Clark electrode

The Clark electrode is an electrochemical sensor for determining the oxygen concentration in a solution (or in gas ). It was developed in 1962 by Leland Clark in Yellow Springs, Ohio.

Construction

The Clark electrode usually consists of a platinum cathode and a silver anode, which are connected via an electrolyte solution. However, other combinations such as gold to silver or gold from lead, form functional assemblies. From the measured material, these metal electrodes are usually separated by an oxygen-permeable membrane, usually made ​​of Teflon. There are also membrane-free arrangements in which the measured object at the same time serves as an electrolyte.

In the case of Pt / Ag combination is located on the platinum cathode to a bias voltage of -0.8 V versus the silver anode. (As it would for the electrolysis of the electrolyte solution used starting at 1.6 V, the bias voltage must not be in this order ). Other combinations, such as those of lead, not require polarization.

Now, the membrane is immersed to the measuring chamber in the measuring object (for example, in water or in an arterial blood sample ) for determination of the oxygen content, the O2 partial pressure in accordance with its diffuses through the membrane into the measuring chamber and there is reduced at the cathode. The cathode gives electrons to the oxygen, hydroxide ions (OH - ) are produced. At the anode, for example, silver is oxidized to silver ions and annealed in the presence of chloride as an insoluble AgCl crust to the electrode. The deposits of the oxidized anode metal must be removed regularly to get the unhindered Stromgängigkeit the measuring arrangement.

Thus, there is a current I, the partial pressure p ( O2) of oxygen O2 is directly proportional.

Upon further analysis of this resulting measured current is taken into account that both the rate of diffusion of oxygen through the membrane and the oxygen solubility in water is temperature dependent.

Applications

Spread the application is mostly in blood gas analyzers in intensive care for mechanically ventilated patients or as an adhesive electrodes in transcutaneous ( through the skin) measurement of blood gases, especially in newborns.

Commercial membrane-covered Clark electrodes are sold as oxygen meters. They are used in water monitoring, in the aquarium and in bioreactors. But there are also other applications, for example for the determination of biochemical oxygen demand of waste water as well as in food technology.