Page 58 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202
P. 58

Properties of pH meter

- This electrode is not affected by the presence of oxidizing or
   reducing agents

- Operative over a wide pH range
- Responds fast and functions well in physiological systems

Types of Errors in the Measurement of pH
Alkaline Error

In basic solution, at high pH > 9, glass electrodes respond to the

                                                    ++

concentration of both H and alkali metal ions (mainly Na ) ---
negative error --- the measured pH values are lower than the true
values
Error negligible at pH less than 9

Acidic error

In solutions of pH < 0.5, the pH readings tend to be somewhat high
---- positive error ---- it can be attributed to the saturation effect that

                                                                                                                                    +

occurs when all surface sites on the glass are occupied with H ---

                                                                                                                                          +

the electrode no longer responds to further increase in H
concentration.

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