Photolytic spectroscopic quantification of residual chlorine in potable waters

Quantitative detection of aqueous, chlorine-based disinfectants (HOCl and OCl–) in potable waters is demonstrated using UV spectroscopy combined with in situ photolysis. The information on a target species is obtained through measurement of a ‘double signature’, namely spectra taken before and after the photolytic reaction. In the case of chlorine disinfectants the photolytic reaction is a simple destruction of the absorbing species. In a calibrated water we obtained measurement uncertainties of better than 0.027 ppm for both disinfectant species. The combination allows pH-independent, on-line, reagentless measurement of disinfectant strength at and above the 0.05–2.0 ppm concentrations typical in treatment plant and potable water distribution networks.