Chloride sensors have found wide application in the fields of environment monitoring, tideland agriculture, soil science and water supply systems since chloride is widely distributed in the form of compound in nature. Although high chloride concentrations in environmental samples do not cause harm to the human body, they can cause severe corrosion in metallic pipes, leading to the destruction of water systems and to the increase in the concentration level of metal ions in drinking water. Therefore, the maximum allowable Cl− level of 250mg·L−1 has been established by the World Health Organization (WHO) for drinking water and natural water.
Usually, chloride ions in solution can be measured by gravimetry, titrimetry, spectrophotometry, potentiometry, coulometry and ion chromatography. Among them, the major applications in the industrial field are spectrophotometry, potentiometry (ISE), and coulometry.
For this purpose, optical, fluorescent, and electrochemical sensors have been developed. Optical sensors enable measurement regardless of the pH or temperature of the solution, and fluorescent sensors have the advantages of good selectivity and high sensitivity to Cl- and short response time. However, these sensors are relatively expensive and have shortcomings of short lifetime due to photolysis or bleaching of the sensing materials.
In many cases, electrochemical sensors use potentiometry based on the half-cell potential of a silver/silver chloride (Ag/AgCl) electrode measured compared to a reference electrode at equilibrium. The potentiometric determination of chloride by Ag/AgCl electrode has been widely used in harsh applications due to its low cost, simple fabrication and long-term stability.
Kim Kyong Il, a researcher at the Faculty of Electronics, has proposed a new and simple fabrication method of a highly sensitive Ag/AgCl chloride sensor for real-time measurement of water quality. He fabricated the working electrode by electrodeposition and melt deposition of AgCl + Ag2S on the surface of Ag wire and coating the PVC film on it.
The study showed a good linear relationship between the logarithm of chloride ion concentration and the electrode potential when the chloride ion concentration in tap water, seawater and agricultural irrigation water ranged from 5×10-4 to 1mol·L-1. The potential response was affected by pH, but the ions commonly present in environmental samples such as K+, Ca2+, Na+, NO3-, SO4- were not affected.
For more details, please refer to his paper “A Simple Fabrication Method of Chloride Sensor Based on Hot-Dipped Ag/AgCl@PVC for Water Quality Monitoring” in “Water Air Soil Pollut” (SCI).
© 2021 KumChaek University of Technology