YSI 5239 Dissolved Oxygen Probe - Manual (Page 13)

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(an insoluble solid and poor conductor of electricity)
accumulates at the anode, it begins to block the passage of
current in the electrolytic cell. The silver anode must be
cleaned periodically to prevent this thick layer of silver
chloride from reducing the sensitivity of the sensor.
T HE FUNCTION OF THE E LECTROLYTE
There are two main functions for the electrolyte:
1. Supply the chloride (Cl
-
) to the anode/reference
electrode for the counter reaction of the oxygen
reduction at the cathode.
2. Provide the ionic conduction of electricity inside the
cell, especially in the thin layer between the gold
cathode and the membrane.
Under normal operating conditions, such as measuring oxygen
around 100 %-air (8.27 mg/L) at 25° C, the strength of the
chloride concentration should last up to 500 hours before the
chloride becomes a limiting factor in the operation of the
oxygen sensor. 500 hours translates into about 62.5 working
days at 8 hours per day operation.