What is a Polarographic Dissolved Oxygen Sensor?

A polarographic sensor is commonly used to determine the dissolved oxygen concentration in a liquid. The dissolved oxygen will be reduced at the surface of a noble metal electrode, the working electrode, acting as a cathode:

O₂ + 2 H₂O + 4 e^– → 4 OH^–

A silver/silver chloride counter electrode, the anode, releases the required electrons:

4 Ag → 4 Ag⁺ + 4 e^–

This electron flow from the anode to the cathode represents the measuring signal which is proportional to the partial pressure of oxygen in the measured solution.

The above decribed chemical reaction does not start automatically, but has to be imposed by an applied voltage which has to have at least the magnitude of the standard redox potential (+401 mV) of the reaction at the cathode, but with reversed polarity. This negative voltage, the polarisation voltage, must be absolute constant and has to be stabilized against a reference electrode. 

Explore our range of dissolved oxygen sensors.