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.
Determination of urinary catecholamines and metanephrines is important for diagnosis of pheochromocytoma. Liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed for the determination of catecholamines and metanephrines in human urine using deuterated internal standards (IS). In this method, 1000 µL of urine samples were treated by liquid-liquid extraction using ethyl acetate and subjected to LC-MS/MS analysis using positive electrospray ionization (ESI+). A BDS HYPERSILTM C18 column (125 mm × 3 mm, 3 µm) was used and mobile phase was water:methanol (98:2, v/v) with 0.25% of formic acid at 200 µ L min
−1
. The method has a chromatographic running time of approximately 10 min. The average of recovery was 92.9-106.1% for epinephrine, 94.6-107.7% for norepinephrine, 98.0-108.8% the dopamine, 94.2-105.1% the metanephrine, 97.0-106.0% for normetanephrine. The precision was lower than 7.0% for all analytes. Furthermore, this method has been implemented successfully in routine laboratory due to its easy execution and excellent precision.
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