Analysis of ¹⁸O/¹⁶O Isotope Ratios in Organic Matter by Laser Ablation IRMS

In recent years, the application of laser ablation isotope ratio mass spectrometry has revolutionized the field of carbon isotope analysis, enabling routine analyses at high spatial resolution (30-40 μm). Until now, an equivalent analytical method for oxygen isotope ratio (¹⁸O/¹⁶O) measurements has been lacking. In this article, we describe a preparatory system for analysis of the oxygen isotope composition of carbon monoxide produced from organic samples. The system couples a UV laser platform and automated cryofocusing unit with an isotope ratio mass spectrometer. The method is tested on cellulose and wood (tree rings) and is shown to produce data with analytical precision typically better than 0.4‰ with a sampling resolution of 100 μm (laser beam diameter). Coupled with spatially accurate and minimally invasive laser sampling, the ability to measure stable oxygen isotopes in this way represents a significant advance as it opens up new research opportunities in plant sciences, ecology, paleoclimatology, and science-based archeology.