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Hello Marc,

Don't forget that it is the comparison between sample and reference CO2 that is being measured. 12C16O17O will contribute ~6.5% to the total m/z 45 beam for the reference as well as for the sample. 

The most comprehensive paper available on the subject of the 17O correction to δ13C measurements of CO2 is by Jan Kaiser (Geochimica et Cosmochimica Acta, Vol. 72 (2009), 1312–1334). You'll find all the background details (and reference to earlier work) in there. The latest IUPAC recommendations on this correction have just been published, by Brand et al. (Pure & Applied Chemistry, Vol. 82, 1719–1733).

I hope that this helps.

Regards,
Martin Miller


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Martin F. Miller
British Antarctic Survey,
High Cross, Madingley Road,
Cambridge CB3 0ET
United Kingdom

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Visiting Research Associate,
Planetary and Space Sciences Research Institute,
The Open University,
Walton Hall,
Milton Keynes MK7 6AA

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-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Ruppenthal, Marc
Sent: 30 July 2010 12:15
To: [log in to unmask]
Subject: impact of Craigs correction on delta13C values

Hello all,
sorry for this newbie question:
When comparing delta13C results calculated with Craig´s correction for 12C16O17O in CO2 (interfering with 13C16O16O on mass 45) with delta13C values of the same run but recalculated without Craig´s correction, I do find deviations in the delta13C values between -0.1 and +0.3‰. Since 12C16O17O is said to contribute 6.5% to the total mass 45 beam, I was wondering why the deviations in my delta13C values are comparably small. Of course, this might be coincidence, but I would be interested to know how large the deviation between corrected and uncorrected values can get. Is part of the deviation cancelled out due to the normalization? Is everybody measuring with Craig´s correction (or related, more recent correction algorithms) or are there also people who do not use it due to whatever reason? I do not know where I could look to find it out; therefore I am asking the great isogeochem list... :-)
Many thanks in advance!
Sincerely,
Marc Ruppenthal


___________________________________

Dipl.-Geograph Marc Ruppenthal

AG Jun.-Prof. Dr. Y. Oelmann
Institut für Integrierte Naturwissenschaften
Abteilung Geographie
Universitätsstraße 1
56070 Koblenz
Germany

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