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4.4.3 pH isothermal measurement principle
According to the pH isothermal measurement principle, the closer the test sample’s temperature is to the calibration
solution’s, the higher the accuracy of the measurement. So this principle is recommended to follow when conducting
tests.
4.4.4 Restore to factory default
The instrument has a function to return to factory default setting, which can be set up in P1.5 (refer to section 7.3).
Returning to factory default setting is to restore the meter to theoretical value (zero potential pH is 7.00, slope is
100%), and set all the parameters to default settings (see appendix 1). When the meter’s calibration or measurement
is performing abnormally, users can use this function to let the meter return to factory default mode, and then conduct
calibration and test again. Please note that this function is irreversible once used.
Maintenance of the pH Electrode
4.5.1. Daily maintenance
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 or pure water before taking a measurement.
Insert the electrode and tighten the capsule after measurements to prevent the solution from leaking. If the soaking
solution is turbid or moldy, replace the KCL solution. (Preparation: 26g KCL dissolved in 100ml pure water).
The electrode should not be soaked in pure or distilled water, protein solution or acid fluoride solution for long periods
of time. In addition, do not soak the electrode in organic lipids.
4.5.2. Calibration buffer solution
For calibration accuracy, the pH of the standard buffer solution must be reliable. The buffer solution should be
refreshed often, especially after heavy use. We recommend 10-15 times of use before replacing the pH buffers.
4.5.3 Protect glass bulb
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 pure water and dried. If a sample sticks to the electrode or it’s contaminated, the
electrode should be thoroughly cleaned using a soft brush and then rinsed with pure water. After that, soak it in the
KCL solution again for 6 hours.
4.5.4 Renew glass bulb
Electrodes that have been used over a long period of time will become aged. Submerge the electrode in 0.1mol/L
hydrochloric acid for 24 hours, then wash the electrode in pure water, then submerge it in KCL soaking solution for
24 hours.
The method to prepare 0.1mol/L hydrochloric acid: dilute 9mL hydrochloric acid in pure water to 1000mL.
For serious passivation, submerge the bulb in 4% HF (hydrofluoric acid) for 3-5 seconds, and wash it in
pure water, then submerge it in the soaking solution for 24 hours to renew it.
4.5.5. Clean contaminated glass bulb and junction (please refer to Table-8)
