New spectrofluorimetric reagent, 2,3-diamino-1,4-dibromonaphthalene, for the determination of selenium in biological materials

Abstract

2,3-Diamino-1,4-dibromonaphthalene (Br₂-DAN) has been investigated as a new reagent for the spectrofluorimetric determination of selenium. It has advantages in comparison with the commonly used 2,3-diaminonaphthalene (DAN) as ligand. The values of the acidity constants of Br₂-DAN make the adjustment to the optimum pH for the piazselenol reaction easy, and the reaction can be performed in a strongly acidic medium. The stability of the reagent is good and there is no need to work in subdued daylight. In cyclohexane, the fluorescence of the selenium complex, 4,7-dibromo-5,6-benzopiazselenol, is measured at 577 nm and with excitation at 383 or 518 nm. The background is low and equivalent to less than 0.1 ng of selenium for excitation at the longer wavelength. An analytical procedure is presented for the determination of total selenium in small biological samples where the whole analysis is performed in a single test tube. The reduction of Se^VI to Se^IV is performed by hydrobromic acid at 85 °C over 15 min. This is followed by derivatization into piazselenol at 70 °C for 10 min. Iron(III) and copper(II) do not interfere.