Spectrophotometric determination of selenium based on catalytic reaction of methyl violet with sulfide

A rapid, simple, and sensitive spectrophotometric method for the determinat ion of trace amounts of selenium is described. The method is based on the c atalytic effect of Se(IV) on the reaction of Methyl Violet with sulfide at pH 8. The reaction was monitored spectrophotometrically by measuring the de crease in absorbance at 590 nm by a fixed time method. Selenium is determin ed in the range 80-1800 ng/mL. The limit of detection is 42 ng/mL and the r elative standard deviation for 10 determinations of 600 ng/mL of selenium i s 1.21.%. Selenium(IV) in the presence of selenium(VI) and total selenium i s determined by the method. The proposed method is successfully applied to the determination of selenium in water and in a health care product.