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!
Andrew