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 high ly sensitive. The reaction was monitored spectrophotometrically by measurin g the decrease in absorbance of the reaction mixture at 598 nm. The fixed t ime method was used for the first 45s from initiation of the reaction. Unde r the optimum conditions, in the concentration range of 2-90 ng ml(-1) of s elenium(IV), a quite linear regression equation (r = 0.9984, n = 14) was ob tained. 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 t o the study of selenium (IV,VI) speciation in water at ng ml(-1) levels. Th is method was extended for the determination of selenium in real samples.