Potentiometry.pptx

Potentiometry passively measures the potential of a solution between two electrodes, affecting the solution very little in the process. One electrode is called the reference electrode and has a constant potential, while the other one is an indicator electrode whose potential changes with the composition of the sample. Therefore, the difference of potential between the two electrodes gives an assessment of the composition of the sample. Potentiometry usually uses indicator electrodes made selectively sensitive to the ion of interest, such as fluoride in fluoride selective electrodes, so that the potential solely depends on the activity of this ion of interest.

1. Potentiometry Mansi Narendrasinh Chauhan M.Pharm.

2. Modern Pharmaceutical Analytical Techniques Topic: Potentiometry Guided by Dr. Shailesh Luhar & Mrs. Neha Vadgama Presented By MANSI NARENDRASINH CHAUHAN M.Pharm Pharmaceutical Quality Assurance Smt. BNB Swaminarayan Pharmacy College Salvav-Vapi

3. CONTENTS Introduction Theory Principle Instrumentation Construction Electrodes Ion selective electrodes Application Potentiometric titration 1/5/2022 MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 3

4. INTRODUCTION Potentiometry is an electrochemical method of Analysis deals with the measurement of electric potential or emf of an electrolyte solution under the condition of constant current. Potentiometry is the measurement of electrical potential of an electrolyte solution to determine its concentration. The principle is based on the fact that the potential of the given sample is directly proportional to the concentration of its electro active ions or its activity (pH). When the pair of electrodes is placed in the sample solution it shows the potential difference by the addition of the titrant or by the change in the concentration of the ions. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 4

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6. THEORY In potentiometric measurements, the potential between two electrodes is measured using a high impedance voltmeter. It is usually employed to find the concentration of a solute in solution. The theory of potentiometry is based on the Nernst equation. It gives the basic relationship between the potential generated by an electrochemical cell and the concentration of the ions. The potential E ( Half cell potential) of any electrode is given by Nernst equation. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 6

7. NERNST EQUATION MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 7

8. ELECTROCHEMICAL CELL It is a device which converts Chemical energy into electrical energy. It is used to generate potential and electric current from chemical reactions. It consists of two electrodes immersed in an electrolyte solution. The current is generated by the chemical reactions which involves releasing and accepting of electrons at the two electrodes (Redox reactions). Each electrode of an electrochemical cell is referred to as Half cell, one half cell loses electrons(oxidation) other half cell gains electrons(reduction). One half cell is called as reference electrode, which has stable and constant potential and the other is called as indicator electrode the potential of which is to be determined. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 8

9. PRINCIPLE The principle involved in the Potentiometry is when the pair of electrodes is placed in the sample solution it shows the potential difference by the addition of the titrant or by the change in the concentration of the ions. Potentiometric methods of analysis are based upon measurements of the potential of electrochemical cells under conditions of zero current, where the Nernst equation governs the operation of potentiometry MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 9

10. INSTRUMENTATION Instrumentation typically used in potentiometry includes the Reference electrode , with a known potential, constant over time and independent of the composition of the solution containing the analyte in which it is immersed, and An Indicator (or working) electrode, whose response depends on the concentration of the analyte, and Finally an instrument for measuring potential ‘voltmeter’. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 10

11. CONSTRUCTION OF POTENTIOMETER At its most fundamental level, a potentiometer consists of two electrodes inserted in two solutions connected by a salt bridge The voltmeter is attached to the electrodes to measure the potential difference between them. One of the electrodes is a reference electrode, whose electrode potential is known and remains constant when dipped into respective solution. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 11

12. CONSTRUCTION OF POTENTIOMETER The other electrode is the indicator electrode. The indicator electrode is immersed in a solution, whose concentration you want to determine. Indicator electrode potential is dependent on activity of ions into solution, activity is nothing but concentration of active ions of solute in solution thus this potential directly indicates the concentration of solution. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 12

13. WHAT EXACTLY IS ELECTRODE POTENTIAL? To carry out the process of electrolysis, we need electricity to break the constituent particles in the electrolyte. This application of electricity creates potential difference across the electrolytic cell depending upon the nature and construction of electrode. again (the ability to carry out electrolysis) This potential difference is created as a result of the difference between individual potentials of the two metal electrodes with respect to the electrolytes. After application of electricity the tendency of an electrode to lose or gain electrons when placed in solution is known as electrode potential. Here in Potentiometry instrument we have two electrodes : Reference Electrode and Indicator Electrode. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 13

