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Photolytic degradation of the insecticide thiamethoxam in aqueous medium monitored by direct infusion electrospray ionization mass spectrometry
Author(s) -
de Urzedo Ana P. F. M.,
Diniz M. E. R.,
Nascentes Clésia C.,
Catharino Rodrigo R.,
Eberlin Marcos N.,
Augusti Rodinei
Publication year - 2007
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.1204
Subject(s) - chemistry , aqueous solution , photodegradation , electrospray ionization , mass spectrometry , electrospray , ion , ionization , chromatography , analytical chemistry (journal) , organic chemistry , catalysis , photocatalysis
Photodegradation of the insecticide thiamethoxam (1), 3‐[(2‐chloro‐5‐thiazolyl)methyl]tetrahydro‐5‐methyl‐ N ‐nitro‐4H‐1,3,5‐oxadiazin‐4‐imine, in an aqueous medium was monitored by electrospray ionization mass spectrometry in the positive ion mode, ESI(+)‐MS. An aqueous solution of (1) was incessantly exposed to a UV radiation source and aliquots were taken after reaction times of 1, 2, 3, and 4 h. Analysis by GC/NCI‐MS revealed that (1) was continuously degraded under these experimental conditions. However, the total organic carbon (TOC) content remained practically constant during the exposition period, thereby indicating that 1 was not mineralized but continuously converted into other compounds. ESI(+)‐MS monitoring revealed that whereas the intensity of the ions of m / z 292/294 ([1 + H] + ) constantly decreased, there was the emergence of other ions of m / z 247/249, 197, 168, and 116 whose intensities simultaneously increased. Their structures were proposed on the basis of: (1) the data of their ESI(+)‐MS/MS; (2) their high resolution m / z values; and (3) a plausible reactivity of the thiamethoxam molecule exposed to UV radiation in aqueous solution. Finally, these data allowed us to suggest a reaction route for the photodegradation of 1 in an aqueous medium. Copyright © 2007 John Wiley & Sons, Ltd.