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As in the case for the polarographic electrodes, a voltage is applied externally while an internal potential is generated as in the galvanic electrodes.
Polarographic Electrode
A typical polarographic electrode consists of a silver anode, a gold or platinum cathode and an electrolyte solution (KCl or AgCl). In order to create a sensor, a constant voltage of 0.8 volts is applied to the probe, and a digital meter is installed to read the DO response measured by the sensor.
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Limitations
- Response time is described as the time required for the electrode to reach >90% of the output. Typical response time for polarographic sensors are is 30 sec, which makes them not compatible to be used for dynamic measurements.
- Warm-up time for this type is approximately 10 minutes. Wrong readings will occur if measurements are made when the required amount of time has not been attained.
- Chloride ions in the electrolyte will be eventually consumed resulting in gradual drift in the electrode signal. The electrolyte must be replaced.
- Since the electrode consumes oxygen, readings are affected by flow across the sensor tip. Thus enough flow rate at the membrane (or sample renewal rate) must be ensured for accurate results.
Galvanic Electrode
Group Members: Eila Myllylä, Chi-En Shan, Olga Gerasimenko, Judit Nyári & Nhat Nguyen
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