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Ion selective electrodes

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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
  • The voltage is theoretically dependent on the logarithm of the ionic activity, according to the Nernst equation in a solution into an electrical potential

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Approximately 20 types of ion selective electrodes are currently present

Applications:

  • Pollution control
  • Biomedical research
  • Clinical medicine
  • Food processing
  • Metallurgy

Direct measurement of sodium, potassium, calcium, nitrate, chloride and sulfide

Some electrodes measure dissolved gases like ammonia, sulphur-dioxide and carbon-dioxide

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Principle of ISE

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Ion Selective membranes currently available are

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CATIONS:

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Ammonium (NH4+), Barium, Calcium, Cadmium,

copper, lead, Mercury, Potssium, Sodium,Silver

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ANIONS:

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Bromide,Carbonate,Chloride, Cyanide, Fluoride, Iodide, Nitrate, Perchlorate, Sulphide, Thiocynate

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Types of ISE

  • Glass membrane electrode
  • Liquid membrane electrode
  • Solid State membrane electrode

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Glass Membrane Electrode

  • A glass electrode is a type of ion-selective electrode made of a doped glass membrane that is sensitive to a specific ion.

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  • Glass Containing less than 1% of Al2O3 gives good response for pH measurement

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  • Glasses having 11% Na2O, 18% Al2O3, and 71% of SiO2 are highly sensitive to sodium and other alkali metal ions used for clinical work

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Liquid Membrane Electrodes

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Liquid Membrane Electrodes

  • Another class of ion-selective electrodes uses a hydrophobic membrane containing a liquid organic complexing agent that reacts selectively with the analyte
  • Three types of organic complexing agents have been used: cation exchangers, anion exchangers, and neutral ionophores

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  • Porous liquid membrane is replaced with polyvinyl chloride membrane
  • Liquid ion exchanger and polyvinyl chloride are dissolved in solvent (tetrahydrofuran)
  • Evaporating this solvent leaves a flexible membrane
  • Eg: Potassium electrode based on valinomycin
  • Calcium liquid membrane electrode membrane another example

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Solid State Membrane Electrodes

  • Pellet of crystalline material doped with rare earth material
  • Arrangement-internal ref electrode (Pt or Ag-AgCl)in reference solution with 0.1 M each in NaF and NaCl
  • Body of the electrode is made of teflon
  • Membrane held in position with epoxy resin
  • Example: Fluoride electrode

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Gas Sensing Electrodes

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