Dear Karen,
We use industrial grade CO2 (very cheap) for our water
equilibration with CO2 using a multiprep and prism II.  I also
initially thought that better CO2 was necessary but was told but
someone (Matt Emmon formerly with VG, I think) to just use plain
CO2.  We have never had any problems in many years.

For reference gas we either use homemade CO2 from carrera marble
(for deltas close to zero) or 99.99% (HP) for more negative stuff.
 We can get HP CO2 with d13C of about -5 and d18O of about -12
fairly consistently from our supplier.
Jason


On Mon Apr 18 00:26:33 EDT 2005, Karen Leslie
<[log in to unmask]> wrote:

> Dear all,
>
> Many thanks to everyone who replied to my previous queries.
>
> I would like to know what grade of CO2 people use when
> equilibrating waters
> for subsequent delta 18O analysis on a mass spec. I assume that
> the purer
> the CO2 the better as impurities have the potential to be a
> source of
> contamination? The system is currently running with Scientific
> grade but is
> this necessary? Will UHP CO2 be just as good?
>
> Also, what are people using as reference gas? Is this the same
> CO2 as used
> for the equilibration or something different, say gas of a
> special or
> specific composition? This is for both waters and carbonates.
>
> Many thanks in advance,
> Karen
>
>
> Dr Karen Leslie
> Earth Sciences
> University of Queensland
> St. Lucia, Qld, 4072
> Australia
> E-mail: [log in to unmask]
> www.earth.uq.edu.au
> Tel:    +61 7 336 51132 / 53281
>
>



--
Jason Curtis