Brief tips on cleaning, storage, and maintenance of glass electrodes including references to appropriate solutions and immersion times
Storage of combined glass electrodes.
In the reference electrolyte, c(KCl) = 3 mol/L.
AgCl of the reference system dissolves as chloro complex better in solutions containing chloride than in water.
If a combined electrode is stored in water, AgCl can precipitate in the diaphragm.
Separate glass electrodes in distilled water.
Cleaning the diaphragm.
After measurements in media with low chloride concentration (precipitated AgCl in the diaphragm - dark-coloured diaphragm). Place the electrode overnight in concentrated NH3, rinse with water and renew the reference electrolyte.
After measurement in sulphide-containing media (Ag2S in the diaphragm - dark-coloured diaphragm).
Place the electrode in freshly prepared, slightly acidic 7% thiorea solution.
Then rinse with water and renew the reference electrolyte.
With organic contaminants: place the electrode for approx five minutes in chromosulphuric acid at 80C, then rinse thoroughly and the renew reference electrolyte.
If the above measures do not help carefully file down the diaphragm with a diamond nail file.
The out flowing electrolyte should be visible as a dark ring.
Care of the glass membrane.
After measurement in non-aqueous medias, soak the electrode in water between measurements.
After measurement in protein-containing media, immerse the electrode for several hours in a solution of pepsin in hydrochrloric acid (5% pepsin in c(HCl) = 0.1mol/L). Then soak thoroughly.
Regenerating of glass membrane.
Immerse the glass membrane either for one minute in a 10% solution of ammonium hydrogenflouride (NH4HF2) or for a few seconds in 40% HF.
After the etching rinse for approx ten seconds in an HCl solution (H20:conc.
HCl = 1:1).
Rinse the electrode with water and allow to stand for 24 hours in the storage solution.
