Rapid one-step derivatization of Se(VI) to a piazselenol for the spectrofluorimetric determination of selenium in biological material
A spectrofluorimetric method for the determination of total selenium in biological samples has been developed. After oxidative destruction, the sample is reacted with a mixture of bromide and 2,3-diamino-1,4-dibromonaphthalene (Br2-DAN) without pH adjustment. Selenium(VI) is rapidly reduced by bromide to Se(IV) which then forms 4,7-dibromo-5,6-benzopiazselenol (Br2-DAN-Se). The conversion of Se(VI) to Br2-DAN-Se is completed in 6 min at 100°C. The piazselenol is extracted to cyclohexane and the fluorescence measured at 577 nm with excitation at 518 nm. The procedure has been validated by determinations on reference materials with selenium concentrations ranging from 4 to 1460 ng g−1. The advantages of the method are the fast reduction of Se(VI) by hydrobromic acid and the properties of Br2-DAN, which permit the piazselenol formation to be carried out in a strongly acidic medium and at high temperature. The limit of detection is 0.6 ng g−1 as estimated by three times the standard deviation of the blank determination (n = 7). The rate of reduction of Se(VI) to Se(IV) in hydrobromic acid was investigated as a function of concentration and temperature. The new kinetic data together with previous kinetic and equilibrium data for the piazselenol formation were used to model and optimize the simultaneous reduction-derivatization procedure.