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,
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
E-mail: [log in to unmask]
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
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?
Roy Faiman, Ph.D
Laboratory of Malaria and Vector Research
NIAID, National Institutes of Health
12735 Twinbrook Parkway, 2W-09C
Rockville, MD 20852 USA
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