indicator electrode

Dear sam jha

Indicator Electrodes

There are 3 types of indicator electrodes:

• Class I (primary) electrode: metal immersed in solution containing the ion/molecule of interest:
   

Most common of these are Pt, carbon or Au electrodes

• Class II (secondary) electrode: an electrode in direct contact with an anion with which its ion forms a precipitate or a stable complex ion so that the potential response measures the inactive species:

  Here, the determination of the chloride ion is facilitated by the formation of a stable complex or precipitate such as AgCl. An example of this is the silver-silver chloride reference electrode.

• Class III (tertiary) electrodes: an electrode in direct contact with a cation with which its ion forms a precipitate or a stable complex ion so that the potential response measures the inactive species, for example a Hg electrode in the presence of EDTA, with Ca-EDTA added:

  
  

  Y = EDTA anion

  Here, the Hg electrode has become a Class III electrode for the detection of Ca+ ion.

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