pH Calibration Procedure

pH Calibration Procedure and sample pH measurement

A pH meter requires calibrating to give accurate pH readings..
A pH meter calculates a sample's pH, based on the Nernst equation:
A 2 or 3 point calibration, using 2 to 3 different buffer solutions is usually sufficient for initial calibration as the meters electronic logic will calculate the pH values in between.
A 1 point calibration, with a buffer of a pH closest to the expected sample pH should be adequate once per day, but a 2 point calibration is recommended.

1. - Place enough of your selected pH buffer solution (pH 4.01 recommended) into a small beaker so that it can accommodate a small magnetic stirrer bar, electrode(s) and temperature probe (if fitted) (see diagram).

NOTE: Do not risk contamination of stock solutions (e.g. buffer solutions) by direct measurements of stock solutions.
2. - If your pH meter is not fitted with a temperature probe you will have to manually measure the temperature of your selected pH buffer with a thermometer and adjust the temperature control on your pH meter to the buffer's temperature.
If your pH meter does not automatically calculate the true pH of the pH buffer selected, determine the true pH from the pH Buffer Charts.
3. - Remove the protective cap(s) from the electrode(s) and rinse of the electrodes and temperature probe (if fitted) with distilled water using a squeeze bottle.

Dab dry the bottom of the glass bulb with a folded tissue paper.

NOTE: Do not wipe the glass bulb as it can produce interfering static charges or may permanently scratch the glass bulb affecting the electrode's response.
4. - Place electrode(s) and temperature probe into the selected pH buffer solution.

Make sure that the porous frit is covered with your solution (see diagram) and that the solution is being stirred manually or with your magnetic stirrer.

Then -

1. - Place enough of pH 7.00 buffer solutionsinto a small beaker so that it can accommodate a small magnetic stirrer bar, electrode(s) and temperature probe (if fitted) (see diagram).
2. - Follow steps 2. - 4. of the one (1) point calibration procedure.
3. - Follow steps 1. - 4. of the one (1) point calibration procedure (i.e. using the pH 4.01 buffer)
4. - Alternate between steps 2 & 3, directly above, until practically no adjustments are required
Note: always start with the pH 7.00 buffer for your first adjustment.

1. - Follow steps 1. - 4. of the two (2) point calibration procedure.
2. - Use a third pH buffer, whose pH value is as close as possible to the suspected pH of your sample, and follow the one (1) point calibration procedure .
Note: The third point is not used to calibrate your pH meter, but rather to confirm that the pH meter is calibrated correctly.

1. - Calibrate your pH meter.
2. - Secure accurately a representative sample and place enough of your sample solution into a small beaker so that it can accommodate a small magnetic stirrer bar, electrode(s) and temperature probe (if fitted) (see diagram).
3. - If your pH meter is not fitted with a temperature probe you will have to manually measure the temperature of your selected sample with a thermometer and adjust the temperature control on your pH meter to the samples temperature.
4. - Remove the protective cap(s) from the electrode(s) and rinse of the electrodes and temperature probe (if fitted) with distilled water using a squeeze bottle.

Dab dry the bottom of the glass bulb with a folded tissue paper.

NOTE: Do not wipe the glass bulb as it can produce interfering static charges or may permanently scratch the glass bulb affecting the electrode's response.
5. - Place electrode(s) and temperature probe into the your sample solution

Make sure that the porous frit is covered with your solution (see diagram) and that the solution is being stirred manually or with your magnetic stirrer.
6. - Record the pH reading along side the temperature it was measured at.