14. ELECTRODES Electrodes: These are mainly used to measure the voltages. Types of electrodes 1.Reference Electrode a. Primary Reference electrode : Standard hydrogen electrode(SHE) b. Secondary Reference electrode 1.Saturated calomel electrode(SCE) 2.Mercury mercurous sulphate electrode 3.Silver silver chloride electrode 4.Mercury mercuric oxide electrode MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 14

15. ELECTRODES 2. Indicator Electrodes Hydrogen Electrode Quinhydrone electrode Antimony Antimony Oxide electrode Glass electrode 3. Combination pH Electrode 4. Oxidation reduction electrode MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 15

16. ELECTRODES 5. Ion Selective Electrodes Glass membrane electrode Liquid membrane electrode Solid state electrode/sensor Biocatalytic Membrane electrode MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 16

17. STANDARD HYDROGEN ELECTRODE Construction: Hydrogen electrode consists of two main components: enclosing tube and conductor. Enclosing tube – It is made from glass material and it consist of conductor wire (platinum). Through this hydrogen gas passed under 1 atmospheric pressure which reacts at conductor surface. Conductor – It is made from platinum foil which is coated with platinum black (means it is platinized) and attached to platinum wire which is connected with high impedance voltmeter. Because of finely divided platinum present at electrode surface rapid reaction occurs. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 17

18. STANDARD HYDROGEN ELECTRODE Working: When the circuit is formed hydrogen is either oxidized to Hydrogen ion (if electrode is anode) or it is reduced to hydrogen gas (if electrode is cathode). Potential of SHE: Potential value depends upon three factors such as follow: Temperature of Pt/H2 Hydrogen ion activity in solution Pressure of Hydrogen at electrode surface (Here, Hydrogen gas must be at 1 atm pressure) MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 18

19. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 19 STANDARD HYDROGEN ELECTRODE

20. CALOMEL ELECTRODE It consists of mercury in contact with solution that is saturated with mercurous chloride (Hg2Cl2) and known concentration of KCl. Depending on the concentration of KCl these calomel electrodes are divided into three types: Decimolar Calomel Electrode (KCl conc: 0.1M) Molar Calomel Electrode (KCl conc: 1M) Saturated Calomel Electrode (KCl conc: Saturated, above 4.5M ) MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 20

21. CALOMEL ELECTRODE Construction: It consist of Inner tube and Outer tube. Inner tube - Inner tube filled with Hg(l) and Hg2Cl2, KCl. Small hole present at bottom of inner tube which connects it to outer tube. Outer tube - outer tube are made from glass material and it possesses Porous wick at bottom which connects it with analyte solution and acts as small bridge. saturated calomel electrode (SCE) the concentration of Cl– is determined by the solubility of KCl. The electrode consists of an inner tube packed with a paste of Hg, Hg2Cl2, and KCl, situated within a second tube containing a saturated solution of KCl. A small hole connects the two tubes and a porous wick serves as a salt bridge to the solution in which the SCE is immersed. A stopper in the outer tube provides an opening for adding addition saturated KCl. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 21

22. CALOMEL ELECTRODE MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 22 Working: The potential of a calomel electrode, therefore, is determined by the activity of Cl– in equilibrium with Hg and Hg 2 Cl 2 . Because the concentration of Cl– is fixed by the solubility of KCl, the potential of an SCE remains constant even if we lose some of the solution to evaporation. A significant disadvantage of the SCE is that the solubility of KCl is sensitive to a change in temperature. At higher temperatures the solubility of KCl increases and the electrodes potential decreases.

