The Quinhydrone Electrode

The quinhydrone electrode is a less common measuring electrode that operates best over the pH range between 1,0 and 8.0. In more alkaline environments the quinhydrone is readily oxidized and, thus, the ionization system becomes unstable. 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. By employing solutions of known pH (e.g. buffers of pH 4 and pH 7, which provide emf’s of 265 mv and 90 mv respectively) the quinhydrone electrode is sometimes used to calibrate other reference electrodes.