Dennis and others,

     For what it's worth, we recently received a EuroVector EA and needed
some CO quickly in order to set it up and test it for oxygen pyrolysis.
The only thing we could come up with quickly was a 2.5 purity tank from
Praxair.  To our surprise it had a very low background for water and O2 and
not much of anything else showed up in the background scans.  In addition,
it turned out to have a very workable d18O value of around +17 per mil.
The delta value is just a rough estimate based on the value we get for our
nitrate oxygen standard but it's certainly not off by hundreds of per mil.
I have no idea if lower purity CO normally has such a workable oxygen
composition or we were just lucky.  If it's the rule rather than the
exception, maybe lower purity CO could be scrubbed for contaminants in the
lab.  The Micromass engineer who installed our instrument  thought he
remembered someone else having the same experience.

                                                        Steve

Steven Silva
U.S. Geological Survey
345 Middlefield Rd., Mailstop 434
Menlo Park, CA 94025
ph:  (650) 329-4558
fax: (650) 329-5590
email: [log in to unmask]





                    "Coleman,
                    Dennis D."             To:     [log in to unmask]
                    <coleman@ISOTEC        cc:
                    HLABS.COM>             Subject:     CO reference for TC/EA
                    Sent by: Stable
                    Isotope
                    Geochemistry
                    <ISOGEOCHEM@LIS
                    T.UVM.EDU>


                    10/26/2000
                    11:32 AM
                    Please respond
                    to Stable
                    Isotope
                    Geochemistry





We have just taken delivery on a TC/EA for our Delta Plus XL and have been
confronted with the problem of finding a CO standard with near-natural
18O/16O.  I know there was some discussion about this topic last spring and
I was wondering if anyone has found a suitable US source, or has worked out
a way to get some of the German gas.  Thanks for your help.

Dennis D. Coleman
Isotech Laboratories, Inc.
1308 Parkland Court
Champaign, IL 61821
phone (217) 398-3490
fax (217) 398-3493
web page: www.isotechlabs.com
email: [log in to unmask]