Differential UV–vis absorbance can characterize the reaction of organic matter with ClO2

Abstract UV–vis differential spectroscopy was applied to characterize and quantify the spectral changes after ClO 2 oxidation of ten humic substances, seven aromatic model compounds and four surface waters. The differential spectra of ten humic substances after ClO 2 oxidation all exhibited a peak near 230 nm and a broad absorbance band with a maximum at around 316 nm. The differential spectra after ClO 2 oxidation were distinguished from the one after chlorination, which was indicative of their different oxidation mechanisms. The differential spectra after ClO 2 treatment were well fitted by seven Gaussian bands with maxima at about 200, 225, 240, 276, 316, 385 and 457 nm. Differential absorbance at 316 nm and 400 nm (denoted as DA 316 and DA 400 , respectively) were found to best quantify the degradation of organic matters during ClO 2 oxidation with negligible interferences from water matrixes. Oxidation of substituted functional groups on aromatic structures, rather than destruction of aromatic rings, was more responsible for chlorite formation. Spectral parameters–DA 316 and DA 400 showed strong correlations with ClO 2 consumption and chlorite formation during ClO 2 oxidation of humic substances and surface water samples. The results demonstrate that DA 316 and DA 400 can serve as promising indicators of chlorite formation and ClO 2 consumption, which provide a practical approach for online water quality monitoring during ClO 2 water purification.