compounds (CO2, CaCO3) enriched in O-18 are usually enriched in O-17 as
well. This may affect significantly the 45/44 measurement. In order to make
the right corrections, you need to measure the ratio 47/44 as well, which
may be possible for O-18/C-13 enriched compounds.
In addition, if CO2 enriched in O-18, O-17 and C-13 is mixed with CO2 with
natural isotope abundance, the mixture is not in isotopic equilibrium (the
abundance of isotopic species does not obey the statistical distribution)
and corrections may become impossible without previous re-equilibration
with a catalyst.
You may find detailed information in:
R. Gonfiantini, S. Valkiers, P. Taylor, P. De Bievre: Using isotopic
disequilibtrium of CO2 to model gas adsorption in mass spectrometric
measurements. Int. J. of Mass Spectrometry and Ion Processes, vol. 161,
pag. 15-26 (1997).
At 11:34 05/08/99 +0100, you wrote:
>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 Ostle
> Institute of Terrestrial Ecology
> ITE- Merlewood
> Cumbria, LA11 6JU
> e-mail: [log in to unmask]
> tel: ++44 (0)15395 32264
> fax: ++44(0)015395 34705
Prof. Roberto Gonfiantini
Please note the new address:
Istituto di Geocronologia e Geochimica Isotopica del CNR
Area della Ricerca di Pisa
Via V. Alfieri, 1
Loc. San Cataldo
I-56127 Ghezzano (Pisa)
Phone +39-050-588358 (direct) - Fax +39-050-588360
E-mail [log in to unmask]