OBJECTIVE An improved QuEChERS method was established and verified for simultaneous determination of isoxaflutole and its metabolites diketonitