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PTB Seminar on the international comparability of pH value measurements


As a measure of the acid or alkaline quality of a solution, the pH value is an important measurand as, among other things, in process technology, medicine and environmental protection. The measurement of the pH value also serves to control and regulate biological and chemical processes.

It is decisive for the comparability of pH value measurements to be ensured that the reference materials used for calibrating pH value measuring facilities are traced back to national measurement standards, i.e., in this, case, to primary pH value reference materials.

The pH values of a number of primary pH value reference materials are determined at the PTB and at other national metrology institutes with the aid of a sophisticated electrochemical measuring procedure. These pH values form the fixed points of a practical scale of pH values on which all pH value measuring procedures are based.
The scale for pH values realized by the PTB is disseminated to laboratories of the German Calibration Service, which in turn link up to it pH value reference materials which they disseminate to the users. In Germany, the traceability of all pH value measurements is thus assured.

Within the scope of EUROMET (European Collaboration in Measurements Standards) projects, the scale of pH values is compared in different points with a view to achieving uniformity of the pH value measurements in Europe. Eight laboratories from seven European countries take part in comparison measurements coordinated by the PTB. Within the scope of a first project, agreement could be reached within an uncertainty of measurement of the pH value of delta(pH) = 0,003.

On September 23 and 24, 1996, the PTB held an international seminar in which experts from industry, universities and metrology institutes took part. Apart from the results of the comparison measurements, approaches to establishing a uniform and metrologically based pH value scale, which has not yet been realized on the international level, were discussed.

More detailed information can be obtained from:
Petra Spitzer, PTB
tel. 0531-592-3322 or 3301
or in the Internet under News · Current events.