High Spatial Resolution In Situ Fe Isotope Analysis by Laser Ablation Collision/Reaction Cell MC-ICP–MS: Application to Chang’e-6 Lunar Samples

Iron (Fe) isotopes act as a powerful tracer in geological processes for analyzing terrestrial and extraterrestrial materials. Laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP–MS) is widely used for in situ Fe isotope analysis. However, its application is limited by argon (Ar)-based polyatomic isobaric interference and reduced sensitivity under high mass resolution, restricting investigations of intragrain variability and fine-grained extraterrestrial samples. Herein, the first femtosecond LA collision/reaction cell (CRC) MC-ICP–MS analysis for high spatial resolution of Fe isotope is reported. A hydrogen (H 2 )–helium (He) gas mixture in the CRC effectively suppressed Ar-based interferences, enabling accurate analysis of Fe isotopes in a low-resolution mode. Substitution of the conventional ultraviolet laser with a 1028 nm infrared laser significantly enhanced ablation rates, without compromising the stability of Fe isotope ratios. Optimization of the analytical conditions increased Fe isotope sensitivity by >50-fold than conventional LA-MC-ICP–MS, providing a strong foundation for high spatial resolution analysis. Replicated analyses were performed on six Fe-bearing materials (magnetite, ilmenite, pyrite, chalcopyrite, olivine and basalt glass) using the as-developed method with small beam spots of 8–15 μm in a single-spot mode. The measured δ 56 Fe IRMM-014 values are consistent with reference values, with an external reproducibility of 0.09‰–0.15‰ (2SD). Compared with traditional Fe isotope microanalysis techniques, the proposed method improves spatial resolution of the analytical area by 1–2 orders of magnitude. The method was further applied to impact glass, ilmenite, and olivine samples collected by China’s Chang’e-6 lunar missions, revealing significant intraparticle Fe isotope variability at micrometer scales, indicating the capability of LA-CRC-MC-ICP–MS to resolve Fe isotope heterogeneity in fine-grained samples with complex compositions. Thus, our method highlights its potential for high spatial resolution of isotopes in planetary samples.