HND-R106
HND-R106 K09/0422
page 13
9.4 pH electrode
9.4.1
Design
In most cases so-called combination electrodes are
used. That means that all needed elements are
integrated in a single electrode (including reference
electrode).
Sometimes even a temperature sensor is integrated.
The picture on the right shows an electrode without
temperature sensor.
There are several design types for the diaphragm, but
generally said it is the connection between electrolyte
and the measured solution. A blockade or soiling of the
diaphragm is often the reason for the electrode’s
idleness and erratic behaviour.
The glass membrane has to be treated with care. The
hydrated gel layer forms on the surface of the glass
membrane, which is of highest importance for the
measurement. The electrode has to be kept wet to
preserve the hydrated gel layer (see below).
9.4.2
Further Information
PH-electrodes are wearing parts which need to be replaced, if the values required
can no longer be kept even after thorough cleaning and recovery or the electrode
signal gets to slow. The actual lifetime of an electrode depends highly on the
chemical or mechanical stress it is subjected to. Please take into account that
there are several materials that are in aqueous solutions aggressive to glass;
other chemicals may react with the KCl-solution in the electrode thus causing
blockades in the diaphragm.
Examples:
- with solutions containing protein, like they are used on the medical and
biological sector, KCI may result in the denaturation of the protein. - coagulated
varnish
- solutions with a relatively high concentration of silver ions
Any material depositing on the measuring membrane or the diaphragm will
influence the measurements and have to be removed at regular intervals. This
can be done by means of automatic cleaning equipment.
Electrodes have to be stored in a way that they are kept wet. An adequate
solution is to store them with suitable protective cap filled with KCl 3 M.
Please consider also the instructions in the electrode’s manual!
