The Definitive Guide to pH Probes:
Part 6 "Poisoned Reference Electrode"

The Definitive Guide to pH Probes: <br>Part 6 "Poisoned Reference Electrode"
Authored By TPS Website

Did you know pH Sensors can fail when the reference electrode stops working properly due to reactions with certain ions? The Ions are formed when electrolytes dissolve in water, separating into cations and anions. Cations are atoms that have lost electrons, while anions are atoms that have gained electrons. Ions are attracted to each other by opposite charges, and they form ionic bonds.

Ions such as chrome, iron, cyanide, sulfide, lead, bromide, iodide, bisulfite and ammonia can all cause reactions that damage the reference. The reactions may initially be difficult to detect, but when the Silver Chloride on the electrode is used up, the offset of the reference will change dramatically and the sensor will need replacement. 

There are some designs that help sensors last longer when testing in samples that contain these ions and other contaminants. Sensors with double or even triple junctions can greatly extend the useful life of the sensor. For process applications, differential sensors may also be suitable.

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