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We report the benefit of using an optimized composite electrode, based on a multiwall carbon nanotubes and epoxy resin, as working electrode in an automated flow system. The optimal composite electrode composition consists in a 10% carbon nanotubes and 90% epoxy resin. This composition provides lower limit of detection and increases the stability and reproducibility of the analytical signal compared to the 20% conventional composition electrodes. Moreover, the standard solutions are on-line prepared with an automated flow system. The integration of the developed carbon nanotube electrodes in the proposed flow system provides a highly sensitive analyzer for free chlorine determination in water down to the 20microgL(-1). The working range was found to be 0.02-4mgL(-1) with an analysis time of 60s. The system sensitivity was maintained into the control limits (+/-2sigma) for one month, with a mean value of -0.146 (+/-0.008) microALmg(-1). Validation of the analytical system has been performed by the successful determination of free chlorine in tap water and swimming pools water samples.

Carbon dioxide is seldom used as pH reducer in swimming pools. Nevertheless it offers two interesting advantages. First, its use instead of the usual hydrochloric acid avoids the characteristic and serious accident of mixing the disinfectant with that strong acid, which forms a dangerous chlorine gas cloud and, second, it allows the facility to become slightly a depository of that greenhouse gas. This work introduces the experience of using CO(2) as pH reducer in real working swimming pools, showing three more advantages: lower chlorine consumption, lower presence of oxidants in the air above the swimming pool and a diminished formation of trihalomethanes in the swimming pool water. Experiments lasted 4years and they were run in three swimming pools in the Barcelona area, where the conventional system based upon HCl and a system based upon CO(2) were consecutively exchanged.

This work reports on the performance of a user-friendly flow injection analysis (FIA) system for the monitoring of free chlorine. A methacrylate flow cell integrating a gold thin-film microelectrode, together with an on-chip gold counter electrode, both fabricated by microfabrication technology, provided robustness, low output impedance, rapid response and low cost to the proposed flow system. An external Ag/AgCl reference electrode placed downstream the chip completes the electrochemical cell. Amperometric detection of chlorine was carried out at a set potential of +350 mV, without oxygen interference. The proposed flow system responded linearly to chlorine concentrations in a range from 0.2 to 5 mgl(-1), with a sensitivity of 0.23 microAlmg(-1), the estimated limit of detection being 0.02 mgl(-1). In addition, the system response was kept stable for at least 10 days (+/-3sigma criterion), by keeping the flow system in an inert atmosphere when not in use. Fifteen samples of swimming pool waters were analyzed and no matrix effects were detected. Also, results were in good agreement with those obtained by a standard method. The excellent analytical performance of the system together with its good working stability would also enable its application for the detection of chlorine in other matrices such as tap water or chlorine stock solutions.