Calibration of an optical methane clumped isotope thermometer
crossref(2023)
摘要
<p>Methane clumped isotope thermometry relies on accurate measurements of relative abundances of the doubly-substituted isotopologues <sup>12</sup>CH<sub>2</sub>D<sub>2</sub> and <sup>13</sup>CH<sub>3</sub>D. Calibration of the thermometer requires, regardless of the applied technique, i.e., laser absorption spectroscopy or high-resolution mass spectrometry, routine preparation of thermally re-equilibrated samples spanning the temperature and bulk isotopic composition (δ<sup>13</sup>C-, δD-CH<sub>4</sub>) range of the target applications.</p> <p>Here we present a practical method for methane isotopologue re-equilibration over activated γ-Al<sub>2</sub>O<sub>3</sub>. We demonstrate complete and reproducible re-equilibration of clumped isotope signatures with minimal alteration of the bulk isotope composition, almost complete sample recovery, and no detectable formation of decomposition products. Samples spanning a range in δD-CH<sub>4 </sub>of 100 ‰ were equilibrated between 100 °C and 500 °C and used to calibrate a high-resolution quantum cascade laser absorption spectrometer. In addition, we report on a comparison between the spectroscopic measurements carried out at Empa and an independently calibrated high-resolution mass spectrometric technique using a Thermo MAT253 Ultra at IMAU, Utrecht University.</p> <p><em>This study is supported by the European Commission under the Horizon 2020 – Research and Innovation Framework Programme, H2020-INFRAIA-2020-1 (grant no. 101008004) and the Swiss National Science Foundation project no. 200021_200977.</em></p>
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