Results of Pilot Comparisons of National Standards for the Activity of Hydrogen Ions in Aqueous Solutions

The enormous need for support of measurements of the hydrogen index (pH) in various branches of industry and the national economy of Russia make measurement of pH one of the most important methods for monitoring aqueous media. In 2013 work was carried out to introduce into the State Register of Means of Measurement of the Russian Federation a buffer solution and titration standard with a pH value of 7.00, a 2nd order working standard for pH which is one of the nonstandard solutions most in demand for verification and calibration of instruments for measuring pH. The metrological characteristics of the 2nd order working standard for pH have been confirmed in pilot comparisons through COOMET (COOMET project 655/RU/15). The results of a pilot comparison for determination of the pH of a phosphate buffer solution with pH=7.00 are presented here. 8 metrological institutes and 10 metrological organizations took part in the comparisons. The results showed that the overwhelming majority of the participants in the comparisons obtained results for the pH measurements with an uncertainty that did not exceed ±0.03 of the average value, which is an acceptable criterion for pH measurements.