> I would like to know what grade of CO2 people use when
> equilibrating waters
> for subsequent delta 18O analysis on a mass spec.

Our system (Finnigan GasbenchII) is running with CO2 4.5 (99.995) as
standard gas and a mix of He(5.0) + 0.5%CO2(4.5) for equilibration.

regards,
Robert

--
Robert van Geldern
Leibniz Institute for Applied Geosciences (GGA)
S3: Geochronology and Isotopehydrology
Stilleweg 2, 30655 Hannover, Germany
phone: +49-(0)511-643-2313 (office), -2539 (lab)
fax: +49-(0)511-643-3665
mailto:[log in to unmask]