A robust method for direct calibration of isotope ratios in gases against liquid/solid reference materials, including a laboratory comparison for δ13C‐CH4. (20th November 2020) - Sperlich, Peter; Moossen, Heiko; Geilmann, Heike; Bury, Sarah J.; Brown, Julie C.S.; Moss, Rowena C.; Brailsford, Gordon W.; Brand, Willi A.