5. Maintenance (calibration and replacement)
Cleaning Instructions
The solution used to clean pH/ORP electrodes
depends on the presence of possible contaminants.
pH/ORP electrodes may show slow response due
to sensor coatings or reference clogging. Use the
guide below to choose the appropriate cleaning
solution options:
•
For general cleaning: Soak the pH/ORP electrode
in 0.1 M HCl or 0.1 M HNO3 for 20 minutes.
Alternatively, an ORP electrode’s platinum or
gold sensor plate or band can be swabbed
with an isopropyl or ethyl alcohol if convenient.
Rinse well in deionized or tap water before use.
• For removal of protein deposits: Soak the pH
electrode in a solution containing 1 % pepsin
and 0.1M HCl for 15 minutes to 1 hour depending
on how dirty it may be. Rinse well in deionized
or tap water before use. (NOTE Pepsin is readily
available as a powder from a lab supply house).
• If it is likely that the electrode was stored dry for
an extended period and the reference junction
may be dried or have the crystal formation
in the pores, soaking the electrode in warm
soaking/storage solution (~50 °C) may accelerate
the reconditioning of the reference junction.
After any of the cleaning procedures, it is good
practice to thoroughly rinse the electrode with
deionized water, recondition, and recalibrate the
electrode.
Troubleshooting minor issues
Improper conditioning may involve the glass
pH sensor not being properly “hydrated”, or
the reference junction not fully prepared for ion
- sharing. For example, the pores of the reference
junction may have dried potassium chloride crystals
that need to be wetted to “recharge” the salt bridge
function of the reference junction. Signs of improper
conditioning may be:
1) Inaccuracy of a pH electrode soon after calibration
2) Unstable, erratic, or extremely drifty readings
3)
Lack of signal, or over- range situation
if the reference junction is not working at all
(meter dependent)
If it is likely that the electrode was stored dry for
an extended period and the reference junction may
be dried or have the crystal formation described
above in the pores, soaking the electrode in warm
soaking/storage solution (~50 °C) may accelerate
the reconditioning of the reference junction.
However, prolonged drying conditions could
severely damage the glass pH sensor. After
conditioning the electrode, rinse with deionized
water. The electrode is ready for calibration
and measurement.
Calibration
pH Electrodes
Since glass pH electrodes measure the H+ (hydrogen
ion) concentration (or activity) relative to their
reference half- cells, they must be calibrated once
during its lifetime (after two years of use) to ensure
accurate, repeatable measurements. It is important
to use reliable pH Buffers to calibrate your pH
electrode For more information follow the steps
present in the Gecko app.
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