Thermo Fisher Scientific EC620130 Series Combination pH Electrodes - Manual (Page 4)

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5) To eliminate temperature errors associated with the electrode, manual or automatic temperature
compensation (ATC) should be used for best accuracy. Since pH changes with temperature, the sample
temperature should always be noted with pH readings, for example, “pH 8.43 @ 23.2 °C”.
CALIBRATION/STANDARDIZATION
New EC620130 series pH electrodes are factory-tested to have an efficiency or “slope” of > 95%. The
theoretical pH response is 100% (59.16 mV/pH unit) and therefore the millivolt difference between pH
4.00 and pH 7.00 certified calibration standards at 25ºC should be 177.48 mV. A 95% slope means that a
new accumet electrode will have a response of at least 168.61 mV between these values. As electrodes
naturally age, this efficiency deteriorates. Periodic calibration against known standards is necessary to
ensure the electrode’s efficiency. Most pH meters have features to display the current electrode slope,
protection that warn users of a low slope (usually 90%) and/or features that prevents erroneous
calibrations.
After completing calibration with the meter, the measured pH reading of each calibration buffer can be
compared to the pH value indicated for each buffer at the actual temperature. A chart with pH at various
temperatures is usually found on the calibration standard packaging or label. Using one-point
standardization, proper response is indicated if the reading is within ± 0.05 pH units from the
standardization point within 30 seconds when using certified pH buffers . Multiple-point standardization
is recommended for more precise measurements. To provide a linear response in the area of interest, use
two calibration standards that bracket the expected sample pH.
STORAGE
Storing electrodes in distilled or deionized water is NOT recommended as it will deplete the hydration
layer of refillable electrodes, and decrease the life of non-refillable electrodes. The electrode storage
bottle containing storage solution can be used for short or long term storage. For refillable electrodes,
the electrolyte level in the outer cavity should be kept above the level of the solution being measured.
Ensure that the fill hole is closed when not in use.
TROUBLESHOOTING
SYMPTOM / CAUSE (REMEDY)
• No response, all buffers or samples read the same pH—usually pH 7.00 or 0 mV / Broken
sensing bulb or wiring problem (replace electrode), probe not connected to input (verify correct
channel selection when using multiple-channel meters), probe is not in contact with sample
(remove electrode storage bottle or rubber bulb guard), meter automatically has frozen reading
(verify that the ‘Hold’ feature or ‘Auto Read’ feature is set to ‘Off’ when using meters with this
feature).
• Slow response with excessive crystallization inside probe / electrolyte flow clogged from
supersaturated electrolyte (“flush & fill” by remove the filling solution through the fill hole with a
syringe or by shaking it upside down. Repeatedly flush and rinse the reference cavity with clean,
60-80°C water to dissolve crystals until removed. Replace filling solution and re-hydrate
electrode in storage solution or pH 4 buffer, (ensure fill hole is in open position). To prevent this
in the future, ensure that the fill hole is closed when electrode is not in use.
• Dried salt deposits present / electrolyte residue deposited on electrode surface –often with
new electrodes or periods of non-use. Simply dissolve the deposits in warm tap water followed
by a brief soak in pH 4 buffer.
• Slow Response, Noisy, unstable, or erratic readings / sensing bulb dry or dirty (clean
electrode with mild detergent & warm water and re-hydrate electrode) , temperature may be
changing rapidly or electrode may be thermally shocked (allow electrode to reach sample
temperature), sample may be non-aqueous (take 30 second readings and soak in pH buffer for
one minute between measurements)