Quinhydrone electrode

The quinhydrone electrode may be used to measure the hydrogen ion concentration (pH) of a solution containing an acidic substance.[1][2]

hydroquinone
quinone

A platinum wire electrode is immersed in a saturated aqueous solution of quinhydrone, in which there is the following equilibrium

C
6H
6O
2 ⇌ C
6H
4O
2 + 2H+ +2e−.

The potential difference between the platinum electrode and a reference electrode is dependent on the activity, , of hydrogen ions in the solution.

(Nernst equation)

The quinhydrone electrode provides an alternative to the most commonly used glass electrode.[3] however, it is not reliable above pH 8 and cannot be used with solutions that contain a strong oxidizing or reducing agent.[1]

References
  1. Bates, Roger G. Determination of pH: theory and practice. Wiley, 1973, pp 246-252
  2. Rossotti, F. J. C.; Rossotti, H. (1961). The Determination of Stability Constants. McGraw-Hill., p 135
  3. Vonau, W.; Guth, U (2006). "pH Monitoring: a review". Journal of Solid State Electrochemistry. 10 (9): 746–752. doi:10.1007/s10008-006-0120-4.
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