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Troubleshooting
Follow a systematic procedure to isolate the problem. The pH
measuring system can be divided into four components: pH meter,
electrode, sample/application and technique.
pH Meter
The meter is the easiest component to eliminate as a possible cause of
error. Orion pH meters include an instrument checkout procedure and
shorting cap for convenience in troubleshooting. Refer to the pH meter
user guide for directions.
Electrode
To test electrode operation:
1. Connect the electrode to a working meter that has a mV measuring
mode. Set the meter to the mV mode.
2. Rinse the electrode with distilled water and then insert the
electrode into fresh pH 7 buffer. When the reading is stable, record
the mV value of the pH 7 buffer. The mV value should be in the
range of -30 to +30 mV.
3. Rinse the electrode with distilled water and then insert the
electrode into fresh pH 4 buffer. When the reading is stable, record
the mV value of the pH 4 buffer. The mV value should be in the
range of +150 to +210 mV.
4. Calculate the absolute mV difference between the two buffers. The
mV difference should be 160 to 180 mV. The actual mV values will
change as the electrode ages, but the mV difference between the
two buffers should always be 160 to 180 mV.
5. If the electrode fails this procedure, clean the electrode thoroughly
as directed in the Electrode Maintenance section and repeat the
procedure.
If the electrode response is slow or drifting and the electrode is
refillable, drain and refill the electrode with fresh ROSS fill solution, Cat.
No. 810007.
Replace the electrode if cleaning and maintenance fail to rejuvenate it.
Sample/Application
The electrode and meter may operate with buffers, but not with the
sample. In this case, check the sample composition for interferences,
incompatibilities or temperature effects. Refer to the Interferences
section.
Technique
If trouble persists, review operating procedures. Review the calibration
and measurement sections to be sure proper technique has been
followed.
Thermo Scientific
Thermo Scientific Orion
ROSS Ultra, ROSS Ultra Triode and ROSS pH Electrodes
|
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