Solid-phase extraction and spectrophotometric determination of chlorine in air and residuals of free and combined chlorine in water utilizing azo dye formation

Abstract

Oxidation of phenylhydrazine-4-sulfonic acid to the 4-diazobenzenesulfonic acid cation and its electrophilic coupling with N-(1-naphthyl)ethylenediamine dihydrochloride to give an azo dye is a new reaction scheme that is proposed for the spectrophotometric determination (545 nm) of chlorine in air and free and combined chlorine residuals in environmental waters. Masking of free chlorine with acetone permitted the determination of combined chlorine residuals in water. The maximum molar absorptivity was found to be 1.46 × 106 l mol–1 cm–1. A rectilinear calibration graph was obtained for 2.5–100 µg l–1 Cl. The azo dye could also be preconcentrated by solid-phase extraction on a C18 sorbent, leading to an enrichment factor of at least 40-fold. The limit of detection (without enrichment) was 0.2 µg l–1 Cl. Up to 50 µg l–1 bromate, 10 mg l–1 chlorate, 40 µg l–1 copper(II) and 100 µg l–1 iron(III) did not interfere. Chlorine dioxide was removed by bubbling the water sample with nitrogen. A comparison of the proposed method with the standard 4-N,N-diethylaminoaniline procedure was made and advantages of the present method are noted.