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5.1.3 Design
1. Coaxial cable
2. Reference electrode
3. Measuring electrode
4. Refill opening
5. Electrolyte
6. Internal buffer
7. Diaphragm
8. Glass membrane / source layer
The diaphragm, which establishes a connection between the electrolyte and the liquid
to be measured, can be designed in different ways. Clogging or soiling of the dia-
phragm is a frequent cause of a malfunctioning or sluggish electrode. Always handle
the glass membrane with extreme care. The so-called source layer forms there. This
is crucial for the measurement and must always be kept moist.
There are also electrodes with integrated temperature sensors.
5.1.4 Further information
A pH electrode is a wear part. If the signal is very slow or the required values are no
longer observed after careful cleaning and possible regeneration, the electrode must
be replaced. When using the electrodes, be aware that various substances in aqueous
solutions can corrode glass and that chemicals can produce a chemical reaction with
the KCl solution in the electrode, which can result in blockage of the diaphragm.
– In solutions that contain proteins, such as for measurements in medical and biolo-
gical applications, KCl can cause denaturation of the protein.
– Coagulated paints
– Solutions that contain high concentrations of silver ions
Substances that accumulate on the glass membrane or the diaphragm affect the
measurement and must be removed regularly. This can be achieved for example with
automatic cleaning systems.
5.1.5 Choosing a pH electrode
The GE 114 WD or GE 100 can be used for most applications. However, some areas
of application require special electrodes.
– GE 100 BNC is a universal electrode with two ceramic diaphragms and liquid elec-
trolyte.
– GE 101 BNC is preferably used for small sample amounts. It comprises a glass
electrode with two ceramic diaphragms and liquid electrolyte.
– GE 104 BNC is preferably used for measurements in low-ionic media, such as
rainwater, aquarium water and deionised water.
– GE 114 WD is a universally applicable, durable and low-maintenance gel elec-
trode with Pellon diaphragm. It can be used for measurements in drinking water,
swimming pools, aquaria and slightly contaminated waste water.
– GE 117 BNC is a temperature-compensated gel electrode with two ceramic dia-
phragms and PH 13.5 cable screw coupling.
