An improved system and analytical method for determining oxygen isotopes in ¹⁸O-enriched water samples

The spatiotemporal differences in the hydrogen and oxygen isotopic composition of water offer a powerful technical approach for research on the water cycle, paleoclimate reconstruction, and water source identification. Hydrogen and oxygen isotopes in certain specialized samples, such as ¹⁸O-enriched water, have been utilized in food science, environmental ecology, and medical research. To address the low efficiency of traditional offline H₂O-CO₂ equilibrium methods and the pronounced memory effect associated with continuous-flow techniques for ¹⁸O-enriched water samples, we propose a novel analytical system and methodology for oxygen isotope determination in water. The system was independently designed and established in-house. A water equilibrium unit and an extraction preparation unit were organically combined in this system. A water bath shaker was designed for the equilibrium system to accelerate the complete equilibrium exchange and reduce reaction time. A 3.0 mL water sample was injected into a glass bottle and equilibrated with carbon dioxide gas in a water bath at 25 °C for 4 h. While maintaining a high analytical accuracy (within 0.10% and 0.50% for reference materials USGS45 and IAEA-608, respectively), this method significantly improves the efficiency, reducing the processing time by over 10 h. It offers a preferred solution for oxygen isotope analysis in water samples, particularly those enriched in ¹⁸O.