Analytical instruments

Process analyzers

Environmental/Process analyzers

Oxidation-Reduction Potential (ORP) Measurement

When a non-erosive electrode, such as a platinum electrode, is immersed in an oxidation-reduction solution, electric potential difference is generated between the surface of the electrode and the solution. This is called the Oxidation-reduction Potential, or Eh, and is indicated by the following formula.

[Ox] Activity of the oxidizer
[Red] Activity of the reducer
E0 The ORP when [Ox] equals [Red] is called the standard potential, which is particular to a specific oxidation-reduction solution at a specific temperature.
F Faraday constant

As shown in the above formula, the absolute value of Eh cannot be calculated, thus Eh is calculated based on a standard hydrogen electrode with a standard potential of zero. However, a hydrogen electrode has a complex construction, and thus a reference electrode is more commonly used.