SOLID-PHASE EXTRACTION AND SPECTROPHOTOMETRIC DETERMINATION OF CHLORINE IN AIR AND RESIDUALS OF FREE AND COMBINED CHLORINE IN WATER UTILIZING AZO-DYE FORMATION

Oxidation of phenylhydrazine-4-sulfonic acid to the 3-diazobenzenesulf onic acid cation and its electrophilic coupling with N-(1-naphthyl)eth ylenediamine dihydrochloride to give an azo dye is a new reaction sche me that is proposed for the spectrophotometric determination (545 nm) of chlorine in air and free and combined chlorine residuals in environ mental waters. Masking of foe chlorine with acetone permitted the dete rmination of combined chlorine residuals in water. The maximum molar a bsorptivity was found to be 1.46 x 10(6) l mol(-1) cm(-1). A rectiline ar calibration graph was obtained for 2.5-100 mu g l(-1) Cl. The azo d ye could also be preconcentrated by solid-phase extraction on a C-18 s orbent, leading to an enrichment factor of at least 40-fold. The limit of detection (without enrichment) was 0.2 mu g l(-1) Cl. Up to 50 mu g l(-1) bromate, 10 mg l(-1) chlorate, 40 mu g l(-1) copper(II) and 10 0 mu g l(-1) iron(III) did not interfere. Chlorine dioxide was removed by bubbling the water sample with nitrogen. A comparison of the propo sed method with the standard 4-N,N-diethylaminoaniline procedure was m ade and advantages of the present method are noted.