Quinhydrone Electrode. The quinhydrone electrode is one of the less common measuring electrodes and operates best over the pH range between 1,0 and 8.0.The system is operated in the following way. An equimolecular mixture of hydroquinone and p-benzoquinone are added to the sample solution and a pH dependent oxidation-reduction couple is formed between quinone and quinol, the potential being measured with a platinum electrode against another standard electrode. In more alkaline environments than pH 8.0, the quinhydrone is readily oxidized and, thus, the ionization system becomes unstable.

Further Information on this Topic can be found in the books of R.P.W. Scott by following the listed links