I'm preparing to make 18O/16O measurements of cellulose and bulk organic
matter (leaves and wood). I've searched the isogeochem archives and I
have a few questions for experienced members of the group.
1) Which reference materials? From what I understand, it's hard to keep
cellulose dry and any water that it absorbs will change the 18O value.
That's why the IAEA doesn't assign values for their cellulose reference
material (only 13C values). For that reason, many use benzoic acid or
water in silver tubes. But neither of those materials are at all close
to behaving like cellulose in the combustion process. So, seems like
there is no perfect answer here. I'm leaning toward VSMOW and VSLAP in
silver tubes from USGS. If so, what size (0.15 uL or 0.25 uL)?
2) Working standards? I have some cellulose from Sigma. I assume this
needs to be dried in a desiccator for a few days. I also read that
granulated sugar from the grocery store could work. Does this need to
be ground finely?
3) Sample + reference storage? Is a desiccator OK? Which kind? Glass
with phosphorous pentoxide or something less hazardous? Or one of the
newer plastic vacuum kind?
4) CO working tank purifying scrubs? Something to remove trace water
and organics, but I can't find this thread for details right now.
5) CO working tank isotopic composition? How important is this? And how
do you predict what the approximate value will be when ordering?
6) Autosampler environmental control? I suppose we could purge with He,
or heat and evacuate the carousel. Pros/cons?
Thanks in advance.
Dr. Lisa Welp, Assistant Professor
Earth, Atmospheric, and Planetary Sciences
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