23. SILVER-SILVER CHLORIDE ELECTRODE Construction: It consists of glass tube, in which silver coated wire is dipped into the solution of KCl of known concentration which is saturated with Silver chloride. Schematic diagram shows Ag / AgCl electrode. Because the electrode does not contain solid KCl, this is an example of an unsaturated Ag / AgCl electrode. Porous plug is present at bottom of tube allowing electrical contact of electrode. Working: based on the redox couple between AgCl and Ag. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 23

24. ION-SELECTIVE ELECTRODES An ion-selective electrode (ISE), also known as a specific ion electrode (SIE), is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or pH meter. An ideal I.S.E. consists of a thin membrane across which only the intended ion can be transported. The transport of ions from a high conc. to a low one through a selective binding with some sites within the membrane creates a potential difference. Ion Selective Electrodes (including the most common pH electrode) work on the basic principal of the galvanic cell .By measuring the electric potential generated across a membrane by "selected" ions, and comparing it to a reference electrode, a net charge is determined. The strength of this charge is directly proportional to the concentration of the selected ion. The basic formula is given for the galvanic cell: • Ecell= E ISE - Eref MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 24

25. CLASSIFICATION OF MEMBRANES A. Crystalline Membrane Electrodes Single crystal Example: LaF3 for F Polycrystalline or mixed crystal Example: Ag2S for S2- and Ag + B. Nanocrystalline Membrane Electrodes Glass Examples: silicate glasses for Na+ and H+ Liquid Examples: liquid ion exchangers for Ca2+ and neutral carriers for K+ Immobilized liquid in a rigid polymer Examples: PVC matrix for Ca2+ and NO3- MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 25

26. PROPERTIES OF ION SELECTIVE MEMBRANES Minimal solubility: A necessary property of an ion-selective medium is that its solubility in analyte solutions approaches zero. Thus. many membranes are formed from large molecules Of molecular aggregates such as silica glasses Of polymeric resins. Ionic inorganic compounds of low solubility, such as the silver halides, can also be converted into membranes. Electrical conductivity: A membrane must exhibit some electrical conductivity, albeit small. Generally, this conduction takes the form of migration of singly charged ions within the membrane. Selective reactivity with the analyte: A membrane or some species contained within the membrane matrix must be capable of selectively binding the analyte ion. Three types of binding are encountered: ion-exchange, crystallization. and complexation. The former two are the more common, and we will largely focus on these types of bindings. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 26

27. GLASS MEMBRANE ELECTRODE The glass contain 60 to 75 mole % SiO2, 2 to 20 % Al2O3or LaF3, 0 to 6 % BaO and CaO, and a variable amount of a group 1A oxide. Inside the glass bulb contains a dilute HCl solution and silver wire coated with a layer of silver chloride. By altering the composition of the glass, it is possible to make the electrode selective for different ions. Glass membranes are selective for monovalent cations because polyvalent ions cannot easily penetrate the surface of the membrane. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 27

28. GLASS MEMBRANE ELECTRODE The selectivity of glass electrodes is related both to the ability of the various Monovalent cations to penetrate into the glass membrane and to the degree of attraction of the cations to the negative sites within the glass. Glass electrodes which are selective for H+(pH electrode),Li+, Na+, K+, Cs+, Ag+, Ti+ and NH4+ are commercially available. Monovalent cations from a solution into which the glass is dipped can penetrate into the surface of the glass. The concentration of the analyzed ion in the sample solution changes from that in the internal reference solution, a potential difference develops across the membrane. The electrode is immersed in the solution and pH is measured. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 28

29. SOLID STATE MEMBRANE ELECTRODE A solid state membrane electrode can be a single crystal, a pellet made from a sparingly soluble salt, or a sparingly soluble salt embedded in an inert matrix, e.g., rubber. The single crystal and pellet membranes are homogenous, electrodes containing them are referred to as homogenous membrane electrodes. The membrane consisting of the sparingly soluble salt in the inert binding material is a heterogeneous membrane electrode. • The lanthanum fluoride (LaF3) membrane is the only single crystal membrane that is widely used in ion selective electrodes. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 29

30. SOLID STATE MEMBRANE ELECTRODE In the process of “doping”, the resistance of the LaF3 crystal is decreased by replacing a relatively small number of La3+ ions in the crystals with Eu2+ ions (Ionic charge transport). Because fluoride can selectively migrate to the crystal, the lanthanum fluoride membrane is selective for fluoride. Vacancies in the crystalline structure have exactly the proper size, charge, and shape to hold a fluoride ion. Fluoride ions migrate from vacancy to vacancy in the defective LaF3 crystal. As a fluoride ion abandons one position in the crystalline structure, it leaves a hole into which another fluoride can migrate. The result is a crystal which exhibits ionic conductivity. The conductance to the membrane, as well as the potential across the membrane, can be related to the analyte concentration for many solid state membrane electrodes. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 30

