Ion selective electrodes (ISEs) are part of group of relatively simple and inexpensive analytical tools which are commonly referred to as sensors. The pH electrode is the most well known and simplest member of this group and can be used to illustrate the basic principles of ion selective electrodes [1]. Also, ISE is a transducer sensor which converts the activity of a specific ion dissolved in solution into an electrical potential which can be measured by a voltmeter or pH meter. The sensing part of the electrode is usually made as an ion specific membrane, along with a reference electrode. It is impossible to measure the interfacial potential directly, but this can be achieved using a suitable electrochemical cell and the potential is measured at equilibrium under a zero current condition [2].
