Hi Andrew - the devil is always in the prep and analysis details.  Something seems wrong to me with such a low exch-H fraction.  What is the residual moisture content (gravimetrically)?  How did you treat / dry the sample, etc. It's also possible - by a fluke  - that the H isotope fractionations of the 2 waters you used landed you right on the identical value of the non-exch H. I would go far outside the natural range - i.e. very positive on one of the waters (like +500). Len

-----Original Message-----
From: Stable Isotope Geochemistry <[log in to unmask]> On Behalf Of A.J. Tanentzap
Sent: Wednesday, 19 December 2018 20:35
To: [log in to unmask]
Subject: [ISOGEOCHEM] help interpreting 2H exchange exp't

Dear all

I've run an exchange experiment on a solid organic as described in Meier-Augenstein et al. 2011. Rapid Commun Mass Spectrom.

I estimated the non-exchangeable 2H ratio to be -178.  The estimated fraction of exchangeable H in the sample was 0.0005.

When I re-run the sample in a bulk analysis, the total (i.e.
exchangeable + non-exchangeable) ratio was -190.

Would someone be so kind as to explain how this is possible with a near-zero fraction of exchangeable H?

Many thanks!
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