Dear Russel
We have begun working with biological materials comming from growth chambers.  Because we were new at this it was difficult to assess the end product.  Since we were only looking at about 4 samples to start off with.  This was for 15N.  The samples proved to be WAY WAY too enriched and we wound up scrapping the combustion column in the EA for natural abundance.  The residuals were causing up to 50 permil increases in the following samples.  The problem is not in the experiment as much as in changing doses and habits of biological researchers regarding the sensitivity of natural abundance IRMS as opposed to  what they are used to with other instruments.  We also did a D/H in urine experiment for Human Kinetics, where the experimenter followed my suggestions and it worked well.  Because the experiment is a tracer-tracee type of test, it turns out that the same results are accomplished using % OR delta permil in their calculations since in some cases the units cancel and give identical factors at the end.

In other words, they need to adapt to the high precision of natural abundance instruments, not the other way around.  I'm giving a course next week touching on this and other aspects for biological users at our Faculty.  I hope to present some form of comparison table(s) in Excel similar to the one compiled by Richard Reesman of Geochron Labs in the 80s for the 5th CF Workshop.  Something everyone can use, I hope....

Good luck
Gilles
-----Message d'origine-----
De:     Russell Frew [SMTP:[log in to unmask]]
Date:   22 avr. 1998 16:24
À:    [log in to unmask]
Objet:  isotopically enriched samples

Dear All

I am setting up a lab with a single irms equipped for dual inlet and
continuous flow work via an elemental analyser (Carlo Erba). My
interests are environmental samples at natural abundances.
I have been approached by a physical education student wanting to do
a metabolism study using artificially enrich sucrose (around 1% 13C).
The analyses would be of blood  glucose and breath samples.

My question is, is this type of work compatible with natural
abundance work? My training in trace analysis of metals in seawater
has made me paranoid about contamination. Is there a concern here?

I would greatly appreciate hearing your thoughts/experiences.

regards

Russell Frew
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Dr Russell Frew                   [log in to unmask]
Department of Chemistry
University of Otago                      ph  64-3-479-7913
P.O. Box 56                             fax  64-3-479-7906
Dunedin, New Zealand
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