31. SOLID OR LIQUID MATRIX ELECTRODES The membrane of the electrode uses an ion exchanger permanently embedded in a plastic material that is sealed to the electrode body. The membrane separates the internal filling solution and reference from the external sample solution. The electrode resembles that of solid state electrode. The sites are free to move in the active phase(the membrane) this makes the electrodes selective for multivalent ions over univalent ions. These liquid membrane electrodes are responsive exactly to those ions ( Ca2+ , ClO4 -, NO3 - and BF4-) That are extremely difficult to monitor by other techniques. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 31

32. GAS SENSING ELECTRODE A gas permeable membrane is used to isolate the analytes from possible interferences in the sample. A thin buffer layer is used to trap the analyte gas and covert it to some ionic species that can be detected potentiometrically. Gas sensing electrodes are available for the measurement of carbon dioxide, nitrite and Sulphur dioxide. These are simple and reliable but they tend to have a relatively slow response and recovery time(often 30 seconds to 5 minutes). MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 32

33. GAS SENSING ELECTRODE They are used to assay the gases dissolved in aqueous solutions. It is constructed by enclosing the glass pH membrane in a second, gas permeable hydrophobic membrane. A thin layer of an electrolyte solution is held between the two membranes. They also have a small reference electrode enclosed within the gas permeable membrane . MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 33

34. GAS SENSING ELECTRODE The potential between the internal ISE and the reference electrode within the outer membrane is monitored. The gas permeable membrane holds a constant volume of solution around the internal ISE into which the gaseous analyte can diffuse. The hydrophobic gas-permeable membrane can be composed of substance which allows passage of dissolved gas but prevents the solution within the membrane from escaping. The materials used are silicon rubber, Teflon polypropylene, fluorinated ethylene propylene, polyvinylidene fluoride etc. Gas from the sample solution passes through the submerged gas permeable membrane and equilibrates in the electrolyte solution between the two membranes. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 34

35. GAS SENSING ELECTRODE The gas reacts reversibly with the electrolyte solution to form an ion to which the ion selective electrode responds. Because the activity of the ion that is formed between the two membranes is proportional to amount of gas dissolved in sample, the electrode response is directly related to the activity of the gas in the sample. The gases (primarily NH3, SO2 and CO2) which are detected by gas sensing electrodes based on the pH electrode equilibrate with the electrolyte solution to alter its pH: NH3+ H2O = NH4+ + OH- SO2+ H2O = HSO3- + H+ CO2+ H2O = HCO3- + H+ MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 35

36. AIR GAP ELECTRODES They are another form of gas sensing electrodes invented by Ruziicka and Hansen. A very thin layer of an appropriate electrolyte solution is adsorbed on the surface of the membrane of the glass electrode. The electrolyte solution is adsorbed on glass membrane when membrane comes in contact with the sponge containing the electrolyte solution and a wetting agent. The reference electrode makes contact with the adsorbed electrolyte layer through a small, porous, ceramic salt bridge. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 36

37. AIR GAP ELECTRODES The air gap electrode is used to assay ionic species which can be chemically converted to gases, e.g. HCO3- The HCO3-solution is placed in the sample holder and an acid is added to convert HCO3- (aq) to CO2(g). The sample holder is placed in position under the electrode and stirred with a magnetic stirrer and stirrer bar. Carbon dioxide which is emitted during the chemical reaction equilibrates with the electrolyte solution on the glass membrane and alters the pH of the solution. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 37

38. AIR GAP ELECTRODES The glass electrode measures the pH of the resulting solution. The electrolyte solutions used with air gap electrode are the same as those used with other gas-sensing electrodes. The air-gap electrode has a faster response time due to the thinner layer of electrolyte solution and a longer lifetime than most of the other types of sensing electrodes. A typical response time for an air-gap electrode is less than a minute. Air-gap electrode is primarily used for analysis of NH4+, HSO3- As an example they can be used for the determination of urea in blood. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 38

