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Stable Isotope Geochemistry

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On Thu, 9 May 1996, Tom Edwards wrote:

 > 1.  First, a caution:  Carbon-isotope homogeneity in a natural cellulose 
> may not be a good indication of oxygen- or hydrogen-isotope 
> homogeneity (which seemed to be implied by one recent comment).  

.... also found for oxygen isotopes (approx 0.2 per mille). Hydrogen has
not yet been determined. However, it should be noted that this was for
alpha-cellulose extracted from the annual latewood samples of oak. High
resolution oak intra-ring carbon isotope variability has been investigated
(Ogle 1994, Loader 1995...) but for annual climatic reconstruction it is
impractical to use smaller samples. The method of sample preparation
utilising an ultra-sonic bath was to illustrate that there are possible
alternatives to grinding small samples (around 50 mg). 

	It is unlikely that there will be an international cellulose
nitrate standard due to its unstable nature and decomposition on long-term
storage. Still, that's saved us from a few 1920's movies! The IAEA-C3
holocellulose standard has been used as a standard at several labs,
although clearly not for hydrogen. If there are plans to produce a future
standard could this be done synthetically as recently reported
(International Journal of Biological Macromolecules 1995, 17: 373-379)?
Perhaps a biochemist could come to the rescue? 

Iain

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Iain Robertson                                + 
Godwin Institute for Quaternary Research,     +
University of Cambridge, Free School Lane,    + Tel. ++ 44 (0)1223 334881 
Cambridge, UNITED KINGDOM CB2 3RS             + Fax. ++ 44 (0)1223 334871 
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Godwin Institute homepage              http://www.esc.cam.ac.uk/GIQR.html
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