Report of the Working Party on
pH
The measurement of pH - Definitions,
Standards and Procedures
R.P. Buck (Chairman),
S. Rondinini (secretary), A.K. Covington (Editor), F.G.K. Baucke, M.F.
Camoes, M.J.T. Milton, T. Mussini, R. Naumann, K.W. Pratt, P. Spitzer,
G.S. Wilson
Abstract
The definition of a "primary method of measurement" (1) has permitted
a full consideration of the definition of primary standards of pH, determined
by a primary method (cell without transference, Harned cell), of the
definition of secondary standards by secondary methods, and of the question
whether pH, as a conventional quantity, can be incorporated within the
internationally-accepted SI system of measurements. This approach has
enabled resolution of the previous compromise IUPAC (1985) Recommendations
(2). Furthermore, incorporation of the uncertainties for all procedures
the linked to the primary standards by an unbroken chain of comparisons.
Thus a rational choice can be made by the analyst of the appropriate
procedure to adopt to achieve the target uncertainty of sample pH. Accordingly
this document explains IUPAC recommended definitions, procedures and
terminology relating to pH measurements in dilute aqueous solutions
in the temperature range 5-50 ºC. Details are given of the primary and
secondary methods for measuring pH and the rationale for the assignment
of pH values with appropriate uncertainties to selected primary and
secondary substances.
1. BIPM, Com. Cons. Quantitié de Matière 4 (1998).
2. A.K. Covington, R.G. Bates and R.A. Durst, Pure Appl. Chem.
57 (1985) 531.
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To Dr. S. Rondinini
E-mail: vertova@icil64.cilea.it
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