Determination of titanium isotopes in rutiles with high spatial resolution by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry

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Crystallization of Fe–Ti oxides can induce significant Titanium (Ti) isotope fractionation during magmatic differentiation. As such, rutile (TiO2), a common Ti-rich mineral present in igneous, metamorphic, and sedimentary rocks, can serve as a tracer of the geologic processes. A new method to determine the Ti mass-dependent isotope fractionation of rutiles with high precision and high spatial resolution was developed using femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). A high sensitivity cone combination (Standard sampler cone + X skimmer cone) can increase the Ti signals, which permits ablation of rutiles with a low ablation frequency of 1 Hz and analysis with high spatial resolution. However, a signal smoothing device is necessary to overcome the signal fluctuation issue that commonly occurs in the modern low-dispersion ablation cell at a low ablation frequency. Our results show that changing laser parameters (spot size and laser fluence) or signal mismatch between samples and references would bias toward higher δ49Ti values (0.16‰ to 0.59‰) in dry plasma, which can be suppressed by using wet plasma conditions instead. After these optimizations, the spatial resolution of our method at horizontal- and vertical-axis can be promoted to 10 μm and ≈4 μm, respectively, meanwhile ensuring accurate δ49Ti results with a precision of ±0.10‰. The long-term measurements of a rutile USA75 by fs-LA-MC-ICP-MS show a good reproducibility of δ49Ti (±0.11‰). Measurements of 9 natural rutile crystals by both solution MC-ICP-MS and fs-LA-MC-ICP-MS provide consistent δ49Ti values, confirming the robustness of our fs-LA-MC-ICP-MS method. A significant variation of δ49Ti (up to ≈2.94‰) among the 12 rutiles was observed, indicating that Ti isotopes in rutiles can be a useful geochemical tracer. Four rutile crystals (e.g., USA75, Bra12, Sco2 and Bra6) are shown to be homogeneous in δ49Ti within an uncertainty of <0.13‰ and can therefore serve as reference materials for future in situ Ti isotope ratios measurement.

Original languageEnglish
Article number106646
JournalSpectrochimica Acta - Part B Atomic Spectroscopy
Number of pages10
Publication statusPublished - 2023

Bibliographical note

Publisher Copyright:
© 2023

    Research areas

  • fs-LA-MC-ICP-MS, High spatial resolution, Microanalysis, Rutile, Ti isotopes

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