Spectrophotometric determination of free chlorine in air

Abstract

A spectrophotometric method that is suitable for the micro-determination of free chlorine in ambient air is described. When free chlorine is absorbed in an alkaline solution of 4-nitroaniline, an orange-brown colour develops, with a molar absorptivity (ε) of 19 000 at 485 nm. The method is suitable for the determination of chlorine in the range from a few parts per hundred million to about 20 p.p.m.

Ozone, ammonia and sulphur reducing gases interfere with the reaction, but these interferences can be reduced. Features of the method include high sensitivity, stability of the reagents and coloured reaction product, high collection efficiency, relative specificity to chlorine, reproducibility, simplicity and convenience.