I appreciate all of the responses to my email asking if anyone had measured
cotton cellulose (IAEA-V-9) for delta 13C.  It sounds like no one has used
this as a stable carbon isotope standard as yet.  As someone pointed out
there is an IAEA-C3 cellulose standard with a reported (in the IAEA AQCS
catalog) delta 13C value of -24.91 with standard deviation of 0.49 per mil.
I presume that this variation results from isotopic inhomogeneities in the
cellulose.  Do others who use this standard see that much variability?

In terms of the cotton cellulose standard, it may be worth sending it
around to be measured.  It comes very finely ground, and thus potentially
somewhat more homogenized.  I don't know much about how these standards are
made, however.  If the standard is made for trace elements, I presume that
is what is controlled for, not isotopic ratios.  My bottle may be one
value, but another bottle may be slightly different, unless there is only
one master batch that is mixed up and is then divided.

What do people think about the utility of another C3 cellulose standard
(besides the existing IAEA-C3 standard (among others)?) The cotton
cellulose could be less variable.  It may be more useful, however, to look
for a good C4 standard that we could send around instead.

Francesca



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Francesca Smith

Current address:                Department affiliation:

INSTAAR                         Department of Geophysical Sciences
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