Iron isotope ratios of hematite and magnetite, two Fe-rich minerals commonly found in various rocks and mineral deposits, have frequently been analyzed to understand ore-forming processes in iron deposits.   Using the high spatial resolution of laser ablation multicollector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS), informations about the temporal evolution of mineral formation in hematite and magnetite can be explored. However, the limited commercial availability of hematite and magnetite reference materials complicates LA-MC-ICP-MS measurements. Suitable matrix matched reference materials are crucial to validate in situ Fe isotope data to overcome matrix effects during measurements.  

In this study, the iron isotope ratios of one hematite sample (HMIE-NP-B01) and one magnetite sample (MAKP-NP-B01) were evaluated using both solution nebulization MC-ICP-MS and ns-LA-MC-ICP-MS. Instrumental mass bias caused by mass discrimination was corrected through a combination of internal correction, using Ni as an internal standard (from the nebulized standard solution), and external standard-sample bracketing correction. For solution isotopic analysis, following sample digestion and chromatographic Fe isolation, the δ⁵⁶Fe values were found to be -0.23 ± 0.12‰ (n=13) for HMIE-NP-B01 and -0.05 ± 0.12‰ (n=11) for MAKP-NP-B01 (2SD, calculated as the mean of 3-6 replicates from different measurement sessions). In situ isotopic analysis via ns-LA-MC-ICP-MS yielded δ⁵⁶Fe values (2SD, IRMM-014) between -0.28 ± 0.14‰ (n=19) for HMIE-NP-B01 and -0.12 ± 0.12‰ (n=22) for MAKP-NP-B01, based on ablation over 200 cycles with an integration time of 0.524s. Furthermore, homogeneity tests conducted using LA-MC-ICP-MS showed that the δ⁵⁶Fe values are consistent with the solution results. Overall, the results from ns-LA-MC-ICP-MS closely matched those from solution MC-ICP-MS, demonstrating strong agreement between the two methods.