Why do pH electrodes need to be replaced?

All pH electrodes are essentially an electrolytic battery that measure very small ionic electrical charges. Just as batteries lose their electrical charge so too do pH electrodes. The typical lifespan of a pH electrode can be anywhere from six months to 24 months depending upon design and how well they are cleaned and maintained as well as to what substances they are exposed to. In some aggressive chemicals an electrode might last only a few weeks such as Hydrofluoric Acid.

In addition to pH electrodes being a type of battery they also have a porous reference junction which can become chemically contaminated. A contaminated electrode if it cannot be successfully cleaned with a solvent or electrode cleaning solution and then rinsed in deionized water so that it again functions correctly must be replaced.