Dissolved oxygen meters are extensively used in various fields, such as wastewater treatment, aquaculture, and in the pharmaceutical industry, to monitor and control the oxygen concentration levels. These meters play a crucial role in maintaining the optimum oxygen concentration required for the survival and growth of living organisms.
Two of the commonly used electrodes in dissolved oxygen meters are polarographic and Clark-type electrodes. Both these electrodes are effective in measuring the dissolved oxygen concentration in a water sample, but they differ in their working principle, reliability, accuracy, and sensitivity.
In this article, we will discuss the differences between these two electrodes.
1. Working principle:
The polarographic electrode works on the principle of electrochemical reduction where an electric potential is applied to the electrode, and the dissolved oxygen in the sample diffuses through the electrode membrane. The oxygen is electrochemically reduced to produce a current, which is proportional to the dissolved oxygen concentration.
The Clark-type electrode, on the other hand, works on the principle of oxygen-permeable membranes. The electrode comprises a platinum cathode and a silver anode, and both of them are suspended in an electrolyte solution. Oxygen from the sample diffuses through the permeable membrane and reacts with the cathode, producing a current that is proportional to the dissolved oxygen concentration.
2. Reliability:
Polarographic electrodes are more reliable than Clark-type electrodes because they are less prone to fouling and clogging. The polarographic electrode membrane is usually made of Teflon, which is unreactive and resistant to fouling, whereas the Clark-type electrode membrane is made of a cellulose acetate or other fibrous materials that are prone to clogging or fouling.
3. Accuracy:
Both polarographic and Clark-type electrodes are accurate in measuring dissolved oxygen concentrations. However, the polarographic electrode is more accurate as it is less affected by changes in temperature, pressure, salinity, and other factors that can affect the oxygen measurements.
4. Sensitivity:
The polarographic electrode is more sensitive than the Clark-type electrode. It can detect dissolved oxygen concentrations as low as 0.01 ppm, whereas the Clark-type electrode can detect dissolved oxygen concentrations as low as 0.1 ppm.
5. Maintenance:
The maintenance of the polarographic electrode is simple, as it does not require any replacement or cleaning. However, the Clark-type electrode requires regular cleaning and replacement of the electrolyte solution and membrane.
Conclusion:
Both polarographic and Clark-type electrodes are commonly used in dissolved oxygen meters. However, the choice of electrode depends on the application and the user's requirements. If accuracy and sensitivity are the main factors, then the polarographic electrode is preferred. If reliability and maintenance are the main factors, then the Clark-type electrode is preferred.
In conclusion, the choice of electrode should be based on the user's requirements, and it is crucial to choose the right electrode for accurate and reliable dissolved oxygen measurements.
