric tube and made up to 10.00 mL with deionized water. The total selenium content was determined by hydride generation-atomic fluorescence spectrometry. Another 10.00 mL of water sample were taken, and 2.0 mL of hydrochloric acid were added. After the mixture was heated at 60-70℃ until the solution volume were less than 5 mL, the solution was transferred to a colorimetric tube and made up to 10.00 mL with deionized water. The content of inorganic selenium (the sum of tetravalent selenium and hexavalent selenium) was determined by hydride generation-atomic fluorescence spectrometry. Another 5.00 mL of water sample was taken into a 10 mL colorimetric tube, 2.0 mL of hydrochloric acid was added, and the volume was made up to 10.00 mL with deionized water to determine the content of tetravalent selenium by hydride generation-atomic fluorescence spectrometry. The total selenium content minus the inorganic selenium content was the organic selenium content, and the inorganic selenium content minus the tetravalent selenium content was the hexavalent selenium content. Under the optimal working conditions of the instrument, the mass concentration of selenium was linearly related to the corresponding fluorescence intensity in the range of 1.00-20.0 μg·L^-1. The detection limit (3s) and the lower limit of determination (10s) of selenium were 0.11, 0.36 μg·L^-1, respectively. The method was applied to determination of total selenium, inorganic selenium and tetravalent selenium in water of an area, giving recovery obtained by standard addition method between 95.7% and 104%, and RSDs (n=6) in the range of 1.9%-3.2%. The total selenium, inorganic selenium and tetravalent selenium in water from different regions were determined by this method, and the contents of organic selenium and hexavalent selenium were obtained by calculating with subtraction method.