A glass-electrode pH meter consists of a detector, indicator and reference solution. A brief description of each part follows:

■Detector(Glass electrode, Reference electrode, Temperature-compensation electrode, Combination electrode)

There is also a composite electrode, in which the glass electrode and reference electrode are integrated into one unit, and the combination electrode, into which all three of the above-mentioned electrodes are integrated into a single unit.

Glass electrode

Reference electrode

Temperature-compensation electrode

Combination electrode


The combination of a glass electrode and reference electrode can be thought of as a battery with high internal resistance. Thus, you cannot measure the difference in potential accurately if you connect it to an ordinary potentiometer (voltmeter) as-is. You need an amplifier with high input impedance. The indicator of the pH meter has such an such amplifier built in, and allows adjustment.

Explanation of Indicator

■Reference Solution

A reference solution must always be calibrated for the pH meter before measuring pH.

Explanation of Reference Solution

Next page  Calibration