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. **************************************************************** Delta Isotopes Consultancy Dr. Pier A. de Groot Pastoor Moorkensstraat 16 2400 Mol - Achterbos Belgium Tel. +32 (0)14 326 205 e-mail: [log in to unmask] or [log in to unmask] Associate editor for stable isotopes of eEarth on-line magazine http://www.electronic-earth.net Organizer of the Isotope Programme at the: EGU2007 General Assemblee (Vienna, Austria, 15-20 April) The programme can be found at: http://meetings.copernicus.org/egu2007 (Click at: Programme > Call-for-Papers/Abstract Submission) Isotopes in Geosciences: Instrumentation and Applications [IG] Visit my WEB-site about my ³Handbook of Stable Isotope Analytical Techniques², with a link to the Elsevier web site on the handbook (marked: ŒOrder Now¹): http://users.pandora.be/handbook/index.html last update: August 15, 2005 Volume I is now available. Volume II is expected to be available in 2007. **************************************************************** Why we are searching for extraterrestrial intelligence While we lack it so much on Earth? ****************************************************************