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. ofDurham, England in Spring 1998. An outline was proposed after agreementon, and resolution of the devisive issues contained in the 1985 CompromiseDocument on pH and pH Standards. An outline for the new pH Documentwas accepted at a second meeting of the Working Party, mainly afterremoval of possible topics, such non-aqueous solvent pH, and pH in biologicalmedia that were saved for later IUPAC documents or journal publications.The metrological concepts of traceability to SI units, and ranking ofmeasurement methods and materials according to statistical analysesof reproducibility and accuracy were the important new concepts notemphasized in the earlier document. Error analyses of liquid junctionpotential differences and ion size parameter variation in the Bates-Guggenheimconvention for activity coefficients were two of many new features ofthe work.
Early drafts of text and calculations for inclusion as Tables werediscussed at a third Meeting in Milan, Spring 1999. A public presentationof the draft document was given at the Berlin IUPAC Assembly in August1999 by Prof. S. Rondinini. Comments were received by members of theParty and used to prepare a modified new draft with input from mostWP Members. The resulting draft will be submitted to IUPAC relevantCommissions and Division Committee by the end of December 1999.
A final document is submitted to public review comments until 31 January2002 > see provisionalrecommendations
A review of the recommendations was prepared by F.G.K Baucke and publishedin Anal. Bioanal. Chem. (2002)374:772-777
> linkto abstract (Springer-Verlag website).