To determine whether the pH electrode is damaged or needs to be replaced, a comprehensive assessment can be made through the following indicators:
I. Performance Parameter Testing
Youdaoplaceholder0 Abnormal calibration slope ‌
The theoretical slope should be 59.16 mV/pH (at 25℃). If the measured slope is less than 48 mV/pH or lower than 80% of the theoretical value (such as < 47.3 mV/pH), it indicates poor electrode sensitivity and it is recommended to replace it.
When calibrating at two points, the normal range of the slope should be 95% to 105%. If it is less than 90%, the performance is poor.
Youdaoplaceholder0 Zero-point potential drift ‌
In the pH 7.01 buffer solution, the zero-point potential should be stable at 0±30 mV (Ag/AgCl reference system). If it exceeds ±60 mV, replacement is required.
When switching to the mV mode to measure the pH 4.01 buffer solution, the normal potential should be 170±30 mV; otherwise, the electrode fails.
Youdaoplaceholder0 Extended response time ‌
The response time of the new electrode is usually less than 30 seconds. If it takes more than 1 to 2 minutes to stabilize in the buffer solution, it indicates a decline in performance.
Ii. Appearance and Physical Condition
Youdaoplaceholder0 Damaged sensitive film ‌
Cracks, scratches or obvious wear on the glass bulbs directly affect the H⁺ response.
Youdaoplaceholder0 The liquid junction is clogged ‌
There are crystals (such as KCl precipitation), contaminants blocking or electrolyte leakage at the liquid interface of the reference electrode.
Youdaoplaceholder0 Electrode lead fault ‌
Use a multimeter to detect short circuits/open circuits in the leads or poor contact.
Iii. Actual Measurement Performance
Youdaoplaceholder0 Reading is unstable ‌
The pH value in a static solution continuously drifts (such as fluctuation > ±0.1 pH) or cannot return to zero.
Youdaoplaceholder0 Poor repeatability ‌
When measuring the same solution multiple times, the deviation exceeds the allowable range (such as > ±0.1 pH).
Youdaoplaceholder0 Calibration failed ‌
Calibration cannot be carried out through standard buffer solutions, or the measurement error of known samples after calibration is significant.
Fourth, maintain historical and environmental factors
Youdaoplaceholder0 Duration of use ‌
Under normal conditions, the electrode life is 1 to 2 years. In high-temperature (> 60℃) environments, it may be shortened to 3 to 6 months.
Youdaoplaceholder0 Pollution situation ‌
The performance has not been restored after cleaning (such as soaking in 0.1Mol HCl or treating with a special cleaning agent).
Operation suggestions
Youdaoplaceholder0 Cross-validation ‌ : If electrode failure is suspected, the same sample can be measured with a new electrode for comparison.
Youdaoplaceholder0 Regular checks ‌ : It is recommended to calibrate weekly and keep track of the slope trend.