| pH measurement is usually done
with the use of a combination electrode. The combination electrode
is an electrode system formed by a glass sensing half-cell and
an internal reference half-cell. As the reference junction acts
as the medium of conductor between the reference electrolyte
and the sample to be measured, it must allow free movement of
electrons through the junction and into the sample.
A potential develops on the membrane surface when a pH electrode
comes into contact with a sample and its value varies with
the pH of the sample. This variation in potential is measured
in mV by a meter and is converted to direct pH values.
The selection of a suitable electrode depends on the types
of application.
Eutech Instruments has a comprehensive range of pH electrodes
for laboratory and process applications.
Electrode selection criteria includes:
1. Electrode Body
- Glass body is more resistant to corrosive materials
and solvents and withstands high temperatures beyond 100 ?C.
In contrast, plastic body electrodes are not recommended for
temperatures above 80 ?C but are more durable for rugged use.
As such the glass body electrode is most suited for routine
pH measurements for accuracy, high temperature and ease of
cleaning while the plastic body electrode is a good choice
for more rugged applications.
2. Reference Construction - Refillable electrodes
allows replenishment of reference electrolyte for repeated
usage. Conversely a sealed electrode usually has gel reference
electrolyte and replacement of electrode is necessary when
there is contamination.
The reproducibility and potential stability of the calomel
reference electrode is superior to those of the Ag/AgCl electrode
at a constant and relatively low temperature. The calomel
reference electrode has a temperature limitation of 80 ?C
and is recommended for clinical measurements and samples containing
protein, tris buffers and high purity water applications.
The Ag/AgCl reference electrode is good for general purpose
applications with a wide temperature range of -5 to 110 ?C.
3. Junction - The single junction electrode
is ideal for general purpose applications while the double
junction electrode is suitable for use with biological samples
and can be used to replace calomel reference electrodes.
4 Applications - General purpose electrodes
are economical combination electrodes ideal for general-purpose
applications in the lab or field. They have the impact-resistant
qualities of a plastic body. Electrodes provide a fast, stable
response and are ideal for prolonged use. Most electrodes
come in different lengths and diameters for specific applications.
Refillable electrode extends the useful life and is ideal
for measurement of viscous samples and pH samples with low
conductivity.
Electrodes (Size: 110 mm (L) x 12 mm (D)
are supplied with 1-metre cable and BNC connector and can
withstand temperatures up to 80 °C.
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