Absolute measurements and certified reference material for iron isotopes using multiple-collector inductively coupled mass spectrometry

Two enriched isotopes, 99.94 at.% Fe-56 and 99.90 at.% Fe-34, were blended under gravimetric control to prepare ten synthetic isotope samples whose Fe-56 isotope abundances ranged from 95% to 20%. For multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) measurements typical polyatomic interferences were removed by using Ar and H-2 as collision gas and operating the MC-ICP-MS system in soft mode. Thus high-precision measurements of the Fe isotope abundance ratios were accomplished. Based on the measurement of the synthetic isotope abundance ratios by MC-ICP-MS, the correction factor for mass discrimination was calculated and the results were in agreement with results from IRMM014. The precision of all ten correction factors was 0.044%, indicating a good linearity of the MC-ICP-MS method for different isotope abundance ratio values. An isotopic reference material was certified under the same conditions as the instrument was calibrated. The uncertainties of ten correction factors K were calculated and the final extended uncertainties of the isotopic certified Fe reference material were 5.8363(37) at.% Fe-54, 91.7621(51) at.% Fe-56, 2.1219(23) at.% Fe-57, and 0.2797(32) at.% Fe-58. Copyright (C) 2008 John Wiley & Sons, Ltd.