Roland and Willi,

We have gone through about 6 tanks of CO here at NCSU in an effort to find
an appropriate IRMS instrument standard gas, all appear to have an isotopic
composition of ~ -500 per mil O-18 SMOW or less.  These tanks did not give
good reproducibility with solid or liquid O-18 stds in the TC-EA.  These
tanks also appear to have ~ 10 ppm or greater N2 contamination.

We finally found a supplier that could certify < 5 ppm N2 for a CO tank.
This tank runs well and has an apparent isotopic composition of ~ -230 per
mil.  Do you know what the N2 conc in your CO tank is?  It appears that
small amounts of N2 can cause large apparent O-18 isotopic shifts.  It also
appears that in the US there is trouble with varying amounts of N2
contamination in our CO.  Douthitt was looking into importing CO from a
German supplier, what has happened with that?  We would buy a tank.

Bill Showers

At 03:03 PM 03/15/2000 +0100, you wrote:
>Dear Robert and other friends from Moscow / Idaho,
>
>European CO has a very natural 18O signature. We for instance have a gas
>here from Messer, Germany, at +7.5 per mill vs VSMOW. We can easily
>think of other values produced from natural material such as +40 (from
>CO2 in air), +23 (from O2) or around 0 per mill when formed from water.
>But how on earth can a 18O value of -500 per mill for CO from natural
>sources be understood when assuming no N2 contribution? Who can comment
>on this?
>
>Roland and Willi
>
>--
>‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰
>Roland A. Werner ([log in to unmask]) and
>Willi A. Brand, Stable Isotope Laboratory       [log in to unmask]
>Max-Planck-Institute for Biogeochemistry
>Carl-Zeiss-Promenade 10, 07745 Jena, Germany    Tel   +49-3641-643718
>P.O.Box 100164, 07701 Jena, Germany             Fax:  +49-3641-643710
>‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰
>
----------------------------------------------------------
William J. Showers
Dept. of Marine, Earth, & Atm Sciences
North Carolina State University

(919) 515-7143 - voice
(919) 515-7802 - fax
[log in to unmask] - email