Dear All, does anyone know a supplier for CH4 gas with a certified delta 13C value at natural abundance (around -45 permil) and/or enriched with a few hundred permil? I tried Messer Griesheim, but they don't have it. Are there more people working on determining delta 13C from CH4, either from emissions or air? It would be interesting to share some experiences. Thanks! @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ Richard van Logtestijn Vrije Universiteit Faculty Biology Department of Systems Ecology De Boelelaan 1087 1081 HV Amsterdam the Netherlands tel +31 20 4447247 fax +31 20 4447123 e-mail : [log in to unmask] @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@