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
Chairman: 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
Objective:
- 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.
Description:
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)
Progress:
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>
