Fiber-optic detection of chlorine in water

Monitoring of the chlorine content represents important issue of the control of water quality. Crucial points of this control are detection of low chlorine concentrations around 1 ppm and reversibility of chemical reactions between strong oxidation agent, chlorine and opto-chemical transducers used for the detection. This paper deals with fiber-optic detection of chlorine in water by using a commercially available absorption transducer o-phenylenediamine (o-PDA) electrochemically immobilized onto fiber-optic substrates coated with Indium–Tin-Oxide (ITO).Sensitive layers of the absorption transducer o-PDA were prepared electrochemically by cyclic voltammetry. The layers were applied onto declad segments of polymer-clad silica fibers coated with a thin conductive ITO layer making the electrochemical deposition possible. Prepared detection elements were exposed to aqueous solutions of chlorine of various concentrations and spectral response and time response curves were measured. Oxidized sensitive layers were regenerated chemically by using a solution of sodium thiosulfate. A limit of detection of chlorine in water of about 0.14 ppm has been achieved, making the detection of chlorine in water within the hygienic limits feasible.