Nick Ostle wrote:

> ISOGEOCHEMISTS,
>
> The research that I am involved in requires the use of both  C and O
> enriched isotopes in the same tracer studies and I need to be sure
> that I can correctly attribute values to 13C/12C and 18O/16O in CO2.
> Manufacturers suggest that their instruments can do this by using the
> mz 46/44 ratio. However when both C and O of CO2 are enriched this is
> not always possible as the Craig 18O correction is designed for
> near-natural abundance levels. Any ideas?
>
> nick
>
>                      Nick Ostle
>       Institute of Terrestrial Ecology
>                 ITE- Merlewood
>              Grange-Over-Sands
>               Cumbria, LA11 6JU
>                      England
>
>            e-mail: [log in to unmask]
>         tel: ++44 (0)15395 32264
>         fax: ++44(0)015395 34705

Here is a crazy idea.  How about equilibrating the Carbon dioxide with a
small amount of water and then measuring the oxygen isotope ratios of the
water from that you can derive the delta-o18 of the carbon dioxide. ....
it might work.  Leo.