Determination of chlorine dioxide in potable waters using chlorophenol red

Abstract

The determination of chlorine dioxide using chlorophenol red was investigated in the presence of various chlorinated species that can occur under normal water treatment conditions. Previously published methods employing chlorophenol red were found to be subject to unreported and significant interference from free chlorine (hypochlorous acid).

Glycine, ammonium sulphate and sodium cyclamate were investigated as possible reagents to suppress this interference. Glycine was found to be an unsuitable reagent owing to the direct reaction with chlorine dioxide. Sodium cyclamate yielded the best performance. When combined with the addition of thioacetamide after chlorophenol red, free chlorine concentrations up to 20 mg l^–1 could be tolerated without interference.

The finalised procedure employing sodium cyclamate and thioacetamide is simple, selective for chlorine dioxide in the presence of other chlorinated species and has a range suitable for the determination of the low concentrations of chlorine dioxide employed in potable water treatment.