39. NEUTRAL CARRIER MEMBRANE ELECTRODE They have the same design as liquid-ion-exchanger membrane electrodes. The liquid-ion-exchanger is replaced in neutral-carrier membranes with a neutral complexing agent (a neutral carrier) such as crown ether, which is dissolved in a highly water insoluble organic solvent. The neutral carrier complexes with the analyte at membrane- sample interface to form a charged complex which is extracted from the aqueous solution into the organic solvent in the membrane. The selectivity of the membrane for a particular ion depends upon the ability to extract the ion into the membrane, which in turn depends upon the ability of the ion to form a complex with the neutral carrier. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 39

40. NEUTRAL CARRIER MEMBRANE ELECTRODE After complexation and extraction, the species in the neutral-carrier membrane has the same charge as the extracted ion. The solvent in which the neutral carrier is dissolved is usually a high boiling organic compound such as nitrobenzene (used in Ba2+ selective electrodes), dibutylsebacate (used in K+ selective electrode) and o-nitrophenyl-n-octyl ether (used in a Ca2+ selective electrode). The physical support for the neutral carrier and solvent is usually a cellulose membrane, more commonly, a PVC membrane. In addition to K+, Ca2+, Ba2+, neutral-carrier membrane electrodes are also selective for Li+, H+, Mg2+, NH4+, Sr2+. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 40

41. COATED WIRE ELECTRODE They are considerably smaller than other forms of ion selective electrodes because the internal filling solution is eliminated and the ion selective membrane is coated directly on the internal electrode wire. The ion selective membranes utilized in coated wire electrodes consists of either an ion exchanger or neutral carrier immobilized in a polymeric material that is coated on the electrode. They are more sturdy than other ISEs and can be constructed with small tips. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 41

42. COATED WIRE ELECTRODE First the metal on the interior of the electrode is sealed into a glass or some other suitable material so that several mm or less of the wire is exposed. The exposed wire is successively dipped into a solution of the polymeric material and then into a solution of the ion exchanger or neutral carrier. After the electrode has air-dried, the dipping procedure is repeated, if necessary, until the membrane coating on the wire is the desired thickness. Alternatively, the wire can be dipped into a single solution containing both the membrane material and the polymerizer. The polymeric matrix can be any of materials including PVC, polymethyl acrylate(PMM) or epoxy. The internal electrode can be constructed from metals like platinum, copper, silver wire and graphite rods. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 42

43. ION SELECTIVE FIELD EFFECT TRANSISTORS The electrode consists of an ion selective membrane deposited or coated on the gate of a field effect transistor (FET). The membrane can be a sparingly soluble compound such as silver bromide (solid state membrane) or some other type of membrane such as an ion exchanger or neutral carrier in a PVC matrix. Often membranes in a PVC matrix are used. Membranes in a PVC matrix can be forced to adhere to the gate of the FET by placing a polyimide mesh over the gate prior to coating it with the membrane. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 43

44. ION SELECTIVE FIELD EFFECT TRANSISTORS The potential at the membrane is partially determined by the activity of the analyte in solution. That potential determines the flow of current through the drain of the FET. The drain current consequently varies with the activity of the analyte and is the monitored factor. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 44

45. BIO MEMBRANE ELECTRODES It is an ion selective electrode which is coated with an enzyme- containing acrylamide gel. The gel and enzyme are held in place on the surface of the ion selective electrode by an inert physical support. The design is same as gas-sensing electrode. The support is a sheet of cellophane or a piece of gauze made from Dacron or nylon. The physical support is wrapped around the electrode membrane and tied in place. The acrylamide gel containing the enzyme is coagulated on the support-electrode combination. Enzymes are highly selective biochemical catalysts. The selectivity of Bio membrane electrode is due to the selectivity of the enzymes that are used in electrodes. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 45

