Iron isotopic analyses of geological reference materials on MC-ICP-MS: proposal for a new Fe isotope standard IAEA B5

In recent years, iron isotopes have found increasing applications across various fields of Earth Science, including cosmochemistry, geochemistry, and environmental sciences. Isotopic reference materials play a crucial role in advancing and refining non-traditional stable isotope systematics, ensuring accurate and precise isotope ratio analyses. Consequently, the direct comparison of data obtained from different laboratories is an essential prerequisite for developing reliable systematics In the framework of the project “TEOREM - Deciphering Geological Processes using Terrestrial and Extraterrestrial ORE Minerals” (PRIN-MUR 2017AK8C32) and the project ITINERIS ISOTOPE VRE (IR0000032; PNRR; Next Generation EU), we developed the methodology for the Fe separation from different matrices, and the determination of Fe isotope ratios using High Resolution Multi-Collector Inductively Coupled Plasma Mass Spectrometer (HR-MC-ICPMS). We investigated the iron isotopic composition of a new potential iron isotope reference material, IAEA-B5. Additionally, high-precision stable Fe isotope data for widely used international reference materials (JB-2, BHVO-2, BE-N, AGV-1, and RGM-1) were obtained using a HR-MC-ICPMS Neptune Plus at the Radiogenic and Unconventional Stable Isotopes Laboratory of IGG-CNR (Pisa, Italy). The data obtained for selected igneous reference materials, ranging from basalts to andesite and rhyolite, show strong agreement with previously published values and remain within the stated analytical uncertainties. The newly certified iron isotope composition values for the IAEA-B5 standard, determined in our laboratory, are δ56Fe = 0.105 ± 0.061 (2SD) and δ57Fe = 0.147 ± 0.071 (2SD). These values are consistent with the averages of other basaltic reference materials.