Dear Prof.Anderson and John,

Here more precisions concerning the experiments that I will carry on: I
will inject the spikes(oxygen and deuterium (for D2O, a volume of about
15mL)) in a volume of water of about 1000L(groundwater of the aquifer
stored in a tank): if, I well understand your suggestions: I will have to
mix very well "this whole volume" by using for example in my case,a dye in
order to better constrain "the effectiveness of the mixing". After this
mixing, I will inject the whole volume in the aquifer, I will wait one to
two weeks, and finally I will pump a certain volume of water...to carry
out isotopic analysis.

So, I can suppose that the exchange isotopic reaction will be complete and
sufficient fast to transform all the D20 in HDO.

Thanks

Nelly




> At 06:32 PM 4/7/2005, you wrote:
>>Prof. Anderson,
>>I appreciate the references and agree that the mixing was incomplete, and
>>yet in practice D2O dumped into H2O in a continuously bottom-sparged
>>container is mixed well. Thus if one were to prepare such a mixture, say
>>100 ppm D2O in H2O, and either shake or stir as best you can in practice,
>>how long is it until you can be confident that the D is in HDO (say >95%)
>>and how would you measure the kinetics? For Nelly's question, would the
>>probably *very* incomplete mixing in pore spaces suggest that the D2O be
>>mixed with aquifer water before injection?
>
> John:
> We come at this isotope world from very different view points.  Having
> spent most of my time thinking about NMR experiments, we routinely presume
> that the H-D exchange is so fast that it can be considered
> instantaneous.  Thus in a mixture of ethanol and water, the O-H proton on
> ethanol is time averaged with the HOH protons, because the exchange is
> fast
> on the NMR time scale (in this case ~1000 Hz).  We don't have to worry
> about mixing, because our solutions are well mixed before being introduced
> into the instrument and it is the atomic level process that matters.
>
> You are correct, that there are two very different questions about
> reaching
> complete isotopic equilibrium and the rate constants for proton
> transfer.  The crucial question for Nelly is in fact how well mixed the
> solutions become.  Laboratory mixing is highly variable, but fortunately
> can be fairly easily tested with a dye.  The fastest laboratory mixing of
> aqueous solutions is performed at high pressure in stopped-flow or
> quenched-flow instruments, where the mixer has a dead time of ~ 1
> millisecond.  Bench top mixing by hand of modest volumes, < 5 ml, usually
> has dead times of 1-5 seconds.
> I think your experiment with the electrospray is quite good for studying
> the mixing of isotopic waters.  The other idea would be to monitor the
> near
> IR.  HOD absorbs at 1668 nm where D2O's absorbance is minimal (but there
> is
> a background from H2O. Nonetheless, addition of D2O to H2O will result in
> an increase in absorbance at 1668 nm while HOD is formed. Gordon &
> Yamatera
> Anal. Chem. 36, 1866 (1964)  and Northrop DB Bioorg. Chem. 17, 308 (1989)
>
>
>>
>>FWIW the reason I was doing the sparging was method development for some
>>volatiles in groundwater, trying to evaluate the factors affecting the
>>effective volatile Henry's Law constants in order to optimize ranges.
>>
>>Separately, what physical reason can there be that the isotope effects
>> are
>>different for the H3O+ and OH- proton transfer processes? It seems to me
>>that all the chemical-energy or distance-topology reasons have already
>>been taken care of by the differences between the proton rate constants.
>>For illustration I may take half an hour to limp a mile on the hills near
>>my house, while I may stride off a mile in 20 minutes near my friend's
>>house. If I wear a backpack it may me take 45 minutes near my house and
>>half an hour at my friend's. What am I missing?
>
> The fundamental cause of isotope effects is the RELATIVE change in
> vibrational frequencies between the ground state and the transition state
>
>
>
> Isotope effects depend on both the ground state and the transition state
> for the process.  The ground states for:
> H2OH(+) - - HOH
> and
>
> HOH - - - OH(-)
>
> are quite different.  The transition states have no restoring force for
> the
> transferred proton in both cases
> H2O - - - -H(+) - - - - H2O
> and
> HO(-) - - - - H(+) - - - - OH(-)
>
> The best place to begin to understand isotope effects on proton transfer
> is
> Ronnie Bell's book, "The Proton in Chemistry".
>
>
>>***********************************************************************
>>Vernon Anderson
>>      Professor of Biochemistry and Chemistry - CWRU
>>            Phone: 216 368-2599   E-mail:   [log in to unmask]
>>http://www.cwru.edu/med/biochemistry/faculty/anderson.html
>
> ***********************************************************************
> Vernon Anderson
>       Professor of Biochemistry and Chemistry - CWRU
>             Phone: 216 368-2599   E-mail:   [log in to unmask]
> http://www.cwru.edu/med/biochemistry/faculty/anderson.html
>