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Regeneration of the sensor is required when the function responds has dropped remarkably when calibration. This is caused by the depletion of electrolyte solution when the membrane is damaged or contaminated. To maintain the sensor, exchanging the electrolyte solution and membrane head and cleaning the electrodes are needed.
In general, electrode maintenance should only be necessary about once per year for steady-state polarographic sensors and about once every 3 months for steady-state galvanic sensors. Do not perform the following maintenance procedures just because a sensor ‘looks’ dirty. Only perform the following procedures if the instrument will not calibrate or if the readings are unstable and a regular membrane change did not correct either of these problems. http://www.eidusa.com/Theory_DO.htm#Cleaning of sensors
The following points should be emphasized when carrying out the cleaning and maintenance process. Source: http://www.eidusa.com/Theory_DO.htm#Cleaning of sensors
- The sensor must be disconnected from the meter. When the sensor is connected and submersed in the cleaning solution, no chemical reaction takes place between the solution and the oxidized reference electrode surface; instead, the cleaning solution may become electrolyzed!
- Use the cleaning or electrolyte solution suitable for the particular sensor as stated in the operating manual! A solution that is suitable for silver electrodes cannot regenerate lead electrodes!
- Only the gold cathode should be polished; the counter electrode is merely wiped clean with a soft cloth to wipe away easily removable salt deposits! A spotty coating after regeneration of the lead or silver electrodes does not impair measurements!
- When polishing the gold electrode, only use the moistened EID abrasive film that has a special grain that polishes and do not scratch!
- It is also recommended to use a new membrane head since the used membrane cannot necessarily guarantee that the membrane fits correctly against the gold cathode which is ensured by a spacing lattice on the inside of the membrane. Baggy clothing don't fit either!
Note:
- The spacing lattice is clearly visible when the membrane head is held up against the light.
- Always re-calibrate an instrument after changing a membrane.
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