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4.5.7. The sensitive glass bulb in the front of combination electrode should not touch with
hard things, any broken and rough will make the electrode invalidity. Before and after
measuring, the electrode should be washed with purified water, and dry electrode
after washing, don’t clean glass bulb with tissue for it will effect stability of electrode
potential and enlarge response time. The electrode should be washed many times for
removing the sample stuck on the electrode, or wash with suitable solvent then clean
the solvent with purified water after measuring sticky sample.
4.5.8. An electrode be used for a long time, or measured solution which contains a polluting
solute easily for the sensitive bulb, or a substance resulting in jam at the junction, the
electrode will be getting passivated, its sensitivity will decrease and its response is
getting slow, the reading are not correct. It could adopt the following method for
various cases:
(a) The glass bulb is contaminated and aging: Put the electrode into 0.1mol/L dilute
hydrochloric acid (Preparation: diluted 9mL hydrochloric acid to 1000mL with
purified water) for 24h. Rinse it with purified water, then dipped it into the electrode
dipping solution for 24h. If the passivation is serious, then user can also put the bulb
of electrode into 4% HF (hydrofluoric acid) or the electrode activation solution for 3
to 5 seconds, rinsing it with purified water, and dipped it in the electrode soaking
solution for 24h to renew it.
(b) Wash for contaminated glass bulb and junction: (For reference)
Contamination
Abluent
Inorganic metal oxide
diluted acid less than 1mol/L
Organic lipidic matter
dilute washing (weak alkaline)
Resin macromolecule matter
dilute alcohol, acetone, ether
Proteinic haematocyte sediment
Acidic enzymatic solution (such as dried yeast)
Kinds of paint
dilute bleacher, peroxide
