Calibration Of The Redox Electrode; Redox Measurement; Maintenance And Storage Of Ph / Redox Electrodes - Lovibond Tintometer SD 305 pH/ORP Mode D'emploi

5.6 Calibration of the redox electrode

It is not possible to calibrate redox electrodes, since the redox value, unlike the pH value,
is non-specific and depends on all the dissolved substances in a sample. In order to check
the sensor state of a redox electrode anyway, it can be immersed in a control solution with
a known redox value. If the absolute measurement value differs significantly from the redox
value of the control solution being used (± 40 mV), we recommend maintaining, cleaning or
replacing the electrode.

5.7 Redox measurement

The redox potential (also known as the ORP, or oxidation/reduction potential) represents
the oxidative or reductive effect of a sample and is always specified as a function of
the reference electrode being used in mV. Measurement is carried out frequently using
the commonly used Ag/AgCl reference electrodes. In the literature, however, the ORP
is also specified against the standard hydrogen electrode (SHE) in order to be able
also to compare measurement values when various reference electrodes are used.
The <Mode> button thus allows the redox value to be displayed either in mV or mV
Conversion
between mV/mV
Ensure that the parameter mV ( ) or mV
ment is carried out in the same way as the pH measurement (Chapter 5.5).

5.8 Maintenance and storage of pH / redox electrodes

Gel electrodes that cannot be topped up are wear parts, and their service life and measuring
accuracy depend significantly on their use, storage and care. Incorrect storage, as well as
particular samples, such as those with aggressive chemicals, high potential for contamination
and high temperature, can shorten the life expectancy of the electrode to a few months or
even weeks. Samples with very poor conductivity – that is, a very low salt content – prolong
the electrode's response time. Electrodes undergo a natural ageing effect, which leads to
a shift in the electrode's offset point and slope. To slow down the ageing process and
to preserve the associated performance and accuracy, please observe the following:
Never store pH and ORP electrodes in distilled water or solutions with a pH > 8!
!
This would result in a drastic reduction in their service life.
To slow down the ageing process of the pH and ORP electrodes, we recommend
storing them in a suitable storage solution when not in use. Solutions with 3 M
KCl are particularly suitable for this purpose. Before immersing the electrode in
the storage solution, we recommend rinsing it carefully with distilled water.
50
mV
Display of the redox value vs. Ag/AgCl (3 M KCl)
mV Display of the redox value vs. SHE
H
ORP vs. Ag/AgCl (3 M KCl) = ORP vs. SHE + 210 mV at
25°C
H
( ) is selected in the display. The redox measure-
H
SD_305_pH/ORP_1 04/2021
.
H