pH Measurement, Calibration, and Electrode Considerations
Error messages ERR-1: Electrode zero potential error and ERR-2: Electrode slope error; For
either error, check the following:
1. Air bubbles in the electrode bulb. Shake rigorously to remove air bubbles
2. Accuracy of the pH buffers used in calibration. Replace buffers if necessary
3. Set meter to its factory default state in Parameter P7 (previous section of manual)
Calibration intervals depend on the sample, the electrode performance, and the required
accuracy. For high accuracy measurements (≤±0.02pH), the meter should be calibrated
immediately before taking a measurement. For general accuracy (≥±0.1pH), the meter can be
calibrated and used for approximately one week before the next calibration.
The meter must be recalibrated in the following situations:
1. New probe, or probe that is unused for a long period of time
2. After measuring acids (pH<2) or alkaline solutions (pH>12)
3. After measuring a solution that contains fluoride or a concentrated organic solution
4. If the solution’s temperature differs widely from the calibration solution temperature
The soaking solution contained in the supplied protective bottle is used to maintain activation in
the glass bulb and junction. Loosen the capsule, remove the electrode and rinse in distilled
water before taking a measurement. Insert the electrode and tighten the capsule after
measurements to prevent the solution from leaking. If the soak solution is turbid or moldy,
replace the solution.
To prepare a soak solution: Use 25g pure KCL dissolved with purified water and diluted to
100mL. The electrode should not be soaked in a distilled water protein solution or an acid
fluoride solution for long periods of time. In addition, do not soak the electrode in organic silicon
lipids.
For calibration accuracy, the pH of the standard buffer solution must be reliable. The buffer
solution should be refreshed often, especially after heavy use.
For best accuracy, always keep the meter clean and dry, especially the meter’s electrode and
electrode jack. Clean with medical cotton and alcohol if necessary.
The sensitive glass bulb at the front of the combination electrode should not come in contact
with hard surfaces. Scratches or cracks on the electrode will cause inaccurate readings. Before
and after each measurement, the electrode should be washed with distilled water and dried. Do
not clean the glass bulb with a tissue for it will affect the stability of the electrode potential and
increase the response time. The electrode should be thoroughly cleaned if a sample sticks to
the electrode. Use a solvent if the solution does not appear clean after washing.
Electrodes that have been used over a long period of time, used in a strong solution that has
damaged the sensitive bulb, or used with a substance resulting in a jam at the junction will be
become passivated; the sensitivity will decrease, its response will slow, and the readings will be
inaccurate. Replace the electrode as soon as possible in these cases.
For abnormal readings, try calibrating again; if the problem persists replace the Electrode. The
user can also try resetting the meter to factory default conditions per Parameter P7 (detailed in
an earlier section). Electrode life can be shortened by heavy use, extreme conditions, and
improper maintenance.
