open access

https://hdl.handle.net/2115/97804

Oxygen Isotope Analysis for Silicate Minerals Using a High-Temperature Conversion/Elemental Analyzer-Isotope Ratio Mass Spectrometer

英語

thermal conversion

2025-09-15

John Wiley & Sons

Rapid communications in mass spectrometry

39(17)

e10072

Rationale : Oxygen isotope composition of silicates is an important indicator of the formation environment and/or subsequent geochemical processes of minerals. Compared to carbonate minerals and organic matter, silicate is a less common target for oxygen isotope measurements because of the need for specialized fluorination instruments to break strong Si–O bonds. Methods : We introduce a simple method using a high-temperature conversion elemental analyzer-isotope ratio mass spectrometer (TC/EA-IRMS), which does not require specialized instrumentation. Silicate powder with various fluorine compounds and ratios of fluorine/oxygen were decomposed at 1450°C, and then, mass spectral characteristics, oxygen yields, and δ18O values were compared. Results : NaF and KF were the most reactive fluorine sources, followed by polytetrafluoroethylene, LiF, CaF2, BaF2, and AlF3, with decreasing reactivity. The F/O ratio affected the tailing of the CO peaks in the mass spectrum. Higher F/O ratios show a more rapid regression to background, resulting in higher reproducibility of oxygen yield and δ18O. In addition to simply adding fluorides to the sample, homogenization treatment also improved the reactivity. Activated carbon catalyzed by nickel is a better carbon source than graphite in terms of reactivity. The quartz and smectite with NaF added at an F/O ratio of 6 provided 90.0%–99.3% of oxygen yields, δ18O values that deviated less than 1.42‰ from literature values, and 0.18‰–0.30‰ of precision. Conclusions : Although further investigation is required to verify its accuracy, the potential of the TC/EA-IRMS method for silicates is demonstrated. Because the hydrogen isotope composition can also be examined using the same instrument, it is expected that this method can be applied to a wider range of earth materials, including hydrous silicates such as clay minerals.

学術雑誌論文

Accepted Manuscript

This is the peer reviewed version of the following article: Kikuchi, R., Ishiwata, T. and Tayasu, I. (2025), Oxygen Isotope Analysis for Silicate Minerals Using a High-Temperature Conversion/Elemental Analyzer-Isotope Ratio Mass Spectrometer. Rapid Commun Mass Spectrom, 39: e10072, which has been published in final form at https://doi.org/10.1002/rcm.10072. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

0951-4198