Analysis of Sulfonylurea Herbicides in Soil Water at Sub-Part-Per-Biffion Levels by Electrospray Negative Ionization Mass Spectrometry Followed by Confirmatory Tandem Mass Spectrometry

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Abstract
Liquid chromatography coupled to mass spectrometry (MS) with an electrospray ionization interface was used to analyze 4 sulfonylurea herbicides: chlorsulfuron, metsulfuron-methyl, thifensulfuron-methyl, and tribenuron-methyl. Fortified soil water was acidified to pH 4.5 (the pH was maintained neutral for tribenuron-methyl because it rapidly hydrolyzes at low pH) and extracted on Ci8 cartridges. Extracts were cleaned up on silica cartridges. MS analysis was accomplished by selected ion monitoring of the deprotonated molecular ion in negative-ion mode. The 4 compounds were quantitated with the external standard technique based on the integrated abundance of the molecular ion [M - H]~. Good reproducibility and high sensitivity (detection limits for the 4 compounds were between 0.002 and 0.005 μg/L) were achieved. Tandem MS (MS/MS) in selected reaction monitoring mode on a characteristic product ion (m/z139 for chlorsulfuron, metsulfuron-methyl, and thifensulfuron-methyl; nvzA53 for tribenuronmethyl) was used as confirmatory method. High sensitivity was maintained also with MS/MS, making it possible to identify sulfonylurea herbicides at very low concentrations.

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