Abstract
A novel method was developed for the simultaneous determination of mesotrione and its metabolite(4-methylsulfonyl-2-nitrobenzoic acid, MNBA) in maize by ultra performance liquid chromatography coupled with tandem mass spectrometry(UPLC-MS/MS). The samples were extracted with acetonitrile-water (50:50, V/V) solutions and an aliquot of the extract was acidified to pH 2 with formic acid and then cleaned-up by Oasis HLB cartridge. The residues were eluted from cartridge with methanol- diethyl ether (70:30, V/V). The elutions were evaporated to appropriately dry under a stream of nitrogen, dissolved in 2 mL acetonitrile-1 mmol/L ammonium acetate (75:25, V/V). The residues were analyzed by mass spectrometry with negative ion mode using multiple-reaction monitoring (MRM) and quantification was achieved by matrix calibration. The method had a good linear correlation (correlation coefficient was above 0.99) in the range of 1-200 μg/L. The average recoveries of mesotrione and MNBA were 83.8%-101.1% at spiked level between 5 μg/kg and 50 μg/kg with the relative standard deviation (RSD) between 5.3% and 12.8%. The limits of quantification for mesotrione and MNBA were 1.0 and 2.0 μg/kg, respectively.
