The pH meter is an electrical apparatus used to measure the activity of hydrogen-ion in the solution. Calibration of pH meter with a minimum two buffer solutions, but if probable three buffer solution standards are generally used each time for the calibration of a pH meter. It needs to be regularly calibrated, although modern pH meter will hold calibration for one month.
Generally, three buffer solutions are used to calibrate the pH meter one of the buffers has a neutral i.e. pH 7.00 and the second buffer solution is slightly acidic pH i.e. pH 4.00 and another is basic i.e. pH 9.20. Preferred to compare the pH range in which the measurement of pH is to be taken. Meter gain and offset settings are adjusted frequently because the probe is placed alternately in two/three calibration parameters until the solutions get accurate readings. The modern apparatus has fully automated this process and needs to be immersed in only once or twice in each solution.
Before calibrating the pH meter, clean the electrode as follows.
Immerse the pH electrode in 0.1 M HNO3 or 0.1 M HCl for 15 minutes, followed by immersing in a storage solution for 30 minutes.
The calibration procedure for a pH meter:
Generally, three buffer solutions are used to calibrate the pH meter one of the buffers has a neutral i.e. pH 7.00 and the second buffer solution is slightly acidic pH i.e. pH 4.00 and another is basic i.e. pH 9.20. Preferred to compare the pH range in which the measurement of pH is to be taken. Meter gain and offset settings are adjusted frequently because the probe is placed alternately in two/three calibration parameters until the solutions get accurate readings. The modern apparatus has fully automated this process and needs to be immersed in only once or twice in each solution.
Before calibrating the pH meter, clean the electrode as follows.
Immerse the pH electrode in 0.1 M HNO3 or 0.1 M HCl for 15 minutes, followed by immersing in a storage solution for 30 minutes.
The calibration procedure for a pH meter:
- Select the buffer solutions which range the probable sample pH. The buffers should be pH 07.00, pH 04.00 and pH 09.20.
- Make sure buffer solutions are at room temperature. If the buffers are at different temperatures, temperature compensation is suggested and the sample should be measured at 250C.
- Rinse the electrodes with the help of distilled water and wipe with soft tissue paper.
- Keep the electrode in pH 07.00 buffer. Wait for a stable display. Set the instrument to the pH value of the buffer at the measuring temperature.
- Rinse the electrodes with the help of distilled water and wipe with soft tissue paper.
- Repeat the same process to the pH 04.00 and pH 09.20 buffer solutions as followed for the pH 07.00.
- Rinse the electrodes with the help of distilled water and wipe with soft tissue paper.
- Keep the electrode in the sample solution. While the display is stable, read the pH.
- Clean the electrode with distilled water and store in 3 M KCL/Saturated KCL/ pH 04.00 Buffer solution. (Do not store the pH electrode in deionized or distilled water).
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