Causes of Unqualified Calibration and Calibration Operation Steps for the Ion Meter Electrode of Lianhua Technology

Some customers encounter issues during calibration of Lianhua Technology ion meters (models LH-E4ISE and LH-ISE310), including unchanged potential values, severe potential fluctuation and instability, failed blank potential qualification, abnormal slope calibration, and biased measurement results. Follow the inspection and calibration procedures below for troubleshooting:

I. Preparations & Electrode Inspection
Check for air bubbles inside the electrode. If bubbles exist, gently shake the electrode to remove them; otherwise, calibration will fail even if activation and calibration steps are performed correctly.
For new electrodes, calibration failures are frequently caused by crystals clogging the liquid junction at the electrode tip. Shake the electrode gently several times prior to activation and calibration to resolve this issue. If the problem persists, place the electrode in a beaker filled with pure water and sonicate it in an ultrasonic cleaner for 5–10 minutes for effective unclogging.
Certain electrodes require filling electrolyte solution. The filling hole must remain open throughout calibration and measurement. Ensure no continuous air bubbles remain after refilling. Maintain the electrolyte volume at over two-thirds of the electrode interior (slightly below the filling port) during operation, and replenish electrolyte in a timely manner as needed.

II. Electrode Activation
New electrodes must undergo activation before initial use. Electrodes idle for more than half a month also require reactivation. Prepare standard solutions at a concentration of 50 mg/L corresponding to the target ion for activation. Adhere strictly to the specified activation duration stated in the manual; shortened activation time will result in unstable potential and calibration failure.

III. Standard Solution Preparation & Calibration
Prepare two calibration standard solutions with a 10-fold concentration difference (e.g., 10 mg/L and 100 mg/L). Add ionic strength adjuster at 2% of the standard solution volume. Ensure accurate preparation and contamination-free standard solutions. An electromagnetic stirrer is recommended during calibration. Perform calibration from the lower concentration to the higher concentration. Wait approximately one minute for potential stabilization after switching to each standard solution before confirming and proceeding to the next calibration point.
After calibration completion, verify the potential difference between the two points:
Monovalent ion electrodes (e.g., fluoride, chloride electrodes): acceptable slope range = 56 ± 4
Divalent ion electrodes (e.g., calcium electrode): acceptable slope range = 27 ± 4
Recalibrate if the slope falls outside the qualified range.

IV. Special Exception Handling
Calibration failure after prolonged electrode use may be caused by grease in water samples reducing electrode sensitivity.
Limescale in water samples may block the electrode sensing membrane and slow electrode response.
Testing strongly acidic or strongly alkaline water samples severely degrades electrode service life and drastically impairs sensitivity.
Electrodes used for more than six months commonly fail calibration due to natural aging.
Avoid measuring the three types of problematic water samples mentioned above. Thoroughly clean the electrode immediately after measurement. Replace the electrode if repeated calibration attempts remain unsuccessful.

V. Routine Maintenance & Calibration Interval
Short-term storage (within one week or frequent daily use): Soak the electrode in standard solution of the target ion at 10–20 mg/L to prevent internal crystal formation.
Long-term storage (more than one week): Use a pipette to drain all internal filling electrolyte, rinse the electrode thoroughly with deionized water, and store the electrode tip dry inside its protective cap.
Calibration cycle: Perform calibration at least once weekly to prevent measurement data drift.