Determination of trace amounts of selenium in zinc sulfide by synchronous first-derivative fluorescence spectrometry

Abstract

A method for the determination of selenium in zinc sulfide by synchronous first-derivative fluorometry is described. This method is based on the formation of fluorescent 4, 5-benzopiazselenol by the reaction of selenium with 2, 3-diaminonaphthalene(DAN). The pretreatment conditions for dissolving zinc sulfide has been investigated in detail in order to obtain a good recovery of selenium. We used this method to suppress the interference of impurities in DAN. The recommended procedure is as follows: Take 50 mg of zinc sulfide into a flask with a reflux condenser. After addition of 20 ml conc. nitric acid into the flask, the sample solution is heated to dissolve the liberated sulfur. The sample solution is concentrated to about 1 ml by evaporation. Then, 1 ml of HClO₄(70%) is added to the sample solution. After concentrating the mixture to about 1 ml, 5 ml of 6 M HCl is added; all of the mixture is then heated at 97°C for 20 min. To the solution adjusted to pH 1, are added 1 ml of 0.1% DAN-0.1 M HCl, 0.5 ml of a 0.1 M EDTA-0.1 M NaF solution, and then 25 ml of water for dilution. The solution is then heated at 50°C for 20 min. The sample solution is extracted with 10 ml of cyclohexane, giving the fluorescent species. The organic phase is measured by a fluorescence spectrometer with a wavelength interval of 138 nm. The total selenium content is determined over the range of 0.151000 ng. The amounts of selenium in commercial ZnS have been determined to be 0.875 ppm (Sample 1), 1.74 ppm (Sample 2), and 0.26 ppb (Sample 3: taken 1.00 g).