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Updated: Oct 26, 2026

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Published on: August 31, 2017
Long-Term Performance and Bulk-Isotope Effects in Methane Clumped-Isotope Measurements Using a 253 Ultra HR-IRMS
Naizhong Zhang1,2, Alexis Gilbert3, Mayuko Nakagawa1
1Department of Earth and Planetary Sciences, Institute of Science Tokyo, Tokyo, Japan.
Rationale:
Changes in instrument condition over time may affect methane clumped-isotope measurements, requiring long-term monitoring of calibration performance. Whether the 253 Ultra calibration framework remains valid over multiyear operation and applicable across natural bulk-isotope compositions, particularly to low-δD methane with weak 12CH2D2 signals, has not been systematically evaluated.
Methods:
Long-term performance of the Science Tokyo 253 Ultra was evaluated from 2019 to 2026 using reference-gas zero tests, repeated working-gas measurements, and independently prepared equilibrated methane gases. Equilibrated gases with different δ13C and δD compositions were used to test for possible bulk-isotope dependence in Δ13CH₃D and Δ12CH2D2 measurements. External consistency was assessed using nine shared methane gases measured across seven laboratories with 253 Ultra HR-IRMS, Panorama HR-IRMS, and mid-infrared laser spectroscopy.
Results:
Reference and working gases showed no temporal drift, and equilibrated gases measured from 2021 to 2026 remained consistent with the calibration framework established in 2020. No systematic dependence of Δ13CH₃D or Δ12CH2D2 on either δ13C or δD was resolved, including for equilibrium gases with δD values as low as -335‰. Science Tokyo measurements were generally consistent with results from other laboratories across a wide range of bulk-isotope compositions and nonequilibrium clumped-isotope signatures.
Conclusions:
The calibration framework established for methane clumped-isotope measurements with the Science Tokyo 253 Ultra HR-IRMS remained stable and applicable over multiple analytical campaigns. Validation measurements and interlaboratory comparisons demonstrated consistent results across a broad range of methane bulk-isotope compositions, without the need for campaign-specific or additional bulk-isotope-dependent corrections, with δD values extending down to -335‰.
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