HIGH TEMPERATURE CONVERSION–METHANATION–FLUORINATION: A NOVEL METHOD FOR HIGH-PRECISION TRIPLE OXYGEN ISOTOPE MEASUREMENTS (Invited Presentation)

In most natural systems, triple oxygen isotope anomalies (denoted Δ'¹⁷O) vary by small amounts on the order of 10s of ppm, necessitating very high-precision measurements (≤ 10 ppm 1σ) of Δ'¹⁷O to extract a clear signal. Such analytical precisions have been difficult to achieve for several materials such as organics, sulfates, and nitrates, leaving them unexplored for small Δ'¹⁷O variations. We have developed a novel method that enables high-precision measurements in a diverse range of materials including but not limited to phosphates, sulfates, organics, nitrates, carbonates, silicates, and waters. The method uses a three-step process to first convert sample oxygen to oxygen in CO via high temperature conversion (HTC; commonly referred to as TC/EA). Next, oxygen in CO is converted to oxygen in H₂O by a methanation process. Finally, the oxygen in water is converted to molecular oxygen (O₂) by fluorination and analyzed via dual-inlet isotope ratio mass spectrometry. Here we present results from Δ'¹⁷O measurements of standard reference materials of various material types (listed above), reporting analytical precisions that approach shot-noise limits (5 ppm 1σ) for all materials.