Determination of dissolved ozone in water by chemiluminescence method with Rhodamine B

Abstract

In order to determine dissolved ozone(O₃aq) in atmospheric water droplets or ozone-treated water, an aqueous phase chemiluminescence (CL) method using Rhodamine B was studied. Standard O₃aq samples were prepared by passing air containing ozone through purified water. Equilibrium between gas and aqueous phases was attained within 30 min and it was confirmed that Henry's law held even at very low concentrations. The continuous chemiluminescent analyzer consisted of metering pumps, a glass reaction cell (0.7 ml), a photomultiplier and a photon counter. Care was taken to minimize the decomposition of O₃aq in the sampling line. The optimum reagent composition for CL intensity was determined to be 60 mg l^-1 Rhodamine B and 10mg l^-1 gallic acid. Gallic acid was added so as to obtain a faster CL response. CL intensity was proportional to the O₃aq concentration at least up to 400 ng ml^-1 and the detection limit(S/N=3) was estimated as 0.03 ng ml^-1, which was much lower than the methods currently used. The overall reproducibility including the gas-liquid partition process for samples (O₃aq: 110ng ml^-1) was ca. 9% as a relative standard deviation. Halide ions, aldehydes and hydrogen peroxide interfered with the measurement.