DEVELOPMENT OF MINIATURIZED ANALYTICAL SYSTEM FOR RESIDUAL CHLORINE WITH ELECTROCHEMICAL SENSORS

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Chlorine in aqueous solutions is used for a number of purposes, such as disinfection and bleaching, and also as a powerful oxidizing agent in various manufacturing processes. It is known that chlorine is highly toxic, and additionally it can further react with other substances, such as phenols, in environment to produce chlorophenols, which are suspected to be carcinogens. Thus, the development of the new methods and devices for the reliable and continuous measurement of residual chlorine at trace levels had been conducted in the present work.Residual chlorine in water is generally present in the fibrin of hypochlorous acid (HOCl), or its conjugated base, the hypochlorite ion (ClO-). It was confirmed in this study that gold electrode exhibited very large reductive currents as well as good stability compared with platinum and glassy carbon electrodes in the pH range of 4-8. Based on the electrochemical sensors with gold electrode, the present study developed a portable miniaturized FIA … More system for on-site monitoring of residual chlorine in environmental samples. As for the purpose of on-site determination, miniaturization of the potentiostat along with a reduction in the complexity of the chip, low power consumption and a high dynamic range was developed in the current work. The potentiostat was built using an embedded controller microprocessor, an A/D converter a D/A converter, and operational amplifiers. It is available operated by a battery for a video camcorder (Sony NP-F550, 7.2 V 1500 mA/H). The size of the potentiostat is 150×100×40 mm and weight is only 350 g. The electrochemical measurements were controlled by a notebook computer and a laboratory-written software package via an RS-232C interface. It was confirmed that the amperometric response increased in proportion to the chlorine concentration up to 5μg/ml, and the detection limit for chlorine was 0.05 μg/ml. Besides a drastic reduction the size of the analytical system, such miniaturization achieved the advantages of increased speed, minimal mobile-phase consumption, and high sensitivity. The proposed method was successfully applied to the determination of residual chlorine in samples of pool water and tap water. The results were well agreed with those obtained by the N,N-diethyl-p-phenylenediamine (DPD) photometric method.The electrochemical behavior of trace chlorine was also studied in the presence of DPD at glassy carbon electrode by square wave voltammetry. In the lower pH value, a new reduction wave (+0.4 V vs Ag/AgCl) was observed, which is closely followed by the reduction of DPD (+0.5 V vs Ag/AgCl). The new peak at ca. +0.4 V was suggested to be generated by chlorinated product of DPD which is in proportion to the concentration of chlorine. But this peak was seriously overlapped by the background of DPD when the concentration of chlorine is low. In this study, signals-ratio method combined with wavelet transform was proposed for the resolution of a weak voltanunteric signal overlapped by other coexisted components. With the proposed method, the overlapped voltammetric peaks can be well separated and thereby the chlorine at trace level could be determined in a linear range of 0 to 100 μM with a detection limit of 0.5 μM. The advantages of proposed method are sensitive and free of some oxidant interthrences which could be a problem in DPD colorimetric method. The mechanism and the application in determination of real samples are now in progress. Less