46. BIO MEMBRANE ELECTRODES Here the enzyme-catalyzed reaction of the analyte yields an ionic reaction product which is monitored by the internal ion-selective electrode. The operation of the urea-selective electrode will serve to illustrate the operation of Bio membrane electrodes. The glass membrane of an ammonium-sensitive glass electrode is coated with an acrylamide gel layer containing the enzyme urease. When the electrode is dipped into a solution containing urea, the following reaction occurs to yield NH4+ : CO(NH2)2+ H2O 2NH4+ + CO2- . The NH4+ formed during the reaction is measured at the ammonium- selective electrode. A working curve is prepared by plotting the potential of the electrode in standard urea solutions as a function of the logarithm of urea concentration. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 46

47. BIO MEMBRANE ELECTRODES The urea concentration in the sample is obtained from the working curve. Unfortunately the enzymes used in Bio membrane electrodes gradually decay and the enzyme containing gel must be periodically replaced. The Bio membrane of urea electrode lasts about 2 weeks. Bio membrane electrodes have long response time of 5 or more minutes. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 47

48. APPLICATION OF POTENTIOMETRY Ion-selective electrodes are used in a wide variety of applications for determining the concentrations of various ions in aqueous solutions. The electrodes can be used as an end point detector in a titration. Pollution Monitoring: CN, F, S, Cl, NO3 etc., in effluents, and natural waters. Agriculture: NO3, Cl, NH4, K, Ca, I, CN in soils, plant material, fertilizers and feedstuffs. Food Processing: NO3, NO2 in meat preservatives. Salt content of meat, fish, dairy products, fruit juices, brewing solutions. F in drinking water and other drinks. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 48

49. APPLICATION OF POTENTIOMETRY Detergent Manufacture: Ca, Ba, F for studying effects on water quality. Determination of equilibrium constants. Determination of ionic product of water. Determination of Dissociation constant of acids. Biochemistry: Analysis of Ca, K, Cl in body fluids like blood, plasma, sweat and serum. Paper Manufacture: S and Cl in pulping and recovery cycle liquors. F in skeletal and dental studies. Ca in dairy products and beer . Explosives: F, Cl, NO3 in explosive materials and combustion products. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 49

50. POTENTIOMETRIC TITRATION Acid-base titration: An acid-base titration is a quantitative analysis used to determine the acid or base concentration by precisely neutralizing the acid or base with a known concentration standard solution. Titration of HCl with NaOH is an example in which a pH indicator (Generally phenolphthalein) is used to produce color by which the equivalence point or endpoint of the reaction determines. It is also can be performed by potentiometric titration however it doesn’t need an indicator.  Redox titration: It is a type of titration it includes the use of a redox indicator or potentiometer. It works based on an oxidation-reduction reaction between the titrant and the compound. Iodometry, permanganometry, bromatometry, cerimetry, and dichrometry are some of the most used redox titrations. A platinum or calomel electrode is also used in redox titration using a potentiometer. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 50

51. POTENTIOMETRIC TITRATION Complexometric titration: In this type of potentiometric titration, membrane electrodes are used to determine the concentration of metal ions in the compound sample. In the reaction of this method, a metal indicator complex is formed when the metal ion reacts with the indicator. Complexometric titration consists of replacement titration, back titration, direct titration, and indirect titration. Precipitation titration: It is a titration method that involves the formation of precipitates throughout the process of titration. The titrant reacts with the solute to form an insoluble substance, and the titration is carried until the last drop of the solute has been consumed. Depending on the type of application it consists of Volhard’s method, Mohr's method, and Fagan’s method. MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 51

52. REFERENCES Douglas A. Skoog, F james holler, stanley R. Crouch, (2007) sixth edition, principles of instrumental analysis, thomson brooks/ cole . G.H. Jeffery, j. Bassett, j. Mendham, r. C. DENNEY, (1989) fifth edition, vogel's textbook of quantitative chemical analysis, longman group UK limited. Frank a settle, (1993) handbook of instrumental techniques for analytical chemistry. Http://destinationpharmagens.Com/wpcontent/uploads/2019/10/POTENTIOMETRY.Pdf Britannica, the editors of encyclopaedia . “Potentiometry". Encyclopedia britannica , 23 nov. 2021, https://www.Britannica.Com/science/potentiometry. Accessed 2 january 2022 . MANSICHAUHAN Smt. B.N.B. SPC, Salvav-vapi 1/5/2022 52