Determination of selenium and arsenic in plant and animal tissues by hydride generation inductively coupled plasma mass spectrometry

Abstract

A method for determining Se and As in plant and animal tissues by hydride generation inductively coupled plasma mass spectrometry was developed, based on an evaluation of sample digestion, chemical interference and isobaric interference. Plant or animal tissue samples were digested with HNO₃+ HCIO₄. Se^VI was reduced to Se^IV by heating the samples in 4 mol l^–1 HCI, but As remained as As^V. Digestion with HNO₃+ HClO₄ was superior to digestion with HNO₃+ H₂O₂, because the former was efficient, complete, and had less isobaric interference from bromine. The observed chemical interference might be caused by Cu in animal tissues forming precipitates with the hydrides during hydride generation. This chemical interference was removed by raising the sample acidity to 4 mol l^–1 HCl. The isobaric interference of ⁸¹BrH with ⁸²Se was removed by evaporating the samples at 200 °C and by isobaric correction. Se could be measured by using ⁷⁷Se, ⁷⁸Se or ⁸²Se. The limit of detection was about 0.02 µg l^–1 for both Se and As, which is less than the background equivalent concentration of 0.05 µg l^–1 for Se and As. Based on a dilution factor of 50, the limit of detection for both Se and As in tissue samples was 0.001 mg kg^–1(0.001 ppm). The measured Se and As contents in five NIST SRMs were in good agreement with the certified values.