AbstractA novel electrochemical sensor with a polytetrafluoroethylene (PTFE) membrane (10 voids) and a porous carbon felt electrode has been fabricated for the determination of residual ozone in water. The carbon felt has a large specific surface area which can capture all of the ozone transferred from the sample solution through a PTFE membrane, and an extremely low concentration of ozone (about 0.5 ppb) can be detected. The relationship between the current response and the ozone concentration obtained by the Indigo method was linear over the range 5–800 ppb. The sensitivity was calculated to be approximately 10 μA/(ppm cm2) at 12°C. The relative standard deviations (RSDs) of the response currents were below 5 when the ozone concentration was higher than 50 ppb. The response to 1 ppm residual chlorine is about 1.3 of that of the same concentration of ozone in solution at pH 5. The measured current was reproducible over three months and was found to be suitable for use as an on‐line s
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