As far as I'm aware the IAEA C3 standard is holocellulose rather
than alpha-cellulose. Therefore there will be some hemicelluloses present
and it will not be truly homogeneous. However, these differences in
structure may not be significant. We measured the 13C/12C values from a
nitrated sample of it: 

Mean       -24.78
n          14
s.d.(n-1)  0.11

However, 13C/12C values from nitrated samples would appear to be depleted
by 0.30 per mille (Palaoklimaforschung 15, 141-155). 
	We decided to use a commercial alpha-cellulose as a standard
(Sigma Cellulose ref 92F 0243) and typically have a precision of 0.05 per
mille on 13C/12C measurements... Let me know if you want some. Best


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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