Dear Oliver,
In fact, this is rather difficult matter. I try to give some answers.
first, there is a very useful web-tool created by Mike Verkouteren,
http://www.cstl.nist.gov/div837/837.01/outputs/standards/algorithm/algorithm.html
see also Verkouteren, R.M., and J.N. Lee, (2001) Web-based interactive
data processing: application to stable isotope metrology, Fresenius J.
Anal. Chem., 370 (7), 803-810.
Here you can make calculations.
second, you can find some information in the review we have published
recently:
Assonov, S.S., and C.A.M. Brenninkmeijer, (2003a) On the 17O correction
for CO2 mass spectrometric isotopic analysis, Rapid Commun. Mass
Spectrom., 17 (10), 1007-1016.
as well as a re-determination of the required value of 17R
Assonov, S.S., and C.A.M. Brenninkmeijer, (2003b) A re-determination of
absolute values for 17RVPDB-CO2 and 17RVSMOW, Rapid Commun. Mass
Spectrom., 17 (10), 1017-1029.
The later article also demonstrates a magnitude of a d13C bias among
different 17O correction algorithms.
I can send you the papers off-list.
Third, please note that the linkage between NBS-19-CO2, working
reference and your sample should be done consistently, namely tracing
raw d45 and d46 values measured on the sample back to the primary
reference, in our case NBS-19-CO2.
Here ISODAT seems provide a bad service - this linking chain appears to
be hidden, and that may cause some errors.
Some ideas why this linkage is of primary importance you can find in
Verkouteren, R.M., and J.N. Lee, (2001) as well as in Assonov, S.S., and
C.A.M. Brenninkmeijer, (2003a).
See also Allison, C.E., R.J. Francey, and H.A.J. Meijer, (1995)
Recommendation for the reporting of stable isotope measurements of
carbon and oxygen in CO2 gas., pp. 155-162, IAEA-TECDOC-825, Vienna.
Best regards,
Sergey Assonov
PS: in order to ask files, you can contact me of-list.
Oliver Brendel wrote:
>Dear isogeochem subscribers,
>
>does anybody know how the ISODAT software calculates the 17O
>correction for d13C values ?
>We have tried to calculate this correction following the indications given
>in the manual, but we don't get the same values.
>So, does anybody have the exact equations ( or EXCEL spread
>sheet)?
>
>And is anybody using other values for a and K than 0.516 and
>0.0099235 and if yes, why ?
>
>Thanks for any help
>
>Oliver Brendel
>
>________________________________________________________
>_
>Oliver Brendel UMR Ecologie et Ecophysiologie Forestiere
>INRA - Centre de Nancy 54280 Champenoux France
>[log in to unmask] TEL 0033/383/394041-4201 FAX /394069
>
>
>
>
--
----------------------------------------
Dr. S. S. Assonov,
Abteilung fuer Luftchemie,
Max-Planck-Intitut fuer Chemie,
J.J.Becher Weg 27,
55128 Mainz, Germany
Phone: +49-6131-305-495 (office)
+49-6131-305-472 (lab)
Fax: +49-6131-305-436
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