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International Journal Of Applied Research In Science And Engineering ISSN (Online): 2456-124X International Conference on Emerging Technologies in Engineering, Biomedical, Medical and Science (ETEBMS - November 2016) PRINCIPLE AND APPLICATIONS OF ION SELECTIVE ELECTRODES-AN OVERVIEW Vishal Arun Naik M.Sc. Organic Chemistry, Mahatma Phule Arts, Science & Commerce College, Panvel Mumbai University Abstract: on selective electrodes are used for the detection of a particular ion owing to its selectivity arising from the type of ionophore used. In this paper we propsed the principal, selectivity and applications of ion selective electrodes along with the advantages and limitations. I. INTRODUCTION ELECTROANALYTICAL techniques deal with the measurement of electrical quantities such as current, potential or charge and their relation towards chemical parameters. The birth of bio-electrochemistry took place 200 years ago (1791) in Bologna, Italy, where Luigi Aloisio Galvani was dissecting a frog.1 He discovered that the legs of the dead frog twitched when struck with electricity. Most of this field was concerned with the study of changes in chemical reactions caused by passing electrical current through the reaction mixture and the production of electrical energy by chemical reactions. Electrochemical reactions take place in the liquid-electrode interface in contrast to chemical reactions that occur in bulk solutions. At least two electrodes (conductors) and a sample (electrolyte) solution is required for these techniques, which constitute the electrochemical cell (Fig. 1). The electrode that responds to the target electrode is the indicator (or working) electrode and the other electrode is termed as the reference electrode which is at a constant potential (independent of the properties of the solution). Figure 1: Representation of an electrochemical cell for the measurement of potential. Potentiometry is an important technique in electroanalysis, which gives information about the sample composition by measuring the potential established across a membrane. Different types of membranes are produced with different ion recognition materials to increase the selectivity and sensitivity. These electrodes are used for decades for the detection of various ionic species like hydrogen, potassium, calcium, and fluoride in complex samples. In contrary, potentiostatic technique deals with the study of charge transfer at the liquidelectrode interface. Here the electrode potential is used to derive an electron transfer reaction, and the resultant current is measured. Electroanalysis can be carried out only when the medium between the two electrodes is conducting.2 These techniques offer low detection limit, high sensitivity, large linear dynamic range, precision and accuracy with a low cost instrumentation. There are a number of important benefits associated with the use of electroanalytical techniques:3 Selectivity and specificity. Low detection limit with high sensitivity. Choice of electrode material. Results are real time or near real time. Miniaturization of the sensors. ISEs are capable of selectively measuring a particular ionic species. These electrodes are classified as membrane electrodes containing an ion permissible membrane that separates the sample from the internals of the electrode. The main advantage of using ISEs are that they are insensitive to colour, viscosity or suspended solids. They are also tolerant to small changes in pH.4 Response time and reversibility are critical for the performance of this sensor. The problem of reversibility considering all electrochemical processes as equilibrium processes are the contribution of Nernst. Nernst equation states thatthe change in potential is proportional to the change in ion activity (in logarithmic units) of the system. ISE measurement involves the use of two electrodes, one is the working (indicator) electrode, and the other electrode is the reference electrode whose potential is fixed irrespective of the solution used. The potential that is proportional to the activity of the sample ion is measured across these two electrodes. Typical calibration curve of a potentiometric sensor determined in this way is shown in figure 2. Copyright 2016.All rights reserved. 178PDF Image | ION SELECTIVE ELECTRODES OVERVIEW
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