Redoxpotential

Redox potential, also known as oxidation–reduction potential (ORP), is a measure of the tendency of a chemical environment to gain electrons and be reduced. It reflects the overall redox state of a system and is typically expressed in volts (V) or millivolts (mV). The value is established by the balance of oxidized and reduced species present and is measured with a redox electrode against a reference electrode.

For a specific redox couple, the potential is related to the concentrations of oxidized and reduced forms by the Nernst equation. Under standard conditions (298 K, 1 atm, activities of 1), the standard redox potential E° is defined relative to the standard hydrogen electrode (SHE). In real samples, the measured potential depends on pH, mediator species, and the presence of other redox couples, so E is not fixed for a given pair.

Measurement and interpretation: ORP readings come from redox electrodes, often paired with a reference electrode such as Ag/AgCl. Since most samples contain many redox-active species, the observed ORP is an aggregate signal rather than a single couple’s potential; hence, interpretation requires knowledge of the sample composition, buffering, and temperature.

Applications: ORP is used in water treatment, environmental monitoring, food and beverage processing, corrosion science, and biology to assess oxidative stress, disinfection effectiveness, and overall redox balance. In biological systems, redox potential reflects the balance of cofactors such as NAD+/NADH and glutathione (GSSG/GSH), influencing metabolism and signaling.

Limitations: ORP readings are influenced by pH, temperature, electrode condition, and the presence of complex mixtures, and they do not identify which species govern the redox state. They provide a general indication of oxidative capacity rather than a precise map of redox couples.