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?