Working Party on the Definition of pH Scales
Title: The measurement of pH. Definition, standards and procedures
Buck - Access to list of
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),
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
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
Project completed - IUPAC Recommendations 2002 published
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
to abstract (Springer-Verlag website).
Another review was published in Chem.
the July 2003 issue.
Last Update: 1 July 2003