Spectrofluorimetric kinetic determination of selenium (IV) by flow injection analysis in cationic micellar medium

A sensitive catalytic kinetic spectrofluorimetric method for determining ng ml−1 of selenium by flow injection analysis has been developed. The method, based on the catalytic effect of Se (IV) on the reduction of resorufin by sulphide, in the presence of cetylpyridinium chloride, is monitored spectrofluorimetrically (λex=480 nm; λem=583 nm). The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated. The method is simple, rapid, precise, sensitive, and widely applicable. The limit of detection is 1 ng ml−1 Se (IV), and the calibration range is 5–1000 ng ml−1. Sampling rate is 60 samples h−1, and the relative standard deviation of 12 determinations of 100 ng ml−1 Se was 0.76%. The determination of Se (IV) in the presence of Se (VI) and total selenium is described. The method was applied to the determination of Se in selenium tablets, and several synthetic samples.