A comprehensive study of the CO2-O2 isotope exchange technique to standardize triple oxygen measurements in CO2

Triple oxygen isotope (Δ’17O) measurements in CO2 using the platinum catalysed CO2-O2 exchange method require precise determination of the oxygen isotope exchange fractionation factors and exponent. These catalysed exchange fractionation factors are typically determined at elevated temperature (~750 oC). However, large inter-laboratory inconsistencies have been reported in these factors, primarily attributed to thermal-gradient-induced fractionation arising from portions of the exchange reactor extending beyond the heated zone. This study experimentally determines these fractionation factors and exponent using a novel setup that effectively eliminated thermal gradient and yielded results in good agreement with the theoretical equilibrium values. These results establish that the theory-experimental discrepancies in exchange fractionation factors are driven by thermal gradient and reveal a robust exponential correlation between these factors and the portions of the exchange reactor lying within the heater. We propose a new framework to standardize fractionation factors, which is crucial for accurate and interlaboratory-consistent Δ’17O measurements in CO2.