Photolysis of clothianidin by Xenon lamp was investigated by Ultra-Performance Liquid Chromatography Electrospray Ionization tandem mass spectrometry (UPLC-ESI/MS/ MS). Quantitative study on the photodegradation of clothianidin found that the photodegradation obeyed first order kinetics (C ¼ 9.9917e -0.187 t , R 2 ¼ 0.994). The half-life was about 3.6 hours. Qualitative study on photolysis products of clothianidin were taken by checking all total ion spectra of different sample time. A total of

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... eight products was found in this study. The structure of each product was determined by the total ion spectrometry spectrum and daughter-scan spectrum. The mechanism of photodegradation of this pesticide included radical denitration, nucleophilic substitution, and rearrangement, ring-open, and ring-close. Through the analysis of the change of every product and the mass information, the photolysis pathway was drawn. From this study, products of V, VI, and VII seemed more stable than clothianidin.