pH meter

pH electrode

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Encyclopedia of Analytical Chemistry: Applications, Theory and Instrumentation Amazon

Encyclopedia of Analytical Chemistry: Applications, Theory and Instrumentation

by Robert A. Meyers

rejuvenating pH electrode

Note: following procedures are a last resort. They may work, they may not. You may try them before throwing electrode away.

First of all - clean the electrode as described in electrode cleaning section, then:

If the electrode is still not working:

When the electrode has cooled, test the electrode as described in the testing electrode parameters section. This rejuvenating procedure is particularly effective with gel filled combination electrodes. Do not be concerned if a small amount of the gel protrudes through the reference frit during the boiling in nitric acid step. This is both acceptable and useful.

If this procedure does not result in a pH electrode that responds quickly and has a slope of 55 - 61 mV/pH unit, the electrode is unrecoverable and should be thrown away. Remember, the procedure was proposed for the electrode that was to be thrown away anyway.

Some manufacturers suggest the electrode may be reactivated by treating with a diluted solution of hydrofluoric acid followed by subsequent conditioning in electrolyte. Before considering the procedure, take into account that hydrofluoric acid is extremally dangerous! Safer (but still dangerous) approach can be to use some slightly acidic solution containing fluorides, like 20 wt% ammonium bifluoride, NH4HF2 - put glass bulb part of the electrode in the solution for a minute followed by 15 seconds bath in 6 M hydrochloric acid. Rinse the electrode well and soak for 24 hours in a pH buffer with pH < 7.