DETERMINATION OF SELENIUM(IV) AND SELENIUM(VI) IN WATER SAMPLES BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY AFTER COLLECTION AS 3-PHENYL-5-MERCAPTO-1, 3, 4-THIADIAZOLE-2(3H)-THIONE SELENIUM(IV) COMPLEX ON ACTIVATED CARBONE

This method is based on the direct heating of activated carbon (AC) collected selenium(IV)-3-phenyl-5-mercapto-1,3,4-thiadiazole-2(3H)-thione (Bismuthiol II) complex: that is, AC is introduced directly as "AC-suspension" into the graphite tube atomizer, without the desorption of seienium from AC. For the determination of selenium(IV), conc. hydrochloric acid is added to the sample solution containing less than 0.5-mu-g of selenium(IV) at a final concentration of 1.5 M, and then, 5 cm3 of 0.1% Bismutiol II solution is added, and the solution is stirred for 5 min. for formation of complex. Further, 50 mg of AC is added and one is stirred for 5 min. for the collection of complex. After separation of AC from the aqueous phase through a membrane filter, An AC-suspension is prepared by adding 5.0 cm3 of water to the AC. 10-mu-l of Rh solution (500-mu-g Rh/cm3) is injected into the graphite tube and is previously heated. Then, aliquots (10-mu-l) of AC-suspension is injected into the graphite tube and selenium peak height is measured under the optical instrumental operating conditions. Selenium(VI) is collected by same procedure after reduction to selenium (IV) by potassium bromide in the presence of hydrochloric acid. The determination limit was 0.02-mu-g/1000 cm3 (S/N = 3), and relative standard deviation (0.25-mu-g/100 cm3) was 3 approximately 4% (n = 6). This method was applied to the determination of selenium(IV) and selenium(VI) in well water and rain water.