Abstract: A spectrophotometric method for the determination of selenium (IV) is described, based on the selenium (IV)- catalyzed oxidation of dimethyl yellow with potassium bromate in 0.004 mol/L nitric acid solution medium and in the presence of OP emulsifier(p-iso-octyl phenoxy polyethoxy ethanol). As the redox reaction proceeds, the red color of dimethyl yellow is decolorized. The value of ΔA shows a good linear relationship with the amounts of selenium (IV) (A0: absorbance of uncatalyzed reaction solution; A: absorbance of catalyzed reaction solution). The results show that the maximum absorption is at 530 nm and the detection limit of the method for Se(IV) is 0.015μg/L. Beer’s law is obeyed for Se (IV) in the range of 0.00～0.80μg/L. The recoveries are 98.0%～102.5%, and the relative standard deviations (RSD) are 2.6%～4.3%. The method has been applied to the determination of trace selenium (IV) in egg and wheat samples, and satisfactory results were obtained.

Key words: selenium, catalytic spectrophotometry, foodstuffs, dimethyl yellow, potassium bromate