Hi

I agree with most comments so far but would add that we typically use 
sucrose as our oxygen isotope standards in most runs of organic 
material.  This seems to have a reasonable accuracy and precision if 
well cared for, and is appears to be less hygroscopic than cellulose.  
This probably results from having a much lower surface area as it is 
crystalline and not based on micro-fibres.  As cellulose is a glucose 
polymer, I think it reasonable to assume that decomposition of sucrose 
(fructose/glucose dimer) and cellulose is reasonably similar under 
pyrolysis.

It is pretty clear that you cannot produce, much less store, a 
water-free cellulose.  The relationship between water and the cellulose 
structure is much too intimate.

Please feel free to disagree: Willi, Tyler and I have discussed the use 
of sucrose as an 18O standard at some length and it was NOT included in 
the IUPAC study that Willi mentioned because of its limitations.

Like Paul, we try to keep our standard dry and emphasise repeatability 
of handling.

We have a working value of 36.4 permil VSMOW for the ANU Sucrose 
standard, which I believe is similar to IAEA-CH-6?

Hil

-- 
Hilary Stuart-Williams PhD
Research Officer - Stable Isotopes
Environmental Biology Group
Research School of Biological Sciences
The Australian National University
Acton, Canberra
Australia ACT 2601
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