New Potential Haematite and Magnetite Reference Materials for Iron Isotope Measurements by Solution Nebulisation MC ‐ ICP ‐ MS and by In Situ ns ‐ LA ‐ MC ‐ ICP ‐ MS

Iron isotope ratios of haematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) provide insights into geochemical, environmental and planetary processes. In most studies, Fe isotope measurements are commonly performed using solution nebulisation multi‐collector inductively coupled plasma‐mass spectrometry (SN‐MC‐ICP‐MS). Nanosecond laser ablation multi‐collector inductively coupled plasma‐mass spectrometry ( ns ‐LA‐MC‐ICP‐MS) requires minimal sample preparation, and provides spatially resolved variation of iron isotopes at micro‐scale. However, homogeneous and matrix‐matched haematite/magnetite reference materials are lacking for precise in situ isotopic measurement. The iron isotope ratios of two potential reference materials resembling natural haematite (HMIE‐NP‐B01) and natural magnetite (MAKP‐NP‐B01) were characterised. Size fractions between 5–63 μm of the powdered Fe oxides were milled to nanoparticles, freeze‐dried, homogenised, and pressed into pellets. The materials were then evaluated using SN‐MC‐ICP‐MS and LA‐MC‐ICP‐MS. Sample powders of the two materials were measured by SN‐MC‐ICPMS after sample digestion and column separation and pressed pellets were analysed directly via ns ‐LA‐MC‐ICP‐MS. In both cases iron isotope delta values are reported relative to the certified reference material IRMM‐014, used as the bracketing standard (calibrator). The solution measurements yielded δ 56 Fe values of ‐0.25 ± 0.08‰ ( N = 13, 2 s ) for HMIE‐NP‐B01, and ‐0.05 ± 0.09‰ ( N = 12, 2 s ) for MAKP‐NP‐B01, considered as the preferred Fe isotope delta values. In situ isotopic analysis via ns ‐LA‐MC‐ICP‐MS yielded δ 56 Fe values of ‐0.28 ± 0.28‰ ( N = 19, 2 s ) for HMIE‐NP‐B01 and ‐0.12 ± 0.24‰ ( N = 22, 2 s ) for MAKP‐NP‐B01, consistent with the solution Fe isotope data. The homogeneity of Fe isotopes of the pellets was evaluated by ns ‐LA‐MC‐ICP‐MS analyses of three different positions to further confirm that both materials are isotopically homogeneous. Both materials can be considered as potential quality control and bracketing reference materials for Fe isotopic measurements by in situ ns ‐LA‐MC‐ICP‐MS analysis.