Determination of Se(IV) in the presence of Se(VI) at Ng Ml-1 concentration levels by a kinetic spectrophotometric method

The catalytic effect of Se(IV) on the reduction reaction of thionine(TN) by sulfide ion is used for determination of trace amounts of selenium(IV) ion by a kinetic-spectrophotometric method. This new method is simple and highly sensitive. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of the reaction mixture at 598 nm. The fixed time method was used for the first 45s from initiation of the reaction. Under the optimum conditions, in the concentration range of 2-90 ng ml(-1) of selenium(IV), a quite linear regression equation (r = 0.9984, n = 14) was obtained. The experimental detection limit of the method (S/N = 3) was 1.3 ng ml(-1). The relative standard deviation of ten replicate measurements is 2.51% for a 40 ng ml(-1) solution of selenium. The proposed method is used to the study of selenium (IV,VI) speciation in water at ng ml(-1) levels. This method was extended for the determination of selenium in real samples.