Development of detector for the flow analysis of residual chlorine using a platinum oxide sheet electrode

A residual chlorine detector for flow analysis was developed with a platinum oxide sheet electrode. The detector consists of a working electrode (platinum oxide sheet), a counter electrode (platinum wire) and a reference electrode {saturated calomel electrode (SCE) }. A sample solution containing residual chlorine (sodium hypochlorite and monochloramine) was pumped at a flow rate of 0.7 ml min(-1) and mixed with a buffer solution (pH 9.8, sodium carbonate) containing potassium iodide. The residual chlorine reacted with potassium iodide, producing iodine in a mixing coil. After the mixed solution was led into the detector, the produced iodine was reduced with the working electrode at + 0.125 V vs. SCE. The response time was about 6 min. A linear relationship between the concentration of residual chlorine and reducing current (response) was obtained in the concentration range of 0.04 to 2.6 mgCl(2) l(-1). The relative standard deviation was about 2.5%(n = 8) for 1-0 mgCl(2) l(-1). The lifetime of the detector was about several hundred times of experiments. A monochloramine was the reaction product of sodium hypochlorite with ammonium chloride. When the potassium iodide was not added to the buffer solution, the reducing current was restricted to the concentration of the sodium hypochlorite. The concentration of monochloramine was equivalent to the difference between two responses.