Model PH220 Version 3.1 11/2005
8
Electrode Maintenance and Troubleshooting
Most pH measurement difficulties are caused by the electrode. Careful handling and proper
storage of the electrode will increase measurement accuracy and electrode life.
Electrodes should be rinsed to remove all traces of storage solution, process medium, or
previous test solution.
Electrode Storage
The electrode should be stored in a soaker bottle or wetting cap filled with pH4 buffer.
Never store an electrode in distilled or deionized water as this will cause migration of the fill
solution from the electrode.
Electrode Cleaning
The type of electrode coating that occurs over time will determine the cleaning method.
Soft coatings can be removed by vigorous stirring or by using a squirt bottle. Organic
chemical coating (hard coatings) should be chemically removed. Only in extreme cases
should the bulb be cleaned mechanically.
Troubleshooting an Electrode
Symptom
Cause
Recommendation
Clogged Junction
Soak in 4.07 M Potassium Chloride (KCl)
@ 60
o
C for 30 minutes.
Strong Alkaline measurement
Soak in 0.1 M HCL overnight.
Deteriorated Gel layer
Replace electrode.
Protein coating on electrode
surface
Soak in 1 gm Pepsin dissolved in 100ml of
0.1 m HCL for 30 minutes or as needed.
Oil, paint, dyes, suspended
solids etc. are on sensor
Rinse electrode alternately with a materials
solvent and a buffer 7.00.
Organic solvents are coating
the sensor
Organic mole fraction has to be less than
50% to assure reasonable readings. Limit
time of measurement. Keep probe in the
7.0 buffer between readings.
Long response time or
reading drift
Dehydrated membrane
Read solution for dry bulb below:
Dry Bulb
Long term storage without
wetting
Soak electrode tip in wetting cap filled with
1ml 7.00 buffer for 24 to 48 hours
Static Charge
Wiping electrodes
Rinse electrode in 7.0 buffer and blot. Do
no wipe electrode.
Same readings in different
buffers and samples
Cracked or broken bulb
Replace electrode. Use bulb guard. Avoid
plunging electrode to bottom of container
and spinning bars. Wetting cap will protect
bulb between tests.
Erratic LCD display
Samples have low ionic
strength (lacks salt); e.g.
distilled, de-ionized, boiled,
lake water (high pressure)
For each 50 ml of sample add 1 drop
(50uL) of SAT. KCl (No alteration in pH will
occur using inert KCl).
