Dear all,
I received questions about the conversion of VSMOW into VPDB (or visa versa)
scale. It was noted that a while ago there was discussion already on this
matter on the list, and Ty Coplen presented a corrected equation (caused by
a better measurement of Œabsolute¹ isotopic rations).
What still surprises me in this matter, where we do our best to get this
conversion as good we can, that all equations are given as absolute
conversions. This, unfortunately, gives the impressiuon that we have two
defined absolute scales for O-isotope ratios a situation that physically
cannot exist. We only can have one defined scale (what to my knowledge is
the VSMOW-SLAP scale), and all others must be related to that one, meaning
introduction of uncertainty if converting to that Œsecondary¹ scale (simple
rule of traceability). Now, in all the equations published up to now this
uncertainty is completely left out. There should be a plus/minus added with
equations.
Even better would be to stop using completely this obsolete VPDB sub-scale
for O-isotopes it is just historical and only is continued out of
sentiments and conservatism, and does not add anything else than confusion.
It only introduces serious mistakes, as clearly shown by the conversion
equations, missing the added uncertainty of this conversion....
Is there any conclusion/decision on this important matter by the IUPAC
commission? They should be aware of this wrong representation!
I really hope to get some reactions on this posting. It is an important
subject that should be solved.
I bring this up again because I think it still is not solved it would be
better if an organisation, like for instance IUPAC, is giving the correct
directions in this matter. If these already would exist, I like to hear
where to find it then I must have overlooked one or two things!.
Best wishes,
Pier.
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The programme can be found at: http://meetings.copernicus.org/egu2007
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Isotopes in Geosciences: Instrumentation and Applications [IG]
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last update: August 15, 2005
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