High-Precision Oxygen-Isotope Analysis of Iron (Oxyhydr)oxides Using High-Temperature Conversion Isotope Ratio Mass Spectrometry.

We introduce a novel high-precision method for oxygen-isotope analysis of iron (oxyhydr)oxides using high-temperature conversion isotope ratio mass spectrometry (HTC-IRMS). In this approach, a finely ground mixture of iron (oxyhydr)oxide and graphite is heated at 1450 °C in a helium flow environment, converting oxygen to CO gas with nearly 100% yield. Continuous-flow IRMS analysis of the liberated CO yields a precision of ±0.15‰ (1σ, = 28) and shows excellent agreement with (and improved precision over) traditional fluorination methods. This practical and safe technique expands access to oxygen-isotope measurements of iron oxides, thereby enhancing their utility in Earth and environmental sciences.