A pH meter is a precision measuring device that requires proper use and good
maintenance.
The principle of a pH meter:
There is always a reference electrode and an indicator electrode. The reference electrode has a set
value and thus provides a fixed reference against the indicator electrode. The indicator electrode can
be easily distinguished from the reference electrode. The indicator electrode very often takes the form
of a glass bulb (globe). In certain other models this is a window. This little glass bulb is very vulnerable
and will have to be protected against all kinds of influences. Only fluids may come into contact with it.
So do not use fingers, tissues, paper, brushes or the like. The indicator electrode is positioned in an
electrolytic environment.
The disadvantage of the pH meter is that unfortunately the electrodes are not permanent. Many elec-
trodes are spent after only one year. The useful life is determined not only by the number of times of
use but also by the way in which they are used and maintained.
The better you protect your meter the longer its useful life.
Some tips:
- Always rinse the electrode in demineralized water (before and after use). Make certain that no resi-
dues adhere to the electrode.
- Always keep the electrode in some preserving fluid (in the phial, on the sponge)
- Never keep the electrode in demineralized water.
- If crystals form (after long storage without use), rinse with demineralized water and leave to steep
one day in preserving fluid.
- If the measured value appears slowly this indicates reduced electrode activity.
- If you have a refillable electrode that you wish to refill, first bleed the electrode. The electrolyte is no
longer fit for purpose and will have to be replaced. So always replace all of the electrolyte. After refill-
ing allow the meter to stabilize for a few hours and then recalibrate.
- A temperature above 50°C is not good for the electrode and reduces useful life.
- The reason for the repeated recalibrations of a pH meter has to do with the constantly reduced activ-
ity of the electrode.
- Always start calibration with a pH 7 buffer fluid. Follow with pH 4. When changing the buffer fluid,
always rinse thoroughly with demineralized water.
• Calibrate weekly after daily use
• Calibrate monthly after weekly use
• Calibrate each time after one-off use
• Keep the buffer fluids preferably in a refrigerator and allow them to reach room temperature be-
fore use.
- Do not reuse used buffer fluid; this will be contaminated by, e.g., exposure to air.
- Never place the electrode directly in the flask with the buffer fluid; better to decant a little into a
small container.
- Change electrodes:
• if calibration is no longer possible
• if refilling (if applicable) is no longer possible
• if cleaning does not help
• if the electrode is damaged
