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

Area of Science:

• Electrochemistry
• Metrology

Background:

• The unified pH ([Formula: see text]) concept allows for precise pH measurements in non-aqueous and mixed media, ensuring comparability with the traditional aqueous pH scale.
• Practical implementation of the unified pH concept is limited by a lack of established reference values.

Purpose of the Study:

• To address the shortage of reference values for the unified pH scale.
• To assign the first reference [Formula: see text] values through an interlaboratory comparison.
• To demonstrate the robustness of unified pH measurements using different experimental setups.

Main Methods:

• An interlaboratory comparison was conducted by expert electrochemistry laboratories under the EMPIR UnipHied project.
• Phosphate buffer in a water-ethanol mixture (50 wt% ethanol) and ammonium formate buffer in pure ethanol were used as test solutions.
• Extensive statistical treatment of reported measurement data was employed to assign reference values.

Main Results:

• The first reference [Formula: see text] values were assigned for specific buffer solutions in non-aqueous media.
• Two distinct measurement setups, including one suitable for industrial use, were utilized, confirming measurement robustness.
• The study successfully demonstrated the feasibility of establishing a unified pH scale.

Conclusions:

• This work represents a significant advancement towards the practical adoption of the unified pH concept.
• The established reference values and demonstrated robustness pave the way for applications in fields like liquid chromatography, biofuels analysis, and electrocatalysis.