Work

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

Year: 2025

Type: article

Abstract: ABSTRACT 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 δ 18 O values were compared. Results NaF and KF were the most reactive fluorine sources, followed by polytetrafluoroethylene, LiF, CaF 2 , BaF 2 , and AlF 3, 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 δ 18 O. 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, δ 18 O 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.

Source: Rapid Communications in Mass Spectrometry

DOI: 10.1002/rcm.10072

Authors: Ryosuke Kikuchi, Tobimaru Ishiwata, Ichiro Tayasu

Institutions: Hokkaido University, Research Institute for Humanity and Nature

Language: English

Topic: Geological and Geochemical Analysis

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: bronze

Funders: Research Institute for Humanity and Nature, Japan Society for the Promotion of Science

Award: Understanding biosphere-hydrosphere-atmosphere-lithosphere interactions 3.2 billion years ago with an international continental drilling program