Page 52 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202
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It responds directly to change in activity of metal ion

Examples:

- Silver electrode   Ag+ + e− ↔ Ag (s)                   E0 = +0.79 V
          Ag /AgNO3

Metal electrode solution to be measured

It responds to the activity of Ag+

Eind = E0 − 0.059 log 1
                     1 [Ag+]

Eind = 0.79 V + 0.059 log [Ag+]

3- Electrode of the second kind: (for anions)

- A metal wire coated with one of its salts precipitate.
- It responds to the activity of anion that form sparingly soluble

   precipitate or stable complexes with metal ion

Example Ag/AgCl (Silver metal coated with AgCl paste)
It is used to measure [Cl−] (eg KCl solution)

AgCl(s) + e− ↔ Ag(s) + Cl−               E0 = +0.222 V

Eind = E0 Ag/AgCl − 0.059 log [Cl−]

           Membrane Electrodes

   1. Sensitive to ionic species --- Ion-Selective Electrodes
   2. Sensitive to molecular species

Example of Ion-Selective Electrodes

   Glass membrane electrode

It is sensitive to changes in H+ concentration --- used to
measure pH

          Theory of the glass membrane potential

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