Page 55 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202
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-Internal reference electrode: Ag wire coated with AgCl + internal
filling solution, 0.1 M HCl --- its potential is necessarily constant
and is set by the concentration of HCl
pH glass electrode
Glass electrode is an indicator
electrode which is sensitive to H+
Eind = Eb + E Ag/AgCl
(Eb = K1 − 0.059 pH, EAg/AgCl is a constant based on [Cl- ] )
Eind = K2 − 0.059 pH (K2 merges K1 and EAg/AgCl)
pH meter (pH combination electrode)
Potentiometric Cell for measuring pH
The cell for measuring pH "galvanic" consists of:
1- A glass indicator electrode (glass pH sensitive membrane +
internal ref electrode)
2- Saturated Calomel electrode (external ref electrode),
immersed in the solution of unknown pH
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