I would just like to describe my experience measuring 18O in tree ring
cellulose and state my complete agreement with Pier's comments below and
Willi Brand's reply also posted to ISOGEOCHEM.
We keep all cellulose samples dry in desiccators for a least several
weeks before analysis to dry them out. Them we do the analysis
using a sealed sampler in Helium to keep the samples dry during analysis,
and delay analysis for three hours after transferring the samples and
standards from the desiccator to the sampler. So I regard all
comments on the problems of water build up in the cellulose as being
In addition there are numerous other problems:
We use a low temperature furnace (1130 degree C) with a nickel carbon
catalyst as used for %O analysis for organic compounds, and have had to
add a) doping of helium carrier gas with chloropentante to improve
results and reduce memory effects, b) use tin capsules to avoid problems
of shiver build up, c) use of a Porapak QS column before a molecular
sieve column to separate organic contaminants from the CO, and then d)
back flushing of these columns to get rid of the contaminants, e)
different sized standards to correct for the non-linearity of CO in the
source of the mass spectrometer, and f) a very complex post analysis
spreadsheet that corrects for non-linearity and drift of the high and low
calibration standards drifting at different rates. An example of
this spreadsheet "Generic Template Berkeley 1.00" can be
We have had poor results trying to use standards other than cellulose and
now use three standards:
high standard) IAEA C3 which we assign a value the 32.2
VSMOW to, based on the average value in the literature, we have not yet
calibrated successfully with IAEA 601 and 602, (see problem described
low standard) A commercially bought Sigma cellulose that we
analyzed against IAEA C3 intensively and have assigned a value of 26.4
delta 18O VSMOW. We have not yet calibrated successfully with IAEA
601 and 602.
quality control) IAEA V9 our quality control standard which
has an average value of 28.57 VSMOW plus or minus 0.21 for all of these
run in the last two years (long term external quality control).
We are confident that these standards are internally reproducible, but
because of the problems that Pier and Willi describe are not quite sure
of an exact number on the VSMOW scale. This is certainly a problem and I
completely agree with Pier that a certified standard, preferably two,
would be desirable. However, Willi's comment that this is difficult
for the international standard is certainly true. However, if we
are trying to analyze cellulose or other organic matter, it would appear
that we have to work out reproducible methods that will remove the effect
of water contamination from organic samples, otherwise the analysis
results may not be useful.
Our standards only cover a small range but 90% of our tree ring standards
fall in this range.
We have found that the benzoic acid seems to analyze differently from
cellulose in our system. For example, the IAEA benzoic acid seem to
have a memory effect we do not see in cellulose. In order to get a
stable number from benzoic acid, it appears we have to analyze at least 3
and preferably 4 standards in a row. Strangely, there even
seem to be a memory effect from the benzoic acid into the cellulose V9
quality control. It appears the analyses including benzoic acid do
not run well and we have been forced to analyze just with the cellulose
standards as I described. Since the structure of benzoic acid is
quite different, we have speculated that it decomposes quite differently
to form CO compared with cellulose.
Do any other labs have 18O numbers for IAEA C3 and IAEA V9?
I would have to say that this analysis is not for the faint of
heart! However, good for those who enjoy a challenge.
I can send you a power point describing our method off list if you
Hope this helps,
At 01:18 PM 3/24/2008, you wrote:
Center for Stable Isotope Biogeochemistry
The reality is that there is no standard. The only way one can go is
'calibrate' a 'local working standard (cellulose)' against the
scale. The problem is here the comparison of two different materials
different matrices, or in other words comparing apples with
There clearly is a need for certified reference material for d18O in
cellulose. Storing cellulose is not straightforward, since it is
hygroscopic (which basically does not effect the d13C, but does the
one of the reasons we have no cellulose standard available for
What people do is comparing with each other (e.g. Robin-round), but that
no calibration. It creates a 'sub-scale' and the data obtained that way
fact cannot be used for comparison with anybody not included in the
robin-round. Also, it introdices more uncertainty in measurements if
'local-scale' is calibrated against the international scale (more steps
traceability chain increase the combined uncertainty of a measurement).
applying thermometry with such data, the result is very uncertain
useless, because all thermometers are calibrated to the international
and not to a local scale), and no small temperature differences can
determined in any way.
Of course, if only used for comparison of measurements made by the
method in the same laboratory, only repeatability is sufficient. But
temperature determination can be done than, only relative difference can
determined on the 'local' measurements.
I will explain matters like this in the short course that will be
by Bob Vocke and myself at the EGU2008 (13-18 April, in Vienna).
We really need a better situation here....
Delta Isotopes Consultancy
Dr. Pier A. de Groot
Pastoor Moorkensstraat 16
2400 Mol - Achterbos
Tel. +32 (0)14 326 205
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Associate editor for stable isotopes of eEarth on-line magazine
Head of Isotopes in Geosciences of the European Geoscience Union
EGU Home web-site:
Isotope program for the EGU2008 General Assemblee can be found at:
Organization Committee member of BASIS (Benelux Association of
Visit my WEB-site about my ³Handbook of Stable Isotope Analytical
Techniques², with a link to the Elsevier web site on the handbook
last update: August 15, 2005
Volume I is available. Volume II is in press and will be available
half of 2008.
> From: Simon Poulson <[log in to unmask]>
> Reply-To: Stable Isotope Geochemistry
<[log in to unmask]>
> Date: Mon, 24 Mar 2008 11:56:57 -0700
> To: <[log in to unmask]>
> Subject: [ISOGEOCHEM] cellulose-d18O standards
> Dear All,
> We were planning to run some cellulose-d18O analyses in our lab,
> I had a question about d18O standards. A number of papers that
> run similar analyses state that they calibrate a working
> standard (e.g. from Aldrich or Sigma) for d18O and use this
> running samples, but the papers don't say what standard they use
> calibrate this working standard.
> Cellulose standard IAEA-CH-3 is available from IAEA, but is
> for d13C only, not d18O. Is there a consensus d18O value that
> use for this standard? Or do people use other certified
> such as benzoic acid IAEA-601 (+23.3 per mil), or barium
> NBS-127? (+9.3 per mil)
> Thanks in advance for any comments and suggestions.
> Simon Poulson
> Simon Poulson
> Research Associate Professor
> Dept. of Geological Sciences & Engineering MS-172
> University of Nevada - Reno
> 1664 N. Virginia St.
> Reno, NV 89557-0138. USA
> (775) 784-1104
> Fax: (775) 784-1833
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