Photocatalytic degradation of the herbicide isoproturon: characterisation of by-products by liquid chromatography with electrospray ionisation tandem mass spectrometry

By-products arising from immobilised TiO2-catalysed photodegradation of the herbicide isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] in aqueous solution under solar radiation were analysed by reversed-phase liquid chromatography combined with electrospray ionisation ion trap mass spectrometry. Structural information on by-products, formed at different degradation times, was then obtained from interpretation of the relevant MS/MS spectra. Several species were identified through this approach, and in many cases several isomers were found. As expected, most byproducts resulted from single or multiple hydroxylation (by photo-generated OH. radicals) of the isoproturon molecule at different positions. However, substitution of some functional groups of the herbicide (isopropyl or methyl) by OH. was also observed. A possible degradation scheme is hypothesised