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]. 1-2-Ion selective electrode cell measurements:- The cell consists of both an indicator and reference electrode. Since the potential of the reference electrode is constant, the potential developed at the indicator electrode that contains information about the amount (activity) of analyte in a sample. An electrochemical sensor based on a thin selective membrane or film as recognition element is an electrochemical half-cell equivalent to other half-cells of the zeroth (inert metal in a redox electrolyte). The components of electrochemical cell are shown in Figure 1-1. The potential developed at the membrane is the result of either an ion exchange process or an ion transport process occurring at each interface between the membrane and solution.