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Lookup NU author(s): Emeritus Professor Arthur Covington
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The definition of a "primary method of measurement" [1] has permitted a full consideration of the definition of primary standards for pH, determined by a primary method (cell without transference, Harried 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 system of measurement, the International System of Units (SI, Systeme International d'Unites). This approach has enabled resolution of the previous compromise IUPAC 1985 Recommendations [2]. Furthermore, incorporation of the uncertainties for the primary method, and for all subsequent measurements, permits the uncertainties for all procedures to be 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 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 degreesC. 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.
Author(s): Buck RP, Rodinini S, Covington AK, Baucke FGK, Brett CMA, Camoes MF, Milton MJT, Mussini T, Naumann R, Pratt KW, Spitzer P, Wilson GS
Publication type: Article
Publication status: Published
Journal: Pure and Applied Chemistry
Year: 2002
Volume: 74
Issue: 11
Pages: 2169-2200
ISSN (print): 0033-4545
ISSN (electronic): 1365-3075
Publisher: International Union of Pure and Applied Chemistry
URL: http://dx.doi.org/10.1351/pac200274112169
DOI: 10.1351/pac200274112169
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