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Analytical Chemistry Division (V)

Working Party on the Definition of pH Scales

Number: 551/1/97

Title: The measurement of pH. Definition, standards and procedures (revised title)

Coordinator(s): R. Buck - Access to list of members

Remarks: Joint project of Division I and V

Completion Date: 2002 - project completed

Over the years, the subject has been of controversy since the IUPAC Recommendations made in 1985 that left two "definitions" of pH as acceptable (ref.1). In 1997, a proposal was made to initiate a new working party to develop a single definition of pH.

Ref.1. Pure Appl. Chem. 57(3), 531-542 (1985)

The program formally began with a working Meeting at the Univ. of Durham, England in Spring 1998. An outline was proposed after agreement on, and resolution of the devisive issues contained in the 1985 Compromise Document on pH and pH Standards. An outline for the new pH Document was accepted at a second meeting of the Working Party, mainly after removal of possible topics, such non-aqueous solvent pH, and pH in biological media that were saved for later IUPAC documents or journal publications. The metrological concepts of traceability to SI units, and ranking of measurement methods and materials according to statistical analyses of reproducibility and accuracy were the important new concepts not emphasized in the earlier document. Error analyses of liquid junction potential differences and ion size parameter variation in the Bates-Guggenheim convention for activity coefficients were two of many new features of the work.

Early drafts of text and calculations for inclusion as Tables were discussed at a third Meeting in Milan, Spring 1999. A public presentation of the draft document was given at the Berlin IUPAC Assembly in August 1999 by Prof. S. Rondinini. Comments were received by members of the Party and used to prepare a modified new draft with input from most WP Members. The resulting draft will be submitted to IUPAC relevant Commissions and Division Committee by the end of December 1999.

A final document is submitted to public review comments until 31 January 2002 > see provisional recommendations

Project completed - IUPAC Recommendations 2002 published in Pure Appl. Chem. 74(11), 2169-2200, 2002.

A review of the recommendations was prepared by F.G.K Baucke and published in Anal. Bioanal. Chem. (2002)374:772-777
> link to abstract (Springer-Verlag website).

Another review was published in Chem. Int. in the July 2003 issue.

Last Update: 1 July 2003


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