Symmetric Potentiometric Cells for the Measurement of Unified pH Values

Recently the UnipHied consortium published a new article – Symmetric Potentiometric Cells for the Measurement of Unified pH Values. Symmetry 2020, 12, 1150, where we compared the performance of different cells and instruments used to measure acidities on the unified pH scale (pHabs). The advantage of the unified pH scale is that it enables expressing the acidities of any systems – non-aqueous, solutions, colloidal systems, etc – via pHabsH2O values, which are directly comparable to the conventional pH values of the aqueous pH scale.

This is the first time unified acidities have been measured outside of our group. Nine partners from Europe – national metrology institutes and universities – have set up systems to measure pHabs and validated them with standard aqueous buffers.

The results show that the method is robust and does not depend on the cell nor the instrument (pH meter, potentiostat, or electrometer). The inherent symmetry of the cell design helps to reduce the experimental workload and improve the accuracy of the obtained results.

The next step is to measure unified acidities of non-aqueous systems, which could be used by routine laboratories to calibrate their pH electrodes.

The UnipHied project is funded from the EMPIR programme (project 17FUN09) co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

Our acid-base research at 19th European Symposium on Fluorine Chemistry 2019

On 26.08.19 at 19th European Symposium on Fluorine Chemistry 2019 Ivo Leito gave a talk Acidities of molecules and media: the united pKa-pHabs scale in 1,2-dichloroethane.

For the first time in a low-polarity solvent, the scale has a dual nature, being both a pKa scale of the involved acids (i.e. describing acidity of molecules) and at the same time a pH scale, describing the acidity of the solutions (media).

The scale spans 28 orders of magnitude (pH or pKa units) and is composed of 87 acids of diverse nature. The scale is linked to the unified acidity (pHabs) scale and expressed in values, which makes the acidities of the solutions directly comparable to the conventional aqueous pH scale. This in turn makes the scale a useful tool in future studies of acid-driven processes (reaction mechanisms, catalysis, strong oxidants, etc) in low-polarity media.

This work has been published in: Chem. Sci., 2017, 8, 6964-6973. A unified view to Brønsted acidity scales: do we need solvated protons?.

It is part of a larger endeavor – to promote a wider usage the unified pH scale by the research and technology communities, which is currently in progress via the UnipHied. The project is funded from the EMPIR programme (project 17FUN09) co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.