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.采用铂催化CO₂-O₂交换法（platinum catalysed CO₂-O₂ exchange method）开展CO₂中三重氧同位素（triple oxygen isotope, Δ’17O）测量时，需精准测定氧同位素交换分馏因子（oxygen isotope exchange fractionation factors）与指数项。 该类催化交换分馏因子通常在高温（约750℃）下测定。然而已有研究报道该类因子存在显著的实验室间不一致性，其主要归因于交换反应器延伸至加热区外的部分所产生的热梯度诱导分馏。 本研究采用可有效消除热梯度的新型实验装置，对上述分馏因子与指数项进行了实验测定，所得结果与理论平衡值吻合良好。 研究结果证实，交换分馏因子的理论-实验偏差由热梯度主导，并揭示了该类因子与交换反应器位于加热器内的区段之间存在稳健的指数相关性。 我们提出了一套用于分馏因子标准化的全新框架，该框架对实现精准且符合实验室间一致性的CO₂中Δ’17O测量至关重要。