Redox potential
The redox potential is used to reflect the macroscopic redox behavior of all substances in an aqueous solution. The higher the oxidation-reduction potential, the stronger the oxidability. The lower the oxidation-reduction potential, the stronger the reducibility. A positive potential indicates that the solution exhibits a certain degree of oxidation, while a negative potential indicates that the solution exhibits a certain degree of reduction.
The oxidation-reduction potential (ORP) is a parameter that characterizes the amount of oxidizing and reducing substances in water. The redox potential is generally measured in millivolts (mv). When the redox potential is positive, it indicates the presence of oxidizing substances in the water. When the redox potential is negative, it indicates the presence of reducing substances in the water. We often use ORP instruments instead of residual chlorine meters to reflect whether the residual chlorine in the reverse osmosis influent is qualified, and the specific values vary for different systems and situations. For RO membranes, there is no problem in a partial reducing environment because the protective solution of the membrane product itself is a reducing solution. However, the redox potential cannot be a small negative value, as it is prone to the generation of spoilage anaerobic bacteria and microorganisms.
Why should we measure the redox potential
For a water body, there are often multiple redox potentials, forming a complex redox system. And its oxidation-reduction potential is the comprehensive result of the oxidation-reduction reaction between various oxidizing and reducing substances. Although this indicator cannot be used as an indicator of the concentration of certain oxidizing and reducing substances, it helps to understand the electrochemical characteristics of water bodies and analyze their properties, making it a comprehensive indicator.
Method for measuring redox potential
Using a platinum electrode as the indicator electrode, a saturated calomel electrode as the reference electrode, and a water sample to form a primary battery. Measure the redox potential of the platinum electrode relative to the saturated calomel electrode using an electronic millivoltmeter or universal pH meter, and then convert it into the redox potential relative to the standard hydrogen electrode as the reported result.
Calculation formula: Ψ N= Ψ Ind+ Ψ Ref
In the equation:
Ψ N – Oxidation-reduction potential of the tested water sample, mV;
Ψ Ind – measured redox potential of the water sample, mV;
Ψ Ref – Measure the electrode potential of a saturated calomel electrode at temperature, mV, which can be found in the physical chemistry manual.
Note
The redox potential of water bodies must be measured on-site.
The redox potential is influenced by factors such as solution temperature, pH, and chemical reaction reversibility.
The redox potential is related to the oxygen partial pressure and also influenced by pH. When the pH is low, the redox potential is high; when the pH is high, the redox potential is low.