Dear Roy,
even if the EtOH (pKa of 15.9) in your 80% alcohol would have no impact on hydrogen exchange, the 20% water (pKa of 14) certainly will.
If your 2H label was truly incorporated in all mosquito tissue, any hydrogen exchange during storage in 80% ethanol should still leave the majority of the label in place. There is only one way to find out. Vacuum dry (freeze dry) a few samples and analyse them for 2H.
While strictly speaking the data might be slightly skewed, you should still be in a position to compare and interpret data on a like-for-like basis. Measured d2H values should still be scale normalized to VSMOW/SLAP. The USGS' stable isotope lab in Reston offer reference waters in cold-welded silver tubes that can be run on a TC/EA.
Speaking of which, while convenient to handle silica gel blue is not the best drying agent. While P2O5 (ok, P4O10) is better by a factor of 100t, anhydrous Magnesium Perchlorate is a still better by a factor of 10.
All the 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]
https://www.wiley.com/en-gb/Stable+Isotope+Forensics%3A+Methods+and+Forensic+Applications+of+Stable+Isotope+Analysis%2C+2nd+Edition-p-9781119080206
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From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Faiman, Roy (NIH/NIAID) [F] <[log in to unmask]>
Sent: 13 July 2018 16:47:11
To: [log in to unmask]
Subject: [ISOGEOCHEM] d2H from mosquito samples
Hi,
We are testing 2H enrichment in wild mosquitoes in West Africa as a method to label mosquitoes for life.
So far we have been using desiccated mosquito samples for our analysis, collected alive and kept over silica gel for 2-4 weeks before IRMS (very dry...).
A question arose regarding testing samples that were trapped elsewhere and preserved in 80% EtOH.
Does anyone have an idea if ethanol preservation alters 2H ratios?
Thanks,
Roy
Roy Faiman, Ph.D
Visiting Fellow
Laboratory of Malaria and Vector Research
NIAID, National Institutes of Health
12735 Twinbrook Parkway, 2W-09C
Rockville, MD 20852 USA
+1-240-747-7879
+1-607-793-5252
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