Dear Herb,

Certainly there are a couple of other techniques for hydrogen isotope
analysis. The aim of my question about Cr metal reduction was to see
if there were any developments in that direction; to know about
specifications of the material and its performance in analysis.

This mostly is concentrating on water analysis, although from pers com
(Rob Kreulen) I heard methane can be analysed very well with the Cr
reduction method. Other organic matters I am not certain about - if
possible to vaporize and not containing too much of other components
eventually polluting the Cr or producing unwanted other gas products
with the H2 - it may work well.

A large pile of publications handles the combustion and also pyrolysis
techniques for organic materials. These systems are either on-line
procedures or in separate tubes. And of course elemental analyser type
of procedures, coupled to (GC)-CF-IRMS, have improved the technique
tremendously - special the amount of samples analysed increased with
several orders.

Pyrolysis indeed has the advantage not to bother about reagent. There
are other methods, like the Ni-tube pyrolysis, where H2 diffusing
through the Ni walls can be collected by a glass tube covering the
Ni-tube, and is furhter collected in a vacuum system in the usual way
(e.g. toepler pump, C-grains). And this method can be used both for O
and H isotope analysis.

refs:
Edwards, T.W.D., Buhay, W.M., Elgood, R.J., Jiang, H.B. (1994). An
improved nickel-tube pyrolysis method for oxygen isotope analysis of
organic matter and water. Chem. Geol. (Isot. Geosci. Sect.), 114:
179-183.

Motz, J.E., Edwards, T.W.D. and Buhay, W.M. (1997). Use of nickel-tube
pyrolysis for hydrogen-isootpe analysis of water and other compounds.
Chem. Geol., 140: 145-149.

and references therein.

Of course we also have the H2 - water exchange method, which has the
disadvantage of the need of a relatively large volume of water and a
precise control on temperature during the equilibration.

And for those who have lots of money and can afford the mass specs,
direct injection of water vapor in a MS or even simultaneous O and H
isotope analysis of water in a dual MS set-up can be done, eventually
the water vapor is reduced by a uranium wire fitted in front of the
inlet of the MS to reduce water into H2 - just to name some of the
methods.... of course a nice bunch of problems must be solved in these
methods - but they are tested and used to some extent.

To name some refs for the last technique:
Nief, G. , Botter, R. (1959). Mass spectrometric analysis of simple
hydrogen compounds. Adv. Mass Spectrom., 1: 515-525.

Thurston, W.M. (1970). Automatic mass spectrometric analysis of the
deuterium to hydrogen ratio in natural water. Rev. Sci. Instrum., 41:
963-966.

Hartley, P.E. (1980). Mass spectrometric determination of deuterium in
water at natural levels. Anal. Chem., 52: 2232-2234.

Wong, W.W., Cabrera, M.P., Klein, P.D. (1984). Evaluation of a dual
mass spectrometer system for rapid simultaneous determination of
hydrogen-2/hydrogen-1 and oxygen-18/oxygen-16 ratios in aqueous
samples.

Further there are site specific methods on organic matters by NMR
analysis, AMS methods in development, specific density related method,
etc. etc.

I just want to make clear, I started a specific item from the large
bunch of methods to have specified info. This was related mostly to
water reduction and of course there are many other ways to get to a
proper isotopic value - therefore I have given a very condensed
'review' of some other methods too, tat least to show that we have a
lot to choose if we want to start analysis of a specific isotope in a
choise of materials, and to avoid a one-sided view.
I hope this opens some views for those who are thinking in the only
way they did their analysis.... At least it is not meant to offend
anybody - in specific you Herb - but I like to give my opinion that we
can highlight a large number of different technologies... and that was
not the discussion. Yes, you are free to bring forward other matters,
so maybe I am wrong with bringing forward this opinion - then my
sincere appologizes to all.

Regards to all,
Pier de Groot.
**************************************************************
Dr. P.A. de Groot
University of the Witwatersrand
Economic Geology Research Unit
Department of Geology
Private Bag 3
2050 Johannesburg
South Africa
Tel.    +27 11 7162564
Fax.    +27 11 3391697
E-mail  <[log in to unmask]>

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