Problems Related to pH Meter Maintenance
① Storage of pH Glass Electrodes Short‑term storage: Store in pH = 4 buffer solution. Long‑term storage: Store in pH = 7 buffer solution.
② Cleaning of pH Glass Electrodes Contamination on the glass bulb of a glass electrode may increase the electrode response time. Remove contaminants with CCl₄ or soap solution, then immerse the electrode in distilled water overnight before reuse. In case of heavy contamination, soak the electrode in 5% HF solution for 10–20 minutes, rinse thoroughly with water immediately, then immerse it in 0.1 N HCl solution overnight before reuse.
③ Treatment for Aging Glass Electrodes Aging of glass electrodes is associated with gradual structural changes in the glass membrane. Old electrodes feature slow response, high membrane resistance and low slope. Etching away the outer glass membrane with hydrofluoric acid can often improve electrode performance. If the inner and outer glass membranes are regularly etched by this method, the service life of the electrode can be nearly unlimited.
④ Storage of Reference Electrodes Silver‑silver chloride electrodes are best stored in saturated potassium chloride solution. The high‑concentration potassium chloride solution prevents silver chloride precipitation at the liquid junction and keeps the liquid junction in working condition. This method is also applicable to the storage of combination electrodes.
⑤ Regeneration of Reference Electrodes Most problems of reference electrodes are caused by liquid junction blockage. The following methods can be used for troubleshooting:
(1) Liquid junction soaking: Prepare a mixture of 10% saturated potassium chloride solution and 90% distilled water, heat it to 60～70℃. Immerse about 5 cm of the electrode tip in the solution for 20 minutes to 1 hour. This method can dissolve crystals at the electrode tip.
(2) Ammonia soaking: When the liquid junction is blocked by silver chloride, soak it in concentrated ammonia water. Rinse and empty the internal filling solution of the electrode, then immerse the electrode tip in ammonia water for 10～20 minutes. Do not allow ammonia water to enter the electrode interior. Take out the electrode, rinse with distilled water, refill the internal filling solution and reuse.
(3) Vacuum method: Fit a hose over the liquid junction of the reference electrode. Use a water aspirator to draw part of the internal filling solution through the liquid junction to remove mechanical blockages.
(4) Boiling the liquid junction: Immerse the liquid junction of silver‑silver chloride reference electrode in boiling water for 10～20 seconds. Note: The electrode must cool down to room temperature before the next boiling treatment.
(5) If all the above methods fail, mechanical polishing with sandpaper can be adopted to remove blockages. However, sand particles generated during polishing may get stuck in the liquid junction and cause secondary blockage.
