The offline extraction of nitrogen is a misery, especially at natural
abundances: you have to be careful to avoid fractionation, samples have to
be relatively large (especially a problem for plant samples), etc. Don't do
it: this is were continuous flow technology has really helped out.

Regarding trapping of CO2 from a CN analyser: you can go high tech and use a
CO2 collection system (like we do in our lab, we use a prep CN analyser to
collect CO2 for measurement in our accelerator for dating Ref: Hedges et al
1992, Radiocarbon 34:306-311), or just use a liquid N2 trap.

Best regards, GJ

Dr. Gert Jaap ("GJ") van Klinken,
Radiocarbon Accelerator Unit,
Research Laboratory for Archaeology and the History of Art,
University of Oxford
6 Keble Road, Oxford OX1 3QJ
Tel (+44) (01865) 273939   Fax (01865) 273932