A robust method for direct calibration of isotope ratios in gases against liquid/solid reference materials, including a laboratory comparison for δ13C-CH4.

Our Gas/EA/IRMS technique might close this calibration gap, as it can be adapted to calibrate isotope ratios in non-CH 4 gases to available liquid/solid RMs. LETTER TO THE EDITOR Arobustmethodfordirectcalibrationofisotoperatiosin gasesagainstliquid/solidreferencematerials,includinga laboratorycomparisonfor 13 C-CH 4 Although stable carbon isotope ratios in atmospheric methane (CH 4) are frequently used to constrain biogeochemical processes responsible for the increase of this powerful greenhouse gas, 1-3 certified reference materials (RMs) for isotope ratios in CH 4 have been lacking for decades. Our Gas/EA/IRMS systems enable adherence to the PIT for the measurements of gaseous/liquid/solid samples, which is critical for the calibration of isotope ratios in gases against liquid/solid RMs with high accuracy. A robust method for direct calibration of isotope ratios in gases against liquid/solid reference materials, including a laboratory comparison for ¹³C-CH₄. [Extracted from the article]