When converting O2 from a gas mixture, such as the O2-N2 mixture in air, the
gas mixture has to be circulated over heated graphite-Pt by using a pump.
This was noted by Kroopnick in his early paper (in Science) on solubility
fractionation associated with oxygen dissolution. In our experiments (some
done by the Coastal Science group in Austin, TX), we found that a
temperature of 700-800 C with a conversion time of about 10 minutes resulted
in conversion efficiencies of >98% (Aggarwal and Dillon, GCA, 1998).
Removing the CO2 immediately or at the end of the process did not make a
Pradeep K. Aggarwal, Ph.D.
Head, Isotope Hydrology Section
International Atomic Energy Agency
P.O. Box 100 (Please use Box 200 for PERSONAL mail)
Wagramer Strasse 5
A 1400, Vienna, Austria
e-mail: [log in to unmask]
> From: Kinga M Revesz, Chemist, Reston, VA (Kinga Revesz)
> Sent: Wednesday, 24 January 2001 15:32
> To: [log in to unmask]
> Subject: Re: how to convert O2 into CO2
> Sergey and others:
> I agree with Hilary. I remember now, that I had to work with very clean
> O2. When I froze the O2 on mole sieve, after GC separation, I had to
> away He (carrier gas) very very well, that meant around 10 minutes pumping
> after the TC gauge showed no gas. Also, I watched the conversion very
> closely. I timed the activation, and I stopped the reaction the moment
> when the TC gauge showed good vacuum. For explanation see Hilary's note.
> The reaction time of course depended on the amount but usually was very
> fast even on that temperature. Pt catalyst is a must. We used Pt shield.
> Some people say that the volume of the converter is critical. Ours was
> big, but gave good numbers even at 1 micromole O2 conversion.
> Kinga Revesz
> Chemist, Stable Isotope Laboratory
> U.S.Geological Survey
> MS 431
> Reston, VA 20192
> FAX: 703-648-5274
> Stuart-Williams To:
> [log in to unmask]
> <h.stuart-williams@ cc:
> UEA.AC.UK> Subject: Re: how to
> convert O2 into CO2
> Sent by: Stable
> <[log in to unmask]
> 01/24/01 03:30 AM
> Please respond to
> Stable Isotope
> With regard to the following :
> I have used old carbon spectrograph rods soaked in platinum chloride for
> the O2 - CO2 conversion on a BrF5 line. I found that even with the
> platinum catalyst that lower temperatures produced a more complete
> conversion. Some workers prefer to time the reaction, supposedly for
> reproducibility, but I found it better to stop as soon as the pressure
> starts to rise again. This is because even tiny amounts of a non-reactive
> gas, such as nitrogen, slow the process enormously. As the impurities are
> variable, the time is variable. On that subject, you must have relatively
> pure O2. Otherwise it appears that the inert gas is swept to the freezing
> surface in the LN2 and largely blocks freezing down of the CO2. This
> ultimately leads to substantial CO production.
> Hliary S_W
> At 12:54 24/01/01 +1300, you wrote:
> >Dear Sergey and Kinga,
> >you could surely use much higher temperature but with a catalyst (Pt
> >solution), gaining much time. See the literature on O-isotopes in
> silicates or
> >anyone who knows that procedure.
> >Peter B.
> >c/ IGNS, Lower Hutt, New Zealand
> Hilary Le Q. Stuart-Williams Ph.D.
> (Climate, behaviour study and ecology using stable isotopes)
> Research Officer - Stable Isotope Laboratory
> School of Environmental Sciences, University of East Anglia
> Norwich NR4 7TJ, England
> Telephone 01603 593837 (Work), 01603 507719 (Fax)
> 01603 503430 (Home)
> More data at : www.uea.ac.uk/~sil/