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Potentiometry measures electrochemical potential of charged particles using two electrodes and a potentiometer. A reference electrode with a fixed potential and an indicator electrode exposed to the analyte solution are used. The Nernst equation is used to calculate ion concentrations. pH meters are also used, and indicator electrodes can be metallic or membrane versions. Electrochemical properties of any substance can be determined from an electrochemical cell.
Potentiometry is a method used in electroanalytical chemistry to measure the electrochemical potential of charged particles. An electrode system is used to measure this potential and detect ions while other substances are also present. Two electrodes are placed in an analyte solution and connected to a potentiometer. Measurements are always made with no or low current, so the composition of the substance being measured is not altered, making quantitative analysis possible.
In a potentiometer-connected electrochemical cell, a reference electrode is used which has a potential independent of any temperature variable or analyte. The electrodes used as a reference in potentiometry usually include hydrogen, saturated calomel, or silver chloride. An indicator electrode is exposed to the analyte solution and its potential varies depending on the ions present in the solution. Each electrode is placed in a separate solution and connected to a single potentiometer instrument, while a salt bridge is exposed to each sample, completing an electrical circuit.
The purpose of measurements with electrochemical cells is to calculate ion concentrations using the electrode potential, the universal gas constant, Faraday’s constant, the charge of the ions, and the temperature in Kelvin. Variables and constants are used to determine the potential of a substance using the Nernst equation, first created in the late 1800s. In the early 1900s, it was discovered that the potential could be different on each side of a membrane of glass if the hydronium ion concentrations varied from side to side.
Instruments used in potentiometry also include pH meters. pH defines whether a substance is an acid, a base, or a neutral, which can greatly affect potentiometry measurements. In an electrochemical cell, a reference electrode, called anode, has a potential independent of any temperature variable or analyte. An indicator electrode, often referred to as a cathode, is exposed to the analyte solution and its potential varies depending on the ions present in the solution.
Indicator electrodes can be metallic or membrane versions, also called ion-selective electrodes. The potentiometer is used to make measurements of low resistance circuits. For use with high resistance glass electrodes, pH meters are suitable for making electrochemical measurements of low and high resistance circuits. A pH electrode must be immersed in water to work and has an important purpose in potentiometry. Under the right conditions, the electrochemical properties of any substance can be determined from an electrochemical cell.
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