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Analytical Chemistry Division (V)
Physical and Biophysical Chemistry Division (I)
Chemistry and the Environment Division (VI)


Number: 2004-005-2-500

Title: Comparable pH measurements by metrological traceability

Series Titles: pH Measurements in Complex Matrices
Part I - pH Measurements in water quality monitoring and assessment Part II- pH Measurements of clinical, biochemical and environmental relevance

Task Group
M. F. Camoes

Members: Peter Atkins, Arthur Covington, Paul de Bievre, Bjarne Kristensend, Erno Lindner, Gunther Meinrath, Martin Milton, Kenneth Pratt, Sandra Rondinini, Petra Spitzer, David Turner, Yoshio Umezawa, and George Wilson

- To implement traceability chains for pH values in routine measurements in order to achieve target uncertainties for specific applications.

- To develop educational and quality control tools for reference and testing laboratories under the observation of chemical and metrological principles.

- To improve the comparability and the assessment of pH values.

The most often measured chemical parameter, pH, has driven the awareness of scientists and decision makers to the need for reliable analytical results. Its unique feature of being defined in terms of a single ion activity, the multiplicity of practical steps and assumptions involved in the assessment of pH values for primary reference buffer solutions and the diversity of secondary methods, give a slight overview of the multidisciplinarity of the subject with multifold implications. After the production of the IUPAC paper "The Measurement of pH. Definitions, Standards, and Procedures (IUPAC Recommendations 2002)", Pure Appl. Chem. 74, 2169-2200 (2002), a workshop "Importance of Traceable pH Measurements in Science and Technology conducted at PTB/Braunschweig, Germany, in September 2001, organized and promoted by members of this Project's Task Group, with a wide range of participants, revealed priorities and showed a strong request from the concerned community for continuing action of the task group, on

- Educational efforts on the calculation of the uncertainty of pH values;

- Elaboration of recommended protocols for specific applications (e.g. quality monitoring and assessment in the different applications of water and in physiological media) by round robin studies, observing the traceability chain, calculating the uncertainty of the sample pH;

- Critical assessment of the existing methods to calculate the hydrogen ion activities and concentrations, allowing extension of the presently adopted model for a wider range of applications.

The proposal aims at covering these objectives. Work is progressing in the frame of the group's research activities and will be submitted to IUPAC for endorsement.

> link to former project of the on the Definition of pH Scales (#551/1/97)

The Task Group Chair has published in February 2005 the following paper of relevance to this project: 'Reassessment of pH Reference Values with Improved Methodology for the Evaluation of Ionic Strength', M. J. Guiomar H.M.Lito and M. Filomena G.F.C. Camões, Anal. Chim. Acta, 531, 2005,141-146 [doi:10.1016/j.aca.2004.09.048]

The task group met in October 2005 and in April 2006.

> May 2006 report update (pdf file - 36KB)

> Jan 2007 - completion of related project 2004-016-2-500, titled 'Guidelines for potentiometric measurements in suspensions'

> July 2007 report update (pdf file - 45KB)


Last Update: 16 October 2007

<project announcement published in Chem. Int. May/Jun 2005>

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Page last modified 16 October 2007.
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