DETERMINATION OF ULTRA-TRACE AMOUNTS OF SELENIUM(IV) BY MEANS OF A NEW REACTION SYSTEM - METHYL YELLOW AND HYDROGEN-PEROXIDE

A spectrophotometric method for the determination of selenium is descr ibed based on the selenium(IV)-catalyzed oxidation of methyl yellow wi th hydrogen peroxide in a nitric acid medium. As the redox reaction pr oceeds, the red color of methyl yellow is decolorized. The values of l ogA(0)/A show a good linear relationship with the amounts of selenium (A(0): absorbance of uncatalyzed. reaction solution; A: absorbance of catalyzed reaction solution.). The new method is extremely sensitive, as little as 2x10(-10) g ml(-1) can be easily measured. The detection range is from 5 x 10(-7) to 2 x 10(-10) g ml(-1). In addition, the sys tem possesses extremely high selectivity, most of ions including coppe r and tellurium can be tolerated during the determination of selenium. The method has been used to determine selenium in egg and wheat, and satisfactory results were obtained.