PH-sensitive glass membrane

Figure 21-9a shows a typical cell for measuring pH. The cell consists of a glass indicator electrode and a saturated calomel reference electrode immersed in the solution of unknown pH. The indicator electrode consists of a thin, pH-sensitive glass membrane sealed onto one end of a heavy-walled glass or plastic tube. A small volume of dilute hydrochloric acid saturated with silver chloride is contained in the tube. (The inner solution in some electrodes is a buffer containing chloride ion.) A silver wire in this solution forms a silver/silver chloride reference electrode, which is connected to one of the terminals of a potential-measuring device. The calomel electrode is connected to the other terminal. 

Figure 2 Schematic representation of the hydrated layer of a pH-sensitive glass membrane electrode. I, internal reference solution II, external (sample) solution of unknown pH.

FIGURE 5.4 Schematic of a combined pH/silver-silver chloride sensor. (1) Ag/AgCl reference electrode, (2) salt bridge, (3) filling hole, (4) reference electrode solution, (5) internal buffer solution, (6) Ag/AgCl internal electrode, (7) pH-sensitive glass membrane, and (8) Pt wires. 

A conventional pH electrode contains a pH-sensitive glass membrane. Thus, a number of efforts were put forward in order to replace the glass membrane with other pH-sensitive materials such as metal oxides, polymers, and carbon nanotubes. 

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