Rigorous pH measurement in non-aqueous solution: measurement method and reference values in ethanol

The recently introduced unified pH (pHabsH2O) concept enables rigorous pH measurements in non-aqueous and mixed media while at the same time maintaining comparability to the conventional aqueous pH scale. However, its practical application is hindered by a shortage of reference pHabsH2O values. In order to improve this situation, the European Metrology Research Project (EMPIR) UnipHied (“Realisation of a UnipHied pH scale”) launched an interlaboratory comparison among highly experienced electrochemistry expert laboratories to assign the first such reference pHabsH2O values by adopting an extensive statistical treatment of the reported measurement data: to phosphate buffer in water–ethanol mixture (50 wt% of ethanol) and ammonium formate buffer in pure ethanol. Two different measurement setups — one capable of being easily adopted in industrial applications — have been used to demonstrate the robustness of pHabsH2O measurement. This is an important step towards wider adoption of the pHabsH2O concept in practice, like liquid chromatography, biofuels analysis and electrocatalysis.