Potentiometric Free Chlorine Detection without Using Conventional Reference Electrodes

Chlorine disinfection of water is one treatment method to supply safe tap water. The quantitative monitoring of free chlorine concentration as an important water quality index is effective to maintain tap water hygienic safety. In this study, a simple potentiometric sensor which is composed of two dissimilar metal electrodes (a pair of platinum and austenitic stainless steel: SUS316) was evaluated in synthetic and actual tap water. It was demonstrated that the open circuit potential of each electrode had a different sensitivity to free chlorine and that the difference could be extracted as the sensing signal without using conventional reference electrodes. In a flowing system using tap water, more than 300 mV of large sensor signal and good reproducibility were observed at a free chlorine concentration of 0.6 mg l −1 . The long-term baseline drift was within the range of ±10 mV and the sensor was almost immune to various environmental factors such as temperature, pressure, flow rate, and conductivity, but not for pH. These results would pave the way to develop various sensor applications that could be directly applied to tap water pipelines for continuous in-line monitoring of residual chlorine with low cost and maintenance.