Clark electrode

thumb|A schematic representation of Clark's 1962 invention, the oxygen electrode

The Clark electrode is an electrode that measures ambient oxygen partial pressure in a liquid using a catalytic platinum surface according to the net reaction:

: O₂ + 4 e⁻ + 4 H⁺ → 2 H₂O

It improves upon a bare platinum electrode by using a semipermeable membrane to reduce fouling and metal plating onto the platinum.

History

Leland Clark (Professor of Chemistry, Antioch College, Yellow Springs, Ohio, and Fels Research Institute, Yellow Springs, Ohio) had developed the first bubble oxygenator for use in cardiac surgery. However, when he came to publish his results, his article was refused by the editor since the oxygen tension in the blood coming out from the device could not be measured. This motivated Clark to develop the oxygen electrode.

The electrode, when implanted in vivo, will reduce oxygen and thus requires stirring to maintain the chemical equilibrium with the environment. Severinghaus improved the design by adding a stirred cuvette in a thermostat. A discrepancy between the measured partial pressure of oxygen (pO₂) between blood samples and gaseous mixtures of identical pO₂ meant that the modified electrode required calibration; consequently, a microtonometer was added to the water thermostat.

This sensor used a single Clark oxygen electrode coupled with a counter electrode. As with the Clark electrode, a permselective membrane covers the Pt electrode. Now, however, the membrane is impregnated with immobilized glucose oxidase (GOx). The GOx will consume some of the oxygen as it diffuses towards the Pt electrode, incorporating it into H₂O₂ and gluconic acid.