Why don't you buy some high grade CO without a known isotopic composition and then calibrate it against known standards such as carbonate? For our measurements, we run two different isotopic standards with each batch of samples and don't bother to calibrate the reference gas. 

Anthony

--- You wrote:
Dear all,

I'm having very big problems in finding suppliers of CO with d18O and d13C
determined, in small cylinders (1L) to use in dual inlet systems.
Some of the suppliers cannot send over-ocean (OzTech in USA nor from
Mexico). Others apparently don't have the gas anymore in catalogue (Messer
Grisheim, in Italy at least: Messer Germany did not yet reply me).

So: anyone could help me?

Thank you!!

----------------------------------
Giovanni Calderone, PhD
EC-Joint Research Centre
Institute for Health & Consumer Protection Physical and Chemical Exposure
Unit - BEVABS
TP740 via Fermi, 2 21020 ISPRA Italy
Tel. Off.: +(39) 0332 78 5668
Tel. Lab.: +(39) 0332 78 5258
Fax: +(39) 0332 78 9303
http://ihcp.jrc.it/
http://hosting.jrc.cec.eu.int/pce/
e-mail: [log in to unmask]
--- end of quote ---