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Since the resistance of the pH electrode is in the range of 50 – 200 MΩ, the current across the
membrane is in the pico Ampere range. Large currents can disturb the calibration of the electrode
for many hours.
The pH electrode’s life also depends on the temperature. If constantly used at high temperatures,
the electrode life is drastically reduced.
Typical Electrode Life
Ambient Temperature 1 – 3 years
90 °C (194 °F) Less than 4 months
120 °C (248 °F) Less than 1 month
The resistance of glass electrodes partially depends on the temperature. The lower the temperature,
the higher the resistance. It takes more time for the reading to stabilize if the resistance is higher.
TEMPERATURE CORRELATION FOR pH SENSITIVE GLASS
Alkaline Error
High concentrations of sodium ions interfere with readings in alkaline solutions. The pH at which
the interference starts to be significant depends upon the composition of the glass. This interference
is called alkaline error and causes the pH to be underestimated.
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