Ion selective electrodes

Ion selective electrodes are electrodes which respond to a wide range of selected ions. Glass electrode which measures hydrogen ion activity is an example. pH meters are used here to determine water purity. According to the ion species to be determined, glass membrane composition has to be changed. By this method, we can measure sodium, silver, potassium, ammonia and other univalent cations. The membrane is either a single crystal or a compacted disc in solid state electrodes. This membrane effectively isolates the reference solution from the solution under measurement. In fluoride ion measurement, lanthanum fluoride is used as membrane of solid state electrodes. In sulphide ion measurement, silver sulphide membrane is employed. There exists one more category of electrodes- heterogeneous membrane electrodes. These electrodes are similar to the solid state electrodes differing in one aspect-active material being dispersed in an inert matrix. In the latest version- liquid-ion exchange electrode, reference solution and the solution to be measured are separated by a porous layer containing an organic liquid of low water solubility.