Selective chlorine determination by gas diffusion in a tandem flow assembly and spectrophotometric detection with o-dianisidine

A fast, selective, sensitive and automated method for determination of free chlorine in industrial formulations and water samples is proposed. The automation of the flow assembly is based on the "tandem flow" approach, which uses a set of solenoid valves acting as independent switches. The operating cycle for obtaining a typical analytical transient signal can easily be programmed by means of friendly software running in the Windows environment. The manifold is provided with a gas diffusion unit which permits the removal of interfering species as well as concentrating the chlorine. The determination of chlorine is performed on the basis of the oxidation of o-dianisidine as the colorimetric reagent to a colored product that can be monitored at 445nm. The method (for a concentration time of 30s) is linear over the range 0.05-1.30µgml-1 chlorine; the 3sigma limit of detection is 0.05µgml-1; the reproducibility (as the R.S.D. of 42 peak heights for a 0.72µgml-1 chlorine solution) is 1.5% and the sample throughput is 38h-1.