Investigation of Some Electronic Properties of Combined pH Electrode Shantaram L. Bonde 1 , 1 Department of Chemistry Nowrosjee Wadia College Pune,India-411001 Suchita P. Bhangale 2 and Pravin K. Bhadane 2 2 Department of Electronics Nowrosjee Wadia College Pune,India-411001. Abstract— Some electronic properties of combined pH electrode have been investigated with the help of electronic circuits. Electrode-electrolyte resistance has been measured by half deflection method and its value depends on the thickness of glass. The bulk resistance of test solution, internal solution of glass and reference electrodes have been measured by AC Wheatstone’s bridge and they are dependent on ionic concentration. The capacitance of glass electrode has been measured by de Sauty’s bridge. The impedance of double screened co-axial cable has measured by LCR meter. The measured values of resistance and capacitance are matching with the desired values. Present study is useful to the electronic engineers for designing of preamplifier section of pH meter. Keywords—combined pH electrode, electrode-electrolyte resistance, AC Wheatstone’s bridge, de Sauty’s bridge. I. INTRODUCTION pH measurement is generally done with the use of a combination electrode. The combination electrode is an electrode system formed by a glass half-cell which works as measuring electrode and reference half- cell. A potential develops on the membrane surface when a pH electrode comes in contact with a sample and its value varies with the pH of the sample [1]. The voltage signal produced by the pH electrode is a very small, high impedance signal. Due to this reason, the voltmeter is not directly connected to the pH electrode. An interface of amplifier with high input impedance is required between the electrode and voltmeter. With the age of glass electrode, its resistance changes. Generally it increases due to chemical deposition and deformation due to thermal effect. This resistance change alters the electrode potential. For this cause, electrode should be calibrated regularly. The resistance of electrode depends on the type of material used for making the glass balloon. The balloon of pH electrode is made from a special glass composed of alkali metal ions [2-4]. The alkali metal ions of the glass and the hydrogen ions in solution undergo an ion exchange reaction generating a potential difference. Electronically, the ion exchange is equivalent to the leakage of charge through the glass membrane. The glass membrane forms the solid dielectric medium of non-polar capacitor. The internal ionic buffer solution and the external test solution form the plates of capacitor. The value of capacitance depends on the thickness of glass membrane and the ionic concentration of solutions. The response time of pH measurement depends on the capacitance. The potential of the reference portion is produced by the internal element in contact with the reference fill solution. The potential at glass electrode is measured with reference to the potential of reference electrode. In order to measure the correct potential due to test solution, the potential of reference electrode should be constant [5]. For this reason, the fill solution should contain constant number of ions. The saturated solution of salt, such as KCl, has more ions and less resistance of the order of 2000 Ω. The present work deals with the measurement of resistance and capacitance of combined pH electrode. The resistance of glass and solution were measured by half deflection method and AC Wheatstone’s bridge respectively. The capacitance of glass was measured by the de Sauty’s bridge method. The rest of article is organized as follows: in section II electrical equivalent circuit of combined pH electrode is discussed. The design of electronic circuits, their description and results are discussed in section III. Finally, the conclusion and the future scope of present work are discussed in section IV. II. METHOD In the present work, electronic parameters of combined electrode have been measured by designing the electronic circuits. Figure 1 shows the combined electrode and it also shows the corresponding equivalent electronic components. The balloon of glass electrode forms the electrode-electrolyte interface and it is equivalent to the parallel combination of resistor (R g ) of glass and capacitor (C g ) with glass as dielectric. The internal and external ionic solutions form the plates of parallel plate capacitor. The resistance of internal solution (R int ) is in series with R g and Ag/AgCl wire. The R g and C g are given by [6], R g = ρ ×d B , C g = ε 0 ×k×A d Where, ρ=specific resistance, d= thickness, B= cross- sectional area, ɛ 0 = permittivity of free space, k=dielectric constant, A=surface area of balloon. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 www.ijert.org IJERTV3IS090891 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Vol. 3 Issue 9, September- 2014 1114