Colour reaction of free chlorine with p-amino- N,N-diethylaniline in the presence of alcohol and its analytical application

Abstract

A simple, precise, rapid-colour-forming and stable spectrometric method has been developed for determining free chlorine in water. p-Amino- N,N-diethylaniline reacts with free chlorine almost instantaneously in the presence of alcohol to form a red oxidized product with absorption maximum at 513 nm. Beer's law is obeyed in the free chlorine concentration range of 0–2 μg ml −1. The molar absorptivity is 1.79 × 10 4 l mol −1 cm −1, limit of detection 0.0036 μg ml −1, relative standard deviation 1.51%, and amount of free chlorine 7 μg. The colour reaction rate and absorbance are independent of temperature in the range 3–45 °C and the stable absorptivity lasts for at least 1 h. The method is satisfactory for the determination of free chlorine in aqueous solution.