Photolytic degradation of the insecticide thiamethoxam in aqueous medium monitored by direct infusion electrospray ionization mass spectrometry.
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.
de Urzedo
Ana P F M
AP
Department of Chemistry, Federal University of Minas Gerais, Belo Horizonte, MG 31270-901, Brazil.
Diniz
M E R
ME
Nascentes
Clésia C
CC
Catharino
Rodrigo R
RR
Eberlin
Marcos N
MN
Augusti
Rodinei
R
D007306:Insecticides / Q000737:chemistry* / Q000528:radiation effects*; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000737:chemistry / Q000528:radiation effects*; D010078:Oxazines / Q000737:chemistry / Q000528:radiation effects*; D010777:Photochemistry; D010782:Photolysis; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods; D000077922:Thiamethoxam; D013844:Thiazoles / Q000737:chemistry / Q000528:radiation effects*; D014867:Water
D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010078:Oxazines; D013844:Thiazoles; D014867:Water; D000077922:Thiamethoxam