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351 050/REV B/09-06
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The voltage developed by each individual pH electrode in the presence of a known hydrogen ion
concentration is theoretically predictable, but in practise deviations from the theoretical value can be
expected. These deviations will change slowly during the life of an electrode. It is therefore essential
to routinely calibrate the system using solutions with a known and constant pH value. These
solutions are called buffers.
3.3 Preparation of Buffer Solutions
Care must be taken in the preparation of all buffer solutions. The correct quantity of distilled or
deionised water should be used when preparing the solutions. For accurate and repeatable results
it is essential to follow the manufacturers instructions carefully.
3.4 Solution Temperature Values
The value of all buffer solutions varies with solution temperature. For accurate calibration of
electrodes using buffer solutions, it is necessary to measure the temperature of the buffer solution
being used. The unit should then be calibrated to the corrected pH value. Manufacturers of buffer
powders and solutions will provide a table of values at varying temperatures for their buffers.
Note:
Buffer solutions will contaminate with exposure to air and should be stored
in airtight containers when not in use. Used solution should be discarded and
not returned to the container as this will cause contamination.
For best results fresh solutions should be prepared prior to calibration.
