Dear Alex,
 
 
I see what you mean. Put like that you are right. A measurement of an aliquot (150 - 180 nL) by reduction-IRMS does not necessarily proof exchange, only good and efficient mixing.
 
OK, rephrase my previous post and replace "exchanged" with "mixed" (well and fast).
 
 
Best,
 
Wolfram

________________________________

From: Stable Isotope Geochemistry on behalf of [log in to unmask]
Sent: Thu 22/10/2009 16:57
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Exchange D2O-HDO



Dear Wolfram

Thanks for the info, but please let me be devils advocat, since it
illustrates my question:

If I understood you right and if you measured with a mass spec either
after reduction or after catalyst equilibration with H2, this finding is
no proof that the exchange reaction takes place at all. It simply
demonstrates that D2O and H2O molecuels mix in a fast manner. I am sure
you introduced more than 1e15 water molecules into your system, an there
is no question that this will convert nicely to well mixed HD even if
only H2O molecules and D2O molecules (and not a single HDO) reaches your
reactor or your catalyst. Because you can crack D2O and H2O into HD and
OH and OD without creating HDO in between.

Does this make the problem clearer?

Axel


'''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Axel Suckow
Isotope Hydrologist, Geochronologist
Isotope Hydrology Laboratory
International Atomic Energy Agency
Wagramer Strasse 5
A-1400 Vienna
Austria
Phone: 0043 1 2600 21759 (desk) or 26762 (mass spec)
email: [log in to unmask]
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''


> -----Original Message-----
> From: Stable Isotope Geochemistry
> [mailto:[log in to unmask]] On Behalf Of Wolfram Meier-Augenstein
> Sent: Thursday, 22 October 2009 16:33
> To: [log in to unmask]
> Subject: Re: Exchange D2O-HDO
>
> 
> Dear Alex,
> 
> 
> We haven't measured the kinetics of this reaction but I can
> tell you from our observations with preparing spiked water
> for physiological/metabolic studies that full exchange or
> equilibration should happen within a matter of hours if not minutes.
> 
> We prepare spiked water aiming for a d2H-value of approx. 300
> o/oo so as to stay close to natural conditions as possible
> (since it is anybody's guess how pools and fluxes might be
> influenced by "unphysiologically" high levels of 2H).
> 
> To this end we mix approx. 1.2 mL of 90 at% D2O with 19.9988
> L of water with a d2H value of -54 o/oo.  Basically we add
> the tracer to 10 L of water and then add the remainder of
> 9.9988 L relying on the resulting turbulences for mixing. The
> theoretical expected d2H value for the mix is +296 o/oo
> (which assumes the 09 at% D2O is indeed 90 at%) and samples
> taken from the bottom outlet of the reservoir within minutes
> of this procedure are usually within +/- 20 o/oo of this value.
> 
> 
> Best,
> 
> Wolfram
> 
> 
> ****************************************
> "Facts do not cease to exist because they are ignored."
>
> Aldous Huxley, "Proper Studies", 1927
> ****************************************
> Dr W Meier-Augenstein, CChem, FRSC
> Principal Scientist - Stable Isotopes
> Stable Isotope Laboratory
> SCRI
> Invergowrie
> Dundee, DD2 5DA
> United Kingdom
> Tel.: +44 (0)1382 560025
> Fax: +44 (0)1382 568544
> Email: [log in to unmask]
> 
> Senior Lecturer (Associate Professor) - Stable Isotope
> Forensics Centre for Anatomy & Human Identification
> University of Dundee http://www.lifesci.dundee.ac.uk/CAHId/
> <http://www.lifesci.dundee.ac.uk/CAHId/>
> 
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>
> From: Stable Isotope Geochemistry on behalf of [log in to unmask]
> Sent: Thu 22/10/2009 14:38
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] Exchange D2O-HDO
>
>
> Dear IsoGeoChemists
> 
> some years ago in Isogeochem I remember a discussion
> concerning the details what happens when we mix isotopically
> spiked water, e.g. D2O, with normal water. There was
> discussion how fast the mixing is, and part of the discussion
> dealt with the question if D2O will be preserved as D2O among
> many "normal" H2O molecules or how fast the D2O will exchange
> one of his D with a normal H2O to form two HDO.
> 
> Here is my question:
> 
> Are you aware of any publications that experimentally
> confirms this exchange to really happen and one which perhaps
> gives hints concerning the speed of this exchange D2O+H2O <-> 2 * HDO?
> 
> I imagine this is not an easy task to be done experimentally,
> at least with a mass spec, because we have to reduce or
> isotopically exchange the water prior to analysis. CRD laser
> spectrometers could do a better job here since they determine
> the isotopes in the water molecule directly...
> 
> Any hints towards citable experiments are very welcome.
> 
> Thanks
> Axel
>
> 
> '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> Axel Suckow
> Isotope Hydrologist, Geochronologist
> Isotope Hydrology Laboratory
> International Atomic Energy Agency
> Wagramer Strasse 5
> A-1400 Vienna
> Austria
> Phone: 0043 1 2600 21759 (desk) or 26762 (mass spec)
> email: [log in to unmask] <mailto:[log in to unmask]>
> '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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