14
352 050/REV A/03-03
8
3.5 Good Practice Guidelines
The types of electrodes are many and various. For the majority of tests carried out on aqueous
solutions, with a reasonable ionic strength; at ambient temperatures and with limited use in strongly
acidic or alkaline solutions, the standard glass or epoxy bodied combination electrode is ideal.
For other applications a more suitable pH/reference electrode pair may be required; details or
advice supplied on request.
The following general guidelines indicate the care and maintenance required for the three main
groups of electrodes (Combination, Reference and pH). For more detailed advice on specific
electrodes contact the electrode manufacturer.
1)
After use
Rinse thoroughly with deionised water
Short term storage
Immerse in pH 4 buffer (all types)
Long term storage
Fit wetting cap filled with 3M KCl adjusted to pH 4.
2)
Electrodes should be stored a) away from direct sunlight
b) in a vertical position
c) within their specified temperature range
3)
Always ensure the electrode is used within its specified temperature range. Degradation of
electrodes used above their specified temperature is rapid and irreversible.
4)
Ensure the level of fill solution is above the internal elements in the electrode and that this
level remains above the sample in use.
5)
DO NOT
touch the sensitive glass pH membrane or reference junction during use. Excess
droplets of solution may be removed by gently blotting with filter paper or tissue.
DO NOT
rub
the electrode as this may induce an electrostatic charge.
6)
Ensure no air bubbles are trapped at the bottom of the electrode. Removal of air bubbles is
possible by holding the electrode vertically and gently tapping the electrode body. Larger
bubbles may be removed by shaking the electrode in a downward direction.
7)
During use ensure the electrode is rinsed in deionised water between each measurement to
eliminate risk of contamination of solutions.
8)
Ensure that the side port/inlet if present is uncovered, especially during a long run of tests.
9)
For samples such as blood, serum or any measurements of Tris buffer solutions the junction
may become badly clogged. For these measurements it is recommended that the Tris buffer
electrode is used (924 030).
10) For applications associated with the measurement of food extracts, it is recommended that
the Food electrode is used (924 051). This will reduce the risk of blockage from fat proteins,
will be easy to clean and is perfect for measurements in agar media. This electrode is also
recommended for measurements where deposits on the electrodes are likely. The flat
surface is easy to clean and robust.
11) For low ionic strength applications the Environmental electrode (924 050) is recommended.
