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Thu, 15 Jan 1998 14:53:23 +0100 |
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Dear all,
The growing use of continuous flow EA-IRMS to measure oxygen isotope
ratios of cellulose and other organic materials (there are 3 labs set up to
do this here in central Switzerland alone) points out the need for a set of
standard materials we can all use for interlaboratory calibration. We
would like to start a discussion of how best to do this, and also hopefully
spur some genuine action.
Our own experience suggests that a minimum of two well-characterized
standards, the isotopic values of which lie at opposite extremes of the
range of natural variation, are required. We have found that while the
absolute isotopic values of cellulose standards relative to our standard
gas may vary, the absolute difference between two standards remains quite
constant. Furthermore, when the measured values are plotted against the
true isotopic values, the slope of the resultant line is very close to one
( 0.96 or better). Thus, measuring two fairly distant standards during
routine analyses should be sufficient to calibrate measured back to VSMOW
or PDB. Including a third standard would be even better.
So, what do we need?
1) We need fairly large quantities of (at least) two potential sample
materials. Whether it is best that they be natural (tree cellulose from a
high latitude site and from an equatorial site?) or synthetic, I am not sure.
2) The materials would need to be analyzed by traditional
techniques by a
number of laboratories to establish the true 18O/16O ratios (volunteers?).
3) Some central repository is required for storage and distribution
(IAEA?).
4) ????
Obviously, small aliquots of the standards could then be distributed to
labs for calibration of larger quantities of in-house standards for routine
analyses.
We are certain that we are not the only labs facing standardization
problems, and hope that we can collectively come up with some solutions.
Stephen Burns and William Anderson
Geologisches Insitut Geologisches Institut
Universitat Bern ETH-Zentrum
CH-3012 Bern CH-8092 Zuerich
Switzerland Switzerland
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Dr. Stephen J. Burns
Stable Isotope Laboratory
Geological Institute
University of Berne
Baltzerstrasse 1
CH-3012 Berne, Switzerland
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