Milton, M J T (2000) pH measurements by a primary method. In: Metrologia 2000, December 2000, Sao Paulo.

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Abstract

The results of measurements made by primary methods are directly traceable to the SI. A recent review by IUPAC of the international guidelines on the measurement of pH has concluded that measurements made with a hydrogen electrode in a Harned Cell fulfil the criteria to be primary. This important development anchors pH measurements within the metrological framework of the SI.

An important consequence of this approach is that it is now possible for new buffer systems to be evaluated against objective criteria required for them to be primary.

Primary pH measurements made with the Harned Cell are estimated to have an uncertainty of ±0.004. The major contributions to this uncertainty is due to the measurement of the molality of HCl and the variability in the Ag/AgCl electrodes. The optimisation of both of these factors leads to some important principles in the operation of Harned Cells. The uncertainty is increased by approximately a factor of ten for pH measurements at the secondary level.

Item Type:	Conference or Workshop Item (UNSPECIFIED)
Subjects:	Analytical Science
Last Modified:	02 Feb 2018 13:17
URI:	https://eprintspublications.npl.co.uk/id/eprint/2281