The “pH-window” of a representative deep eutectic solvent and evaluation of electrodes for pH measurement

The Brønsted acid–base properties of ethaline, composed of choline chloride and ethylene glycol, were investigated as a representative deep eutectic solvent (DES). Rigorous potentiometric titrations with a hydrogen electrode were performed for the first time in DES to determine the autoprotolysis constant and the p K a values of some weak acids. These results revealed a ~ 4 unit shift in pH relative to water and established the pH window of the DES, which allows direct conversion of the pH value between the DES and conventional solvents. IS-FET and glass electrodes were also evaluated, confirming practical applicability. • Rigorous pH measurements in DES “ethaline” using a hydrogen electrode. • The autoprotolysis constant and a wide range of p K a values were determined. • The pH-window of the model DES mapped onto the water-based pH scale. • Thermodynamics-based Brønsted acid-base profiling of a DES for the first time. • IS-FET and glass electrodes were evaluated for practical pH measurement.