Tim Heaton wrote:

> Paul
>
> I see that Willi Brand has responded to your query with news that
> Linde supply H2 with a dD value of -220 per mil.
>
> A few years ago Willi organised a 'ring test' (via Isogeochem) of
> hydrogen gas samples supplied by Messer Griesheim. One of these
> (ISO-TOP Ring-test Gas-A) has a dD value very close to SMOW, and we
> have been using this (the cylinder contains about 1 litre at 12 bars)
> ever since as our reference.
>
> Willi - is this gas still available?
>
> Tim Heaton
>
> NERC Isotope Geosciences Laboratory
> British Geological Survey
> Keyworth, Nottingham NG12 5GG, England
>
> Tel. +44(0)115 936 3401
> Fax +44(0)115 936 3302
> E-mail: [log in to unmask]

Dear Tim et al,
The gases for the ring test were a one time manufacture at Messer
Griesheim. Although they still might have some of the flasks left from
that filling procedure, I would not trust the numbers any more. (It is
not wise anyway to rely on the isotope ratio value of a gas over years,
in particular not  for hydrogen). Under the brand name 'ISO-TOP' Messer
Griesheim manufactures gases with an isotopic composition at or at least
close to the desired delta value.
Regards    Willi

P.S. Together with Ty Coplen I have summarized the results of the ring
test for an IAEA Tec Doc report some time ago. I hope it will become
available this year. WB

--
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Willi A. Brand, Stable Isotope Laboratory       [log in to unmask]
Max-Planck-Institute for Biogeochemistry
Tatzendpromenade 1a, 07745 Jena, Germany        Tel   +49-3641-643718
P.O.Box 100164, 07701 Jena, Germany             Fax:  +49-3641-643710
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