Xinyu Xia Zhisheng Li Dennis D. Coleman Robert F. Dias Ling Gao Jian Li Andrei Deev Jin Li Daniel Dessort Dominique Duclerc Liwu Li Jinzhong Liu Stefan Schloemer Wenlong Zhang Yunyan Ni Guoyi Hu Xiaobo Wang Yongchun Tang Jinxing Dai 2012 Compound-specific carbon and hydrogen isotopic compositions of three natural gas round robins were calibrated by ten laboratories carrying out more than 800 measurements including both on-line and off-line methods. Two-point calibrations were performed with international measurement standards for hydrogen isotope ratios (VSMOW and SLAP) and carbon isotope ratios (NBS 19 and L-SVEC CO₂). The consensus δ¹³C values and uncertainties were derived from the Maximum Likelihood Estimation (MLE) based on off-line measurements; the consensus δ²H values and uncertainties were derived from MLE of both off-line and on-line measurements, taking the bias of on-line measurements into account. The calibrated consensus values in ‰ relative to VSMOW and VPDB are: NG1 (coal-related gas): Methane: δ²H_VSMOW = − 185.1‰ ± 1.2‰, δ¹³C_VPDB = − 34.18‰ ± 0.10‰ Ethane: δ²H_VSMOW = − 156.3‰ ± 1.8‰, δ¹³C_VPDB = − 24.66‰ ± 0.11‰ Propane: δ²H_VSMOW = − 143.6‰ ± 3.3‰, δ¹³C_VPDB = − 22.21‰ ± 0.11‰ i-Butane: δ¹³C_VPDB = − 21.62‰ ± 0.12‰ n-Butane: δ¹³C_VPDB = − 21.74‰ ± 0.13‰ CO2: δ¹³C_VPDB = − 5.00‰ ± 0.12‰ NG2 (biogas): Methane: δ²H_VSMOW = − 237.0‰ ± 1.2‰, δ¹³C_VPDB = − 68.89‰ ± 0.12‰ NG3 (oil-related gas): Methane: δ²H_VSMOW = − 167.6‰ ± 1.0‰, δ¹³C_VPDB = − 43.61‰ ± 0.09‰ Ethane: δ²H_VSMOW = − 164.1‰ ± 2.4‰, δ¹³C_VPDB = − 40.24‰ ± 0.10‰ Propane: δ²H_VSMOW = − 138.4‰ ± 3.0‰, δ¹³C_VPDB = − 33.79‰ ± 0.09‰ All of the assigned values are traceable to the international carbon isotope standard of VPDB and hydrogen isotope standard of VSMOW. application/pdf 10.1016/j.chemgeo.2012.03.008 en Elsevier Inter-laboratory calibration of natural gas round robins for δ²H and δ¹³C using off-line and on-line techniques article