Determination of selenium at trace levels in geologic materials by energy-dispersive X-ray fluorescence spectrometry

Abstract

Low levels of selenium (0.1–500 ppm) in both organic and inorganic geologic materials can be semiquantitatively measured by isolating Se as a thin film for presentation to an energy-dispersive X-ray fluorescence spectrometer. Suitably pulverized samples are first digested by fusing with a mixture of Na 2CO 3 and Na 2O 2. The fusion cake is dissolved in distilled water, buffered with NH 4Cl, and filtered to remove Si and the R 2O 3 group. A carrier solution of Na 2TeO 4, plus solid KI, hydrazine sulfate and Na 2SO 3, is added to the filtrate. The solution is then vacuum-filtered through a 0.45-μm pore-size filter disc. The filter, with the thin film of precipitate, is supported between two sheets of Mylar® film for analysis. Good agreement is shown between data reported in this study and literature values reported by epithermal neutron-activation analysis and spectrofluorimetry. The method can be made quantitative by utilizing a secondary precipitation to assure complete recovery of the Se. The X-ray method offers fast turn-around time and a reasonably high production rate.