Advances in Ion Selective Electrodes(ISE)


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Advances in Ion Selective Electrodes(ISE)

  2. 2. Preview1) Introduction to Ion Selective Electrodes,ISE2) Composition of ISE(Glass Membrane Electrode,Solid StateElectrode,Liquid Membrane Electrode,Gas Sensing Electrode)3) Parameters of ISE(sensitivity,selectivity,detection limit andresponse time)4) Potentionmetric measurements of ISE(in vivo, on line,on site)5) The Recent advance(application of ISE)
  3. 3. Ion selective electrodes(ISE)-An ion-selective electrode (ISE), also known as a specific ionelectrode (SIE), is a transducer (or sensor) that converts the activity ofa specific ion dissolved in a solution into an electrical potential, whichcan be measured by a voltmeter or pH meter.-Several types of sensing electrodes are commercially available whichare Glass Membrane Electrode, Solid State Electrode, LiquidMembrane Electrode,Gas Sensing Electrode
  4. 4. • 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 = EISE - ERef
  5. 5. TYPES OF ION SELECTIVE ELECTRODE (ISE) •Glass Membrane Electrode •Solid State Electrode •Liquid Membrane Electrode •Gas Sensing Electrode
  6. 6. GLASS MEMBRANE ELECTRODE• Glass electrode are responsive to univalent cations ( H+ , Na+)• The selectivity for this cation by varying the composition of a thin ion sensitive glass membrane.• Example: pH electrode - used for pH measurement - used as a transducer in various gas and biocatalytic sensor, involving proton generating or consuming reaction.
  7. 7. pH electrode•Glass membrane manufactured from SiO2 with negativelycharged oxygen atom.•Inside the glass bulb, a dilute HCl solution and silver wirecoated with a layer of silver chloride.•The electrode is immersed in the solution and pH ismeasured.
  8. 8. SOLID STATE ELECTRODE Solid state electrode are selective primarily to anions. It may be a homogenous membrane electrode or heterogeneous membrane electrode. Homogenous membrane electrode: ion-selective electrodes in which the membrane is a crystalline material (AgI/Ag2S).
  9. 9.  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
  10. 10. 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.
  11. 11.  Example: Ion Exchanger Electrode •The polymeric membrane made of PVC to separate the test solution from its inner compartment. •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.
  12. 12. 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.
  13. 13.  The change is detected by a combination pH sensor within the housing. This type of electrode does not require an external reference electrode.
  14. 14. Parameters of ISE  Sensitivity  Selectivity  Detection Limit  Response Time
  15. 15. Nikolsky-Eisenman equation,Where RT.ln10/F-Sensitivity(S) kxy-selectivity coefficient ax-activity of the ion, X ay-activity of the interfering ion, Y zx-charge of the primary ion, X zy-charge on the interfering ion, Y The ‘constant’-E0
  16. 16. Selectivity An electrode used to measure primary ion X selectively may also slightly responds to interference ion Y. Selectivity coefficient, kxy,is used in ISE to distinguish the ion X from ion Y in the same solution. kxy is not constant and depends on several factors including the concentration of both elements, the total ionic strength of the solution, and the temperature. The value of kxy, is defined by the Nikolsky-Eisenman equation:  The smaller the value of kxy ,the greater is the electrode’s preference for the primary ion, X.
  17. 17. Sensitivity Ability to detect primary ion at the lower concentration. Theoretical value of S=59mV,represents 100% sensitivity. The value of S varies with kxy small value of kxy means that the electrode is more sensitive to primary ion,X instead of interfering ion,Y.
  18. 18. Detection limit Defined by the intersection of the two extrapolated linear parts of the ion-selective calibration curve. LOD ~ 10-5-10-6 M is measured for most ISE. Observed LOD is often governed by the presence of other interfering ions or impurities. Metal buffers can be used to eliminate the effects which lead to the contamination of very dilute solutions. May reduce LOD to 10-10 M.
  19. 19. Response time From the time the ISE and a reference electrode are dipped in the sample solution (or the time at which the ion concentration in a solution in contact with ISE and a reference electrode is changed ) to when the potential of the cell becomes equal to its steady-state value within 1 [mV] or has reached 90% of the final value (in certain cases also 63% or 95%). The response time usually increases with decreasing determinand concentration
  20. 20. Time constant of Rate of the charge- the measuring Determinand transfer reaction instrument diffusion through the across the hydrodynamic layer membrane/solution interface, which results in charging of the electrical double layer at this interfaceRate of the exchangereaction between the Factors determinand in the influence membrane and an interferent in the response time Dissolution of the analyte membrane-active component in the analyte Establishment of the Interferent diffusion potential diffusion in the across the membrane membrane
  22. 22.  Meanings: 1) on-line : being in progress now. 2) on-site : taking place or located at the side. 3) in vivo : within a living organism.
  23. 23.  ISE have been widely used as detectors in high-speed automated flow analyzers such as air-segmented or flow injection systems for the high-speed determination of physiologically important cationic or anionic electrolytes in body fluids. Example of flow injection determination of physiologically potassium in serum. Several designs of low-volume potentiometric flow detectorshave been reported. Flow-through potentiometric cell design
  24. 24. Potentiometric microelectrodes are very suitable for in vivo real timeclinical monitoring of blood electrolytes, intracellular studies, in situenvironmental surveillance or industrial process control. For exampleSimon’s group described the utility of a system for on-line measurementof blood potassium ion concentration during an open-heart surgery. Miniaturized catheter-type ISE sensors such as implantable probe represent the preferred approach for routine clinical in vivo monitoring of blood electrolyte. Diamonds group developed an array of miniaturized chloride, sodium, and potassium ISEs for point-of-care analysis of sweat in connection to non- invasive diagnosis of cystic fibrosis. Miniaturized catheter-type ISE sensor
  25. 25. Recent Advancement of Ion Selective Electrode (ISE)
  26. 26. Agriculture and Fishery Pollution Control-Soil and fertilizer for -pH of acid rain, soil, surface waterNitrate, Ammonium, -Contamination of surface water Potassium to optimize the use of and ground water with ammoniumfertilizer. and nitrate-Dissolved Oxygen and pH in ponds -Contamination of waste water withfor Cyanide, Cadmium, Mercury and fish breeding. CopperIndustrial Production Food and Quality Control-Salinity and pH of Boilerfeed Worldwide -Nitrate and Nitrite in meat and application vegetables water -Chloride, Sodium, Nitrate and-Cyanide in plating baths Nitrite in-Process (specific ions) baby food. -Cadmium in fish Medical Diagnosis and Hygiene Control -Potassium in urine -Contamination in various ions.
  27. 27. Advantages of Ion Selective Electrode (ISE) Technique When compared to many other analytical techniques, Ion- Selective Electrodes are 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. They are particularly useful in applications where only an order of magnitude concentration is required, or it is only necessary to know that a particular ion is below a certain concentration level.
  28. 28.  They are invaluable for the continuous monitoring of changes in concentration for example in potentiometric titrations or monitoring the uptake of nutrients, or the consumption of reagents. They are particularly useful in biological/medical applications because they measure the activity of the ion directly, rather than the concentration. ISEs are one of the few techniques which can measure both positive and negative ions. They are unaffected by sample colour or turbidity. ISEs can be used in aqueous solutions over a wide temperature range. Crystal membranes can operate in the range 0 C to 80 C and plastic membranes from 0 C to 50 C.
  29. 29. Surface Plasmon Resonance (SPR) Based on immunosensors for detection and monitoring of low-molecular- weight analytes of biomedical, food and environmental fields. SPR is a surface sensitive optical technique for monitoring biomolecular interactions occurring in very close vicinity of a transducer (gold) surface, and that has given it a great potential for studying surface-confined affinity interactions without rinsing out unreacted or excess reactants in sample solutions. It allows real-time study of the binding interactions between a biomolecule (antibody) immobilized on a transducer surface with its biospecific partner (analyte) in solution without the need for labeling the biomolecules by exploiting the interfacial refractive index changes associated with any affinity binding interaction. In general, an SPR immunosensor is comprised of several important components: a light source, a detector, a transduction surface (usually gold-film), a prism, biomolecule (antibody or antigen) and a flow system.
  30. 30. • The transduction surface is usually a thin gold-film (50–100 nm) on aglass slide optically coupled to a glass prism through a refractive indexmatching oil. In addition to gold, several metals can be used includingsilver, copper and aluminium. However, gold is highly preferred due to itschemical stability and free electron behaviour.
  31. 31. Thank you for your attention