Standardizing the pH Meter

A pH meter may be standardized as follows:

1. Rinse electrodes with distilled (or deionized) water and blot dry.
2. Place electrodes in pH standard buffer solution.
3. Adjust pH meter temperature dial to the temperature of the standard solution.
4. Turn pH meter to "operate."
5. Adjust pH meter to the pH value of the standard, using the "standardize" control. THE pH METER IS NOW STANDARDIZED.
6. Turn pH meter to "standby".
7. Remove electrodes from standard and rinse with water.

The pH Measurement Procedure

Once the pH meter is standardized, the measurement procedure is as simple as this: 1. Rinse electrodes with distilled (or deionized) water and blot dry.
2. Place electrodes in test solution.
3. Adjust pH meter temperature dial to the temperature of the test solution.
4. Turn pH meter to "operate."
5. Read the pH of the test solution on the pH meter directly.
6. Turn pH meter to "standby."
7. Remove electrodes from test solution and rinse with water.

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Redox Measurements

The measurement of the oxidation-reduction potential of a solution is commonly called a redox measurement. This measurement gives an indication of oxidizing or reducing power of a solution. Since a pH meter is also a very good voltmeter, it can be used in making redox measurements. The sensing electrode used in this measurement is usually platinum, although gold and silver have been used for special purposes. The reference electrode is the same as that used in pH measurements. The electrode potential is usually expressed in millivolts ( mV ). Thus, most pH meters have a ( mV ) scale, as well as a pH scale. Also, since the temperature coefficient varies with the particular redox couple being measured, the temperature control is deactivated during the ( mV ) measurement.

plon Measurements

In recent years electrodes similar to the pH electrode but specific for other ions have been developed. These include electrodes for ammonia, chloride, cyanide, nitrate and sulfide, to name a few. These electrodes may be used in combination with a reference electrode with any modern pH meter. The meter should be standardized in a solution of known plon of the ion of interest, just as in the pH standardization. The plon of a test solution can then be read directly on the meter as in the pH measurement.

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