Thank you all for the very helpful and generous replies!  This 
discussion is turning to a very informative thread.

To recap, it sounds like I am right in thinking that it is nearly 
impossible to shift the sample that much, especially when the bulk and 
exchange experiments were run at the same time.  So one explanation is 
that the the original exchangeable fraction was underestimated, even 
though there was a 4-day equilibration with the waters.  An alternative 
explanation might be that one of the runs wasn't fully dry...  It sounds 
like this is more likely on the exchange experiment?  I'm less inclined 
to lay the blame at microbes because I can't imagine the material being 
at all labile.

I should also point out that this was not the only sample that left me 
puzzled.  For example, I also had some dried algae - again this should 
have been crisped up well based on several days of drying oven treatment 
- and it too came back with a low exchangeable fraction 0.02 with a 
2H_true of -191.05, yet a value of -212.63 when re-run in bulk.

In total, for 11 of 12 samples run in my exchange experiment, there was 
a strong shift to more negative values of H_total as compared with 
H_true from the exchange experiment.  Nonetheless, the two sets of 
values were highly correlated (R2 = 0.92), leading me to believe them.  
But I'm not sure where that leaves me...

Best wishes
Andrew



On 2018-12-20 10:25, Wolfram Meier-Augenstein (pals) wrote:
> Given the prior exchanges on this subject, I think it is fair to say
> it is not feasible for an organic sample to experience a shift in
> d2H(total) from -177.8 to -190 merely by sitting on a lab bench
> somewhere (unless the lab is located on the Northern edge of Greenland
> or in Antarctica, the exchange rate at ambient temperature is 0.24 and
> ambient humidity has a d2H value of -230).
> 
> Based on the difference between -177.8 and -190, a potential
> explanation could be linked to scale calibration of lack of.  Assuming
> measured d2H values of the rerun had not been scale calibrated to
> VSMOW/SLAP but the original analyses had been, it wouldn't take much
> (d2Hvsmow = 1.0705 × d2Hmeasured +0.3854) for a scale-normalized d2H
> of -177.8 to correspond to a measured d2H of -190.
> 
> My SWAG would be (based on the assumption the original work did not
> suffer from any artefacts and all measured d2H were properly scale
> normalized) the re-run d2H value of -190 may be the result of microbes
> having munched away at the leaf litter (having survived the process
> associated with equilibration). The operative words here are "SWAG"
> and "may be". ;-)
> 
> 
> 
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
> Behalf Of Wolfram Meier-Augenstein (pals)
> Sent: 19 December 2018 20:47
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] help interpreting 2H exchange exp't
> 
> Dear Andrew,
> 
> 
> I have a swag (scientific wild ass guess) but would need to ask even
> more questions.  Rather than boring the list stiff I will send you an
> e-mail off-list.  You can always share the outcome once we figured out
> what the story is.
> 
> 
> Best,
> 
> Wolfram
> 
> 
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
> Behalf Of A.J. Tanentzap
> Sent: 19 December 2018 20:11
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] help interpreting 2H exchange exp't
> 
> Dear Wolfram
> 
> Thanks so much for the quick reply.  Happy to share in case someone
> else has this question in the future.
> 
> The sample was leaf litter - sorry didn't want to bog down in 
> specifics.
> 
> The d2H values of the 2 waters were -196.1 and 14.5.  And the total 2H
> values were -177.87 and -177.77, respectively.
> 
> Best wishes
> Andrew
> 
> 
> 
> On 2018-12-19 19:55, Wolfram Meier-Augenstein (pals) wrote:
>> Dear Andrew,
>> 
>> 
>> To help you with your question one would need to know a few more
>> specifics such as chemical nature of the organic solid and d2H values
>> of the 2 waters A and B used for the exchange experiment for starters.
>> 
>> You are welcome to contact me off-line if you feel you cannot share
>> the specifics of your experiment with the list.
>> 
>> 
>> Best,
>> 
>> Wolfram
>> 
>> 
>> 
>> ******************************************************
>> Prof. Dr W Meier-Augenstein, CChem, FRSC Stable Isotope Forensics &
>> Analytical Sciences
>> 
>> Robert Gordon University
>> School of Pharmacy and Life Sciences
>> The Ian Wood Building
>> Garthdee Road
>> Aberdeen
>> AB10 7GJ
>> 
>> E-mail:   [log in to unmask]
>> 
>> 
>> 
>> ________________________________________
>> From: Stable Isotope Geochemistry <[log in to unmask]> on behalf
>> of A.J. Tanentzap <[log in to unmask]>
>> Sent: 19 December 2018 19:35:02
>> 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!
>> Andrew
>> 
>> ----------
>> 
>> This email has been scanned for spam and viruses by Proofpoint
>> Essentials. Visit the following link to report this email as spam:
>> https://eu1.proofpointessentials.com/index01.php?mod_id=11&mod_option=
>> logitem&mail_id=1545248132-5yKLNHey8OjX&r_address=w.meier-augenstein%4
>> 0rgu.ac.uk&report=1
>> 
>> ________________________________
>> 
>> Robert Gordon University has been awarded a TEF Gold award for the
>> quality of its undergraduate teaching and learning, placing it in the
>> top 20% of Universities in the UK
>> 
>> 
>> Robert Gordon University, a Scottish charity registered under charity
>> number SC 013781.
>> 
>> This e-mail and any attachment is for authorised use by the intended
>> recipient(s) only. It may contain proprietary material, confidential
>> information and/or be subject to legal privilege. It should not be
>> copied, disclosed to, retained or used by, any other party. If you are
>> not an intended recipient then please promptly delete this e-mail and
>> any attachment and all copies and inform the sender. Please note that
>> any views or opinions presented in this email are solely those of the
>> author and do not necessarily represent those of Robert Gordon
>> University. Thank you.
> 
> ----------
> 
> This email has been scanned for spam and viruses by Proofpoint
> Essentials. Visit the following link to report this email as spam:
> https://eu1.proofpointessentials.com/index01.php?mod_id=11&mod_option=logitem&mail_id=1545250313-RNY-yL0a20yq&r_address=w.meier-augenstein%40rgu.ac.uk&report=1
> 
> ________________________________
> 
> Robert Gordon University has been awarded a TEF Gold award for the
> quality of its undergraduate teaching and learning, placing it in the
> top 20% of Universities in the UK
> 
> 
> Robert Gordon University, a Scottish charity registered under charity
> number SC 013781.
> 
> This e-mail and any attachment is for authorised use by the intended
> recipient(s) only. It may contain proprietary material, confidential
> information and/or be subject to legal privilege. It should not be
> copied, disclosed to, retained or used by, any other party. If you are
> not an intended recipient then please promptly delete this e-mail and
> any attachment and all copies and inform the sender. Please note that
> any views or opinions presented in this email are solely those of the
> author and do not necessarily represent those of Robert Gordon
> University. Thank you.