National standard of PH quantity

Name of Standard: National standard of pH quantity

Code: ECM 350-1/14-057

Year of publication: 2014

Department: dpt. 6016 CMI RI Brno

Garant: Mgr. Matilda Roziková, Ph.D.

Number of CMC lines provided: 6

The pH value is defined as the negative value of the decimal logarithm of the activity of hydrogen ions in a diluted aqueous solution (I ≤ 0.1 mol.kg^-1). Since pH is defined by quantities that cannot be measured by independent methods, the above-mentioned definition can be considered only theoretical. In order to be able to determine the pH of a solution, it is necessary to adopt a primary measurement method with all dependencies of the measured quantities and with uncertainties that include all limitations (Bates – Guggenheim convention).

For the implementation of the primary pH standard, a solution based on the principle of a cell without transference (without diffusion potential) with a standard hydrogen electrode and reference silver/silver chloride electrode, the so-called Harned cell, was chosen. There was no commercially available solution. The design and implementation of standard of pH quantity took place in 1999-2013.

The main role of pH primary metrology is to provide a pH quantity with traceability to SI units and transfer it to primary certified reference materials, secondary standard, secondary certified reference materials, reference materials used for calibration of pH electrodes, working standards and working gauges, in the range of 1.67 to 12.81 pH units and accuracies according to the needs of industry and other users in the Czech Republic.

The state standard of pH quantity consists of the following parts:

Basic metrological characteristics: