pH electrodes and ORP electrodes are analytical sensors for measuring pH and oxidation-reduction potential (ORP). These electrodes can be for measuring either pH or ORP, or both. pH is the negative logarithm of the hydrogen ion activity in solution. The pH value of a substance is directly related to the ratio of the hydrogen ion [H+] and the hydroxyl ion [OH-] concentrations. It is one of the most common laboratory measurements because many chemical processes are dependent on pH. Oxidation-reduction is a type of chemical reaction in which electrons are transferred from one substance to another. The oxidized species loses electrons and the reduced species gains electrons. Both species must be present for the reaction to occur.

Important specifications for pH electrodes and ORP electrodes are measuring ranges and accuracies, as well as response time, which is typically given as time to reach 95% of final value. pH electrodes and ORP electrodes are available as either single cells or combination cells. Single cells, one part of an electrode pair, require separate reference electrode and are the best choice for colloidal suspensions, iodides in sample, and high percentage of solids in fluid. Combination electrodes are composed of two parts, the measuring electrode and the reference electrode. This is the most common configuration and is best for laboratory or field applications.

pH electrodes and ORP electrodes are analytical sensors for measuring pH and oxidation-reduction potential (ORP). These electrodes can be for measuring either pH or ORP, or both. pH is the negative logarithm of the hydrogen ion activity in solution. The pH value of a substance is directly related to the ratio of the hydrogen ion [H+] and the hydroxyl ion [OH-] concentrations. It is one of the most common laboratory measurements because many chemical processes are dependent on pH. Oxidation-reduction is a type of chemical reaction in which electrons are transferred from one substance to another. The oxidized species loses electrons and the reduced species gains electrons. Both species must be present for the reaction to occur.

Important specifications for pH electrodes and ORP electrodes are measuring ranges and accuracies, as well as response time, which is typically given as time to reach 95% of final value. pH electrodes and ORP electrodes are available as either single cells or combination cells. Single cells, one part of an electrode pair, require separate reference electrode and are the best choice for colloidal suspensions, iodides in sample, and high percentage of solids in fluid. Combination electrodes are composed of two parts, the measuring electrode and the reference electrode. This is the most common configuration and is best for laboratory or field applications.

Reference electrodes can be either refillable or sealed. The trade-off between the two is amount of maintenance versus length of product life. Refillable electrodes obviously need more maintenance, but also last longer and typically have higher accuracies. Sealed electrodes, while not requiring refilling, have a limited life, as the chemicals inside get used up and not replaceable.

Two types of reference cell junctions are common. Single junction reference electrodes contain a single electrolyte. The electrolyte provides a constant level of the ion sensed by the reversible reference element and forms a low potential liquid junction with the sample solution. Double junction reference electrodes have an additional reference cell in front of the potassium chloride cell, which screens the sample from the potassium chloride reference cell.  Double junction cells typically have a longer time response.

Handheld or portable configurations allow pH electrodes and ORP electrodes to be used with ease in laboratories, where the operator may be testing several different samples. Insertion style electrodes are often inserted into process piping through a tapped hole in a pipe or bulkhead. Flow-through styles fit directly into the pipeline and become an integral part of it via some connection such as flanges or other fittings.

Typical features of pH electrodes and ORP electrodes include temperature compensation, built-in temperature sensor, submersible or water resistant design and a design specially suited for food or sanitary applications.