IF you can't find "light" CO2 in a bottle you could capture CO2 repired from
living organisms which should be around -24 permil and feed that into your
experiment somehow. You'd have to check the variability in 13C/12C of the
CO2. It is good pratice to measure the 13C/12C in background external CO2
anyway, so it should be feasible to monitor this.

I'm not sure of any references on this. Steve Leavitt et al. have recently
done some work using light CO2.


>Hi folks,
>                  A student here is undertaking an elevated CO2
>experiment which involves adding extra CO2 to the ambient air in a
>growth chamber. The 'tank' CO2 is at about -40 per/mil (13C) but after
>dilution by the ambient CO2 in the chamber works out to be about -12
>per mil, we are concerned that this is not different enough from
>ambient to be able to trace the path of the carbon through the
>experiment. We would like to know if there is any bottled CO2 out
>there with a more extreme signature than -40. We are reluctant to
>start using 13-C enriched CO2 for reasons of cost as the chamber is
>not sealed and gas addition is constant.  Any help would be greatly
>appreciated.
>
>                                                             Cheers,
>Darren
>
>     Stable Isotope Facility
>      ITE Merlewood
>       Grange-over-Sands
>        Cumbria,
>          UK
>
>

David A. Pepper, PhD Student
School of Biological Sciences
The University of Sydney, NSW 2006, Australia.
Phone +61 2 9351 3078, Fax +61 2 9351 4119
Email [log in to unmask]