Evaluation of digestion procedures for the determination of selenium in soil comparing vapour generation and graphite furnace atomic absorption spectrometry with Zeeman-effect background correction

Abstract

In this work, three mixed acid digestion methods, HNO₃-HClO₄-HF, HNO₃-H₂O₂-HF and HNO₃-HCl-HF, have been studied. The digest solutions were analysed for selenium by graphite furnace atomic absorption spectrometry (GFAAS) using either deuterium or Zeeman-effect background correction systems and by vapour generation atomic absorption spectrometry (VGAAS). Because soil samples contain substantial amounts of iron and phosphorus, the accurate determination of selenium by deuterium are background corrected GFAAS is complicated by the well documented spectral interferences which give rise to over-correction. However, this over-correction can be simply eliminated by the use of Zeeman-effect background corrected GFAAS. The accuracy of the methods was assessed by the use of the NIST Standard Reference Material (SRM) Coal Fly Ash 1633A. The precision of the measurements (RSD) ranges from 3.8 to 9.9% with Zeeman-effect GFAAS, and from 0.2 to 1.5% with VGAAS, for selenium concentrations of up to 20 ng ml^–1. The three digestion methods give comparable results on both Zeeman-effect GFAAS and VGAAS. However, the HNO₃-H₂O₂-HF and HNO₃-HCl-HF procedures are preferred because they are simple and less time consuming.