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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
>
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