There is an extensive discussion of this separation issue in several older papers and especially in Farquahar et al 1997.
One way we have found to get around this problem is to work with an Elemental Analyser separating gases with a "purge and trap" system rather than a GC column. You can find a discussion comparing both techniques in Fourel et al RCM 2011.
If you want to discuss it in greater detail or send some test samples please do not hesitate to contact me off the list.
Dr François FOUREL
UMR CNRS 5023 LEHNA
Université Claude Bernard Lyon 1
3 rue Raphaël Dubois - Bât. Forel
F-69622 VILLEURBANNE Cedex - FRANCE
Tél : +33 (0) 4 72 43 16 81
Email : [log in to unmask]