On April 16, 2024, prof. Ivo Leito presented the topic of “Unified pH Scale – from Concept to Applications” at the 8th Baltic Electrochemistry Conference: Finding New Inspiration 2 (BEChem 2024), held in Tartu, Estonia. 

At the beginning of the presentation, Ivo gave a brief overview of why pH, a widely used value for expressing acidity, has serious limitations. Thus, it cannot be used to compare the acidities of solutions in different solvents, which can hinder the understanding of chemical, biological, environmental, and industrial processes.

A much more practical approach could be the usage of an absolute/universal pH, which would allow the comparison of acidities in different solvents. Thus, the main part of the presentation was focused on the theoretical and practical aspects of unified pH (pH_abs). In recent years, our Acid-base Studies workgroup in the Analytical Chemistry Chair has worked extensively with the development and measurement of unified pH values for various systems in different solvents (liquid chromatography modile phases, electrocatalytic mixtures, strongly acidic solutions, etc). A differential potentiometry method for pH_abs has been developed in the workgroup to obtain the unified pH values and has been now distributed to a number of groups in Europe in the framework of the UnipHied project.

For now, the unified pH has matured from a concept into a practical tool and has been accepted both by the European metrology community (Euramet) and by IUPAC. The unified pH could be utilized in various applications, such as liquid chromatography, catalytic systems, and acidity at the interfaces between phases. 

The presented research is largely the result of the EMPIR programme project 17FUN09 “UnipHied”.