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potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
potentiometry & ion selective electode
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potentiometry & ion selective electode

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  • 1. POTENTIOMETRY & ION SELECTIVE ELECTRODE DR.RUCHI GOKANI Dept of biochemistry s.b.k.s.m.i.r.c
  • 2. Potentiometry  In potentiometry, the potential of an electrochemical cell is measured under static conditions because no current flows while measuring a solution’s potential.  Use of electrodes to measure voltage that provide chemical information.  Concentration of ions in solution is calculated from the measured potential difference between the two electrodes immersed in solution under condition of zero current.  This type of system includes at least two electrodes, identified as an indicator electrode (right half-cell) and a reference electrode (left half-cell ) which act as the cathode and anode respectively.
  • 3.  Each electrode is in contact with either the sample (in the case of the “indicator electrode”) or a reference solution ( in the case of the “reference electrode”).  Electrodes + solution = electrochemical cell Each electrode represent half cell reaction with correspondance half cell potential.
  • 4. Potentiometer • A device for measuring the potential of an electrochemical cell without drawing a current or altering the cell’s composition. • The potential is measured under static conditions. • Because no current, or only a negligible current flows while measuring a solution’s potential, its composition remains unchanged. • For this reason, potentiometry is a useful quantitative method.
  • 5. • Two electrodes connected to Potentiometer to measure potential difference • Indicator electrode (Eind) – potential respond to change according to conc. of ions • Reference electrode (Eref) – half cell potential does not change. Ecell = Eind ─ Eref + Elj
  • 6. Schematic diagram of an electrochemical cell of potentiometric measurement Example 1
  • 7.  System Components  Liquid Junction  Reference electrode  Indicator or measuring electrode  Readout device (Potentiometer)
  • 8.  Liquid junction – also known as a salt bridge are required to complete the circuit between the electrodes. Functions: It allows electrical contact between the two solutions. It prevents the mixing of the electrode solutions. It maintains the electrical neutrality in each half cell as ions flow into and out of the salt bridge.
  • 9.  Reference Electrode- is an electrochemical half-cell that is used as a fixed reference for the measurement of cell potentials.  A half-cell with an accurately known electrode potential, Eref, that is independent of the concentration of the analyte or any other ions in the solution  Always treated as the left-hand electrode Examples: Normal hydrogen electrode Saturated calomel electrode Ag-AgCl electrode
  • 10. Reference Electrodes Calomel electrode- composed of mercury/mercurous chloride; It is dependable but large, bulky, and affected by temperature. Silver/silver chloride- Widely used because simple, inexpensive, very stable and non-toxic. o reference electrodes are more compact -- overall better & faster Normal Hydrogen Electrode- consists of a platinized platinum electrode in HCl solution with hydrogen at atmospheric pressure bubbled over the platinum surface. -determination of pH of the solution.
  • 11. Saturated calomel electrode
  • 12. Silver-silver chloride electrode Standard hydrogen electrode (SHE)
  • 13. Indicator or measuring electrode • The potential of this electrode is proportional to the concentration of analyte. • Two classes of indicator electrodes are used in potentiometry: o metallic electrodes • Electrodes of the first kind • Electrode of the second kind • Redox electrode o membrane electrodes (ion-selective electrodes) • glass pH electrode
  • 14. Metallic electrodes Electrodes of the first kind • A metal in contact with a solution containing its cation. • The potential is a function of concentration of Mn+ in a Mn+ / M. The most common ones: o Silver electrode (dipping in a solution of AgNO3) • Ag+ + e ↔ Ag o Copper electrode • Cu+2 + 2e ↔ Cu o Zn electrode • Zn+2 + 2e ↔ Zn
  • 15. Electrode of the second kind • A metal wire that coated with one of its salts precipitate. • Respond to changes in ion activity through formation of complex. • A common example is silver electrode and AgCl as its salt precipitate. • This kind of electrode can be used to measure the activity of chloride ion in a solution.
  • 16. Redox electrode • An inert metal is in contact with a solution containing the soluble oxidized and reduced forms of the redox half-reaction. • The inert metal is usually is platinum (Pt). • The potential of such an inert electrode is determined by the ratio of the reduced and oxidized species in the half-reaction. • A very important example of this type is the hydrogen electrode.
  • 17.  Indicator Electrode- also called the measuring electrode It is immersed in a solution of the analyte, develops a potential, Eind that depends on the activity of the analyte. Is selective in its response It is the other electrochemical half-cell that responds to changes in the activity of a particular analyte species in a solution. Example: Ion-Selective Electrodes
  • 18. Ion selective electrode  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.  indicator electrode based on determination of cations or anions by the selective absorption of these ions to a membrane surface.
  • 19. TYPES OF ION SELECTIVE ELECTRODE •Glass Membrane Electrode •Solid State Electrode •Liquid Membrane Electrode •Gas Sensing Electrode
  • 20. GLASS MEMBRANE ELECTRODE • Responsive to univalent cations ( H+ , Na+) • Glass electrodes available for Na+, K+, NH4+, Li+, Ag+(cations only) by varying glass composition • The selectivity for this cation by varying the composition of a thin ion sensitive glass membrane. • Glass membrane manufactured from SiO2 with negatively charged oxygen atom. • Inside the glass bulb, a dilute HCl solution and silver wire coated with a layer of silver chloride. • The electrode is immersed in the solution and pH is measured • Example: pH electrode
  • 21. Glass pH electrode • Advantages over other electrodes for pH measurements: o Its potential is essentially not affected by the presence of oxidizing or reducing agents. o It operates over a wide pH range. o It responds fast and functions well in physiological systems. o Selective for monovalent cations only because polyvalent ions can not penetrate the surface of membrane.
  • 22. pH electrode  Selective for the detection of hydrogen ions.  The measuring or indicator electrode has a “glass membrane”  pH is then determined from potential between the pH electrode and a standard reference electrode.
  • 23. SOLID STATE ELECTRODE • Solid state electrode are selective primarily to anions. • It may be a - homogenous membrane electrode - heterogeneous membrane electrode. • Homogenous membrane electrode: ion-selective electrodes in which the membrane is a crystalline material (AgI/Ag2S).
  • 24. • Heterogeneous membrane electrode: ion-selective electrodes prepared of an active substance, or mixture of active substances (silicone rubber or PVC) • Example: Fluoride ion selective electrode
  • 25. LIQUID MEMBRANE ELECTRODE • Liquid membrane is a type of ISE based on water- immiscible liquid substances produced in a polymeric membrane used for direct potentiometric measurement. • Used for direct measurement of several polyvalent cations (Ca ion) as well as a certain anions. • Inner compartment of electrode contains reference electrode & aqueous reference solution. • Outer compartment – organic liquid ion exchanger
  • 26. •The polymeric membrane made of PVC to separate the test solution from its inner compartment which contains standard solution of the target ion. •The filling solution contains a chloride salt for establishing the potential of the internal Ag/AgCl wire electrode.
  • 27. GAS SENSING ELECTRODE • Available for the measurement of ammonia, carbon dioxide and nitrogen oxide. • This type of electrode consist of permeable membrane and an internal buffer solution. • The pH of the buffer changes as the gas react with it. • The change is detected by a combination pH sensor. • This type of electrode does not require an external reference electrode.
  • 28.  Measurement of PCO2 in routine blood gases  A modified pH electrode with a CO2 permeable membrane covering the glass membrane surface  A bicarbonate buffer separates the membranes  Change in pH is proportional to the concentration of dissolved CO2 in the blood pco2 electrode
  • 29. Application of Potentiometric Measurement • Clinical Chemistry o Ion-selective electrodes are important sensors for clinical samples because of their selectivity for analytes. o The most common analytes are electrolytes, such as Na+, K+, Ca2+,H+, and Cl-, and dissolved gases such as CO2. • Environmental Chemistry o For the analysis of of CN-, F-, NH3, and NO3 - in water and wastewater.
  • 30. • Potentiometric Titrations o pH electrode used to monitor the change in pH during the titration. o For determining the equivalence point of an acid–base titration. o Possible for acid–base, redox, and precipitation titrations, as well as for titrations in aqueous and nonaqueous solvents. • Agriculture o NO3, NH4, Cl, K, Ca, I, CN in soils, plant material, fertilizers. • Detergent Manufacture o Ca, Ba, F for studying effects on water quality
  • 31. • Food Processing o NO3, NO2 in meat preservatives o Salt content of meat, fish, dairy products, fruit juices, brewing solutions. o F in drinking water and other drinks. o Ca in dairy products and beer. o K in fruit juices and wine making. o Corrosive effect of NO3 in canned foods.
  • 32. advantages • Relatively inexpensive and simple to use and have an extremely wide range of applications and wide concentration range. • Under the most favourable conditions, when measuring ions in relatively dilute aqueous solutions and where interfering ions are not a problem, they can be used very rapidly and easily. • ISEs can measure both positive and negative ions. • They are unaffected by sample colour or turbidity.
  • 33. • Non-destructive: no consumption of analyte. • Non-contaminating. • Short response time: in sec. or min. useful in industrial applications.
  • 34. LIMITATION • Precision is rarely better than 1%. • Electrodes can be affected by proteins or other organic solutes. • Interference by other ions. • Electrodes are fragile and have limited shelf life.

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