Rhodamine 6G chemiluminescence for the determination of free chlorine in tap water by a flow-injection method

Abstract

A chemiluminescence system is described for the specific determination of free chlorine by a reversed flow-injection method. The light emitted from the reaction between Rhodamine 6G and free chlorine (HOCl) under unbuffered conditions allows free chlorine in tap water to be determined with no interference from combined chlorine (chloramines). The limit of determination (signal to noise ratio = 3) is 1 × 10^–7 M, the linear range is two orders of magnitude, the sampling rate is 240 samples h^–1 and the relative standard deviation (n= 10) is 2.0% for 1 × 10^–5 M free chlorine. Common inorganic species give rise to no light emison. Among oxo acids of chlorine, only chlorite ion slightly elicits light, 1 × 10^–3 M ClO₂ ^– providing a signal 3% of that for 1 × 10^–5 M HOCl. Inorganic species and chloramines co-existing in tap water do not interfere.