Iron Isotopic Measurement using Large-Geometry High-Resolution Multi-Collector Inductively Coupled Plasma Mass Spectrometer

High-precision and accurate Fe isotopic analyses are essential for various geological processes. In this study, Fe isotopic measurements were optimized on a large-geometry, high-resolution Nu Plasma 1700 MC-ICP-MS instrument, which can distinguish Ar-related interferences completely as opposed to other general-sized MC-ICP-MS instruments. Under the conditions of high mass resolution, complete separation of Ar-related interference can be achieved. We evaluated the type and intensity of all Ar-related interferences. The effects of the acid molarity, concentration mismatch, residual HCl, and matrix elements were also evaluated. The results demonstrate that the molarity of the acid, residual HCl, and Cr significantly affected the precision of the Fe isotopic measurements. Fe was purified by one-step column anion-exchange separation using the anion resin AG-MP-1M. The long-term external precisions of delta Fe-56 and delta Fe-57 were greater than +/- 0.03 parts per thousand (2SD) and +/- 0.06 parts per thousand (2SD), respectively. The Fe isotopic compositions of the five geological reference materials measured in this study agreed with previously published data, within uncertainties.