Repair Methods for pH Electrodes
The "failure" of a pH combination electrode shows symptoms including reduced sensitivity gradient, slow response and poor repeatability of readings. It may be caused by the following three factors, and users can carry out proper repairs:
① Contamination of the electrode bulb and liquid junction. Carefully remove contaminants with a fine brush, cotton or toothpick. The protective cap on the head of some plastic-body electrodes can be unscrewed for easier cleaning. In case of heavy contamination, clean with detergent in accordance with the method specified in Item 8.
② Contamination of the external reference solution. For refillable electrodes, draw out all the old external reference solution with a syringe. Prepare fresh 3.3 mol/L or saturated KCl solution and refill it. Note that the first and second batches of filled solution should be drawn out again to thoroughly rinse the inner cavity of the electrode.
③ Aging of the sensitive glass membrane. Immerse the electrode bulb in 0.1 mol/L dilute hydrochloric acid (dilute 9 mL hydrochloric acid to 100 mL with pure water) for 24 hours, rinse with pure water, then soak in electrode soaking solution for another 24 hours. For severe passivation, immerse the electrode tip in 4.5% hydrofluoric acid solution for 3~5 seconds (solution preparation: dilute 4 mL hydrofluoric acid to 100 mL with pure water). Rinse with pure water, then soak in electrode soaking solution for 24 hours to restore its performance.
