As a precision electrochemical sensor, the stability and measurement accuracy of pH composite electrodes directly affect the reliability of experimental or production data. Scientific maintenance methods can not only extend the lifespan of electrodes, but also avoid measurement errors or equipment damage caused by improper operation. The following systematically elaborates on the maintenance points of pH composite electrodes from the aspects of daily maintenance, storage management, calibration standards, usage precautions, and troubleshooting.

1、 Daily cleaning and maintenance

1. Instant cleaning after measurement

-Washing principle: Immediately rinse the electrode with a large amount of distilled water or deionized water after each use to remove residual samples. If the sample contains proteins, oils, or viscous substances, it should be soaked in a specialized cleaning solution (such as 10% ethanol solution or neutral detergent) first, and then rinsed with clean water.

-To avoid the spread of pollution: Do not wipe the surface of the electrode with paper towels or cotton cloth to avoid scratching the glass film or introducing fiber residue. Shake the electrode gently during cleaning and use water flow to wash away impurities.

2. Treatment of stubborn pollutants

-Protein attachment: If the electrode response slows down or drifts, it may be caused by protein adsorption. Soak in gastric protease solution (0.1g/L, pH 1.2-2.0) for 30 minutes, then rinse with clean water.

-Oil pollution: Gently wipe with diluted neutral detergent to avoid contact with glass film; If the oil pollution is severe, it can be soaked in low concentration ethanol (<10%) for a short period of time.

-Inorganic salt crystallization: Soak in dilute hydrochloric acid (pH ≈ 4) or oxalic acid solution, rinse immediately after dissolution.

3. Protection of sensitive components

-Glass film care: Avoid contact with strong acids (such as concentrated sulfuric acid, hydrofluoric acid), strong bases, or dehydrating solvents (such as acetone). If the glass film dries up, it needs to be soaked in a 0.1M KCl solution for activation first.

-Reference electrode maintenance: Check if the filling solution (3M KCl) of Ag/AgCl reference electrode is sufficient. If the liquid level drops, it needs to be replenished through the filling hole to avoid exposure and failure of the reference electrode.

2、 Storage and transportation management

1. Short term storage (days to weeks)

-Moisturizing preservation: Soak the electrode in a neutral solution containing 3M KCl (such as pH 7 buffer) to keep the glass film moist and prevent dehydration and aging.

-Avoid light and shock: The storage environment should be kept away from high temperatures, strong light, and magnetic fields to avoid thermal expansion or magnetization failure of internal components of the electrode.

2. Long term storage (over 1 month)

-Dry storage method: Use filter paper to absorb the surface moisture of the electrode, wrap it in an inert plastic film, and store it in a cool and dry place. It needs to be reactivated every two months.

-Taboo operation: Do not soak the composite electrode in distilled water for a long time, as it may cause leakage of the reference electrode solution or swelling of the glass film.

3. Transportation protection

-Use original protective covers to secure the electrodes and avoid glass film breakage caused by vibration. Before long-distance transportation, it is necessary to empty the bubbles inside the reference electrode and check the sealing.

3、 Calibration and Performance Verification

1. Selection of calibration buffer solution

-Standard buffer solution: Three standard buffer solutions, pH 4.01 (potassium hydrogen phthalate), pH 7.00 (phosphate), and pH 10.01 (borate), are selected to cover the pH range of the sample to be tested.

-Temperature compensation: Before calibration, a thermometer is needed to measure the temperature of the buffer solution. When manually inputting or automatically calibrating, the temperature compensation function is enabled.

2. Calibration operation specifications

-Sequential requirement: Calibrate from low to high pH (e.g. 4.01 → 7.00 → 10.01) to avoid high concentration H ⁺ contaminating the low pH buffer solution.

-Stability judgment: Each calibration needs to wait for the reading to stabilize (about 1 minute), and the value fluctuation should not exceed ± 0.02 pH before confirmation.

-Slope check: If the calibrated slope deviates from the theoretical value (within the range of 95% to 105%), it is necessary to check whether the electrode is aging or contaminated.

3. Calibration frequency

-Regular use: calibrate once a day before starting up; If measuring different batches of samples continuously, recalibrate every 4 hours.

-Special scenario: After measuring pH (<2 or>12) or high salt samples, calibrate immediately to eliminate interference.

4、 Precautions for use

1. Measurement operation specifications

-Mixing control: The magnetic stirring speed should not be too high to avoid shear force damaging the sensitive membrane; Suggested speed ≤ 500rpm.

-Response time: The time required for the electrode to reach 95% stable value is about 30 seconds to 2 minutes. In case of emergency, gently shake the electrode to accelerate balance.

-Temperature matching: The temperature difference between the sample temperature and the calibration buffer should be controlled within ± 5 ℃, otherwise recalibration is required.

2. Avoid mechanical damage

-Installation force: When inserting the electrode into the sample, it should be placed vertically and gently to avoid hitting the bottom of the container; Do not twist the glass part when holding the electrode.

-Connection protection: When plugging or unplugging the electrode plug, it is necessary to grip the insulation layer of the body to prevent pulling the wire from causing internal disconnection.

3. Special sample processing

-Volatile solution: When measuring volatile samples such as alcohol and ammonia, a sealed container should be covered to shorten the measurement time.

-Viscous sample: Rinse the electrode several times with physiological saline or diluent to ensure no residual adhesion.

5、 Common fault diagnosis and repair

1. Slow response or drift

-Possible reasons: glass film contamination, insufficient reference electrode liquid level, internal crystallization blockage.

-Solution: Follow the above cleaning steps to supplement or replace the reference electrode filling solution, and check if there are KCl crystals blocking the filling hole.

2. The reading deviation is too large

-Calibration verification: recalibrate and check the slope; If the slope is normal but the deviation persists, the electrical module of the instrument itself needs to be checked.

-Abnormal membrane potential: If there are scratches or corrosion on the glass membrane, the electrode needs to be replaced.

3. Leakage or unstable signal

-Insulation inspection: Use a multimeter to check the impedance of the electrode plug. If it is lower than 10M Ω, it may cause a short circuit due to moisture and needs to be dried.

-Shielding interference: Keep away from electromagnetic sources such as motors and high-voltage equipment, and ensure good contact with the grounding wire.

6、 Preventive maintenance and lifespan management

1. Regular deep maintenance

-Check the reference electrode filling solution monthly, soak the glass membrane in dilute hydrochloric acid every six months to remove scaling, and send it to a professional organization for sensitivity testing every year.

2. Life assessment

-Normal service life: The lifespan of the glass electrode is about 1-2 years, and the reference electrode can be replaced with a filling solution to extend its use; If special condition samples are frequently measured, the lifespan may be shortened to 6-12 months.

-Retired standard: When the slope after calibration is below 90% or the reading fluctuates by more than ± 0.1 pH, it is recommended to replace the electrode.