Thermo Fisher Scientific ECFP21A1A1 Differential pH Sensor - Manual (Page 13)

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pH SENSOR MAINTENANCE
4.1 Cleaning the pH Sensor Head
4.1.1 In order to maintain an accurate measurement value, the sensor will need occasional
maintenance. The maintenance interval will be dictated by the process in which it is
installed. The harsher the process, the more often the sensor will require maintenance.
Regular maintenance will yield a longer sensor life.
4.1.2 The sensor cleaning procedure is as follows:
4.1.2.1 Remove sensor from service and rinse or spray it with warm water to remove heavy
deposits.
4.1.2.2 Soak the sensor in a container of hot detergent water for one hour. Do not use
detergents that contain oily skin softeners like aloe or lanolin that can coat the glass
electrode. Alconox® and Dawn™ dishwashing liquid work well.
4.1.2.3 Use a soft-bristled brush, such as a soft toothbrush, and hot detergent water to scrub
the entire electrode end of the sensor, being careful not to scratch or break the glass
electrode.
4.1.2.4 Rinse the electrode end with clean warm water.
4.1.2.5 If deposits are still present on glass electrode repeat steps 2 and 3. In the case of
lime or other mineral deposits a weak solution (about 0.1 M) of hydrochloric acid
may be used. In some cases, a dilute solution (about 10:1) of water and chlorine
bleach or a solution of water and EDTA may also work. Stubborn oil or grease
deposits may require cleaning with a solvent such as acetone or alcohol. Protein
deposits may be cleaned with a pepsin-based cleaning solution. Bacterial or mold
growth may be removed with dilute chlorine bleach.
Caution: Ensure that dangerous chemical reactions will not occur between process
deposits and cleaning solutions. Compounds of cyanide and hydrochloric acid will react
and pose health risks. Cyanide is often used in electroplating and in gold refining. If in
doubt about potential chemical reactions, check with a chemist before cleaning.
4.1.3 Before returning the sensor to service, allow it to soak in water or buffer at ambient
temperature for about an hour to restabilize the pH electrode and the salt bridge.
4.1.4
After cleaning the sensor, calibrate sensor per instructions in the Alpha pH2000D
controller manual.
4.1.5
Reinstall sensor in process.
4.2 pH Sensor Refurbishment – Replacing the Salt Bridge and Reference Solution
4.2.1
If the sensor head has been cleaned (see section 4.1.2) and calibration cannot be achieved,
replace the salt bridge and reference solution.
4.2.2
Hold the sensor firmly with the electrode tip facing upwards. Remove the existing salt
bridge by using a 15/16 wrench (24mm) and turning it counterclockwise. Dispose of the
salt bridge using an approved method.
4.2.3
Pour out the old reference solution. Rinse the reservoir with distilled or de-ionized water.