Calibrating is necessary to ensure the meter’s display produces accurate
readings. Calibrating is conducted using standard pH buffer solutions
which are made to internationally agreed recipes. These are stable
solutions that possess a specific pH value.
It is essential to calibrate using at least two pH buffers. These need to
differ in pH by at least three pH units over the pH range being used.
pH buffer 4.0 and 7.0 are the
ideal calibration standards. Some manufacturers claim that their pH meters
require calibration using only pH buffer 7.0. Professional practice
however, stipulates using two buffers because this will confirm or
otherwise that the correct calibration “slope” is being obtained i.e. that
both the electrode and meter are ranging correctly.
Use experience as a guide for the required calibration frequency.
Refer to your meter's instructions for the calibration procedure. To
ensure the calibration procedure is successful, note the following:
Step 1. To prevent contamination of
the stock pH buffers, decant a small portion into a small, narrow
container for the calibration procedure. Discard this once used.
Step 2. Rinse the electrode in
distilled water and gently shake off the excess water prior to placing it
in the pH buffer solution.
Step 3. After calibrating, remove the
electrode from the pH buffer solution, rinse with distilled water and
return it to the