Dear Nori,

with reference to your question concerning the use of Mg-Pt instead of Zn as
a reducing agent for water.


>I have another question regarding H2 isotope analysis. I found a paper
>on new agent for water reduction by Prof. S. Halas in IAEA report
>(IAEA-TECDOC-825),entitled," Reference and intercomparison materials
>for stable isotopes of light elements". In his article, he recommend
>to use Mg-Pt instead of Zn and the agent gives us extraordianry
>precision of hydrogen isotope analysis, let's say, better than +/- 0.2
>permil. Is somebody tried his method and get similar results?  Are
>there any new water reduction technique instead of them?  Thank you
>all in advance for your gread advice.
>
There is a statement in the Halas and Jasinska paper that says:

 "The best accuracy and reproducibility of the new method is somewhat above
the recent precision of the mass spectrometer (1 sigma = 0.2 per mille) at
mass of the reagent of 120 to 140mg." 

However, looking at the results in Table 1 and Figure 1 this cannot be
correct. These data show a marked dependency of the isotope ratio on the
mass of Mg-Pt right up to the upper limit of the study at 200mg.

At the IAEA consultants group meeting in Vienna just before Christmas the
problem of high precision D/H measurements was discussed. All of the direct
reduction methods, using reagents such as Zn, Mn, Cr, perhaps Mg-Pt etc.
seem only capable of producing routine precisions on the order of 1per mille
at best. Results obtained using U furnaces seem consistently to produce much
higher precisions and I have seen data at +/- 0.2 per mille produced by
several labs using this technique.

One method that does seem to offer great promise, with the benefit of ready
automation, is the H2-H2O equilibration technique using a Pt on alumina
catalyst. It also has the benefit that it can be applied directly to brines etc.

Paul Dennis
Stable Isotope Laboratory
Environmental Sciences
University of East Anglia
NORWICH NR4 7TJ