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- Winkler titration
- Air-saturated water
- Water-saturated air
Cleaning and Maintenance
[need to be paraphrased]
The component of the sensor that is sensitive to contamination is the membrane. Contamination results in lower readings when measuring or lesser slopes when calibrating because a portion of the membrane surface is not available for the diffusion of oxygen. The attempt to compensate for the contamination by adjusting the instrument does not agree with the water principle. It is preferable to clean the membrane. Acetic or citric acid with a concentration of 5--10% (percent in weight!) is used for calcium and iron oxide deposits and warm (<50C) household detergent is used for fats and oils.
Avoid strong mechanical treatment of the membrane during all cleaning activities because its thickness is on the order of m and it is easily destroyed. It is best to use a soft paper towel. Dissolved oxygen not clean the sensor in an ultrasound bath as this may cause the coating of the anodes to peel off.
Regeneration of the sensor becomes necessary when the function responds or when the slope (S) < 0.6 has decreased markedly when calibrating.
Basically, regeneration is required when the electrolyte solution is depleted, when the gold cathode has become coated with lead or silver, when the reference electrode is to xified or when the membrane is damaged or contaminated.
It consists of exchanging the electrolyte solution, cleaning the electrodes and exchanging the membrane head.
It is important to follow the operating manual exactly! Mistakes are then easily avoided.
The following points should be emphasized:
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!
Please note: The spacing lattice is clearly visible when the membrane head is held up against the light.
The result of an oxygen measurement can be documented in several ways:
Display of the concentration: The instrument requires the appropriate data of the calibration curve and uses them to calculate the concentration in mg/L (ppm is identical in this case), allowing for the temperature dependency of the individual parameters
Display of the percentage of oxygen saturation: The instrument measures the sensor current and calculates the partial pressure of oxygen according to the calibration. The current air pressure is measured for the calculation of the saturation partial pressure. The display corresponds to the quotient, converted into a percentage.
References
Erlich Industrial Development. D. O. theory. http://www.eidusa.com/Theory_DO.htm
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