The physical chemistry primary traceability at CMI

This article describes the actual achievements in the field of physical chemistry and introduces the methods of traceability used in the Department of Primary Metrology of Physical Chemistry in the fields of electrolytic conductivity, pH and coulometry. The Department of Primary Metrology of Physical Chemistry is located in Brno, the second largest city of the Czech Republic. The basic theory and the construction of the primary measurement standard of electrolytic conductivity is described. The primary conductometric cell consists of three parts. The length parameters of the most important middle part are precisely measured. The original conductometric cell was modified to reduce the volume of the measured liquid. The measurement standard participated in key comparisons with further publishing results in KCDB and in 2018 it was established as the state measurement standard of electrolytic conductivity in the range (0.005‒10) S‧m ‒1 . In 1999, the construction of the primary pH measurement standard began. The primary measurement standard consisted of five Harned cells without transfer. The challenge was the design of Harned cells. In 2005, a new, simpler design of Harned cells was used. After determining the standard potential of the five reference electrodes, the acidity function of the buffer is determined. The measurement standard participated in key comparisons with further publishing results in KCDB and in 2014 it was established as the state pH measurement standard. The Czech Metrology Institute is also a producer of certified reference materials for pH and electrolytic conductivity. It was accredited by the Czech Institute for Accreditation according to the EN/ISO 17034 standard in 2015. In 2015, the new primary measurement standard for substance quantities was put into operation. Coulometry as a primary method is used to realise and transfer the unit of substance through primary reference materials. In 2019, it successfully participated in the key comparison CCQM-K73.2018. It is planned to establish the primary measurement standard for the quantity of substances as a state measurement standard in the near future.