A successful pH reading is dependent upon all components of the system being operational. Problems with any one of the three: meter, electrode, or buffer will yield poor readings.
Meters: A pH meter is a sophisticated volt meter capable of reading small millivolt changes from the pH electrode system. The meter is seldom the source of problems for pH measurements. Today pH meters have temperature compensation (either manual or automatic) to correct for variations in slope caused by changes in temperature. Microprocessor technology has created many new convenience features for pH measurement; autobuffer recognition, calculated slope and % efficiency, log tables for concentration of ions, and more.
Electrodes: A pH electrode consists of two half cells; an indicating electrode and a reference electrode. Most applications today use a combination electrode with both half cells in one body. Over 90% of pH measurement problems are related to the improper use, storage, or selection of electrodes.
Buffers: These solutions of known pH value allow the used to adjust the system to read accurate measurements. For best accuracy:
- Standardization should be performed with fresh buffer solutions.
- Buffers used should frame the range of pH for the samples being tested.
- Buffers should be at the same temperature as the samples. (For example: if all your samples are at 50°C, warm your buffers to 50°C using a beaker in a water bath.)
Buffer values are dependent upon temperature. The following table lists the NIST values of pH buffers at various temperatures.