A determination method for isotope ratios of iron in faeces samples is studied in this paper. The sample is decomposed in microwave oven by HNO3. A double focusing ICP-MS mass spectrometer (ELEMENT) working at resolution of 3000 allows the complete resolution of polyatomic ions overlapping. Instrumental parameters of the mass spectrometer are optimized for optimum precision. The RSD values obtained for the isotope ratios of 54Fe/56Fe, 57Fe/56Fe and 58Fe/56Fe are 0.23, 0.14, 0.22%, respectively, for a natural standard solution of 5ug/ml. The method has been used to iron nutrition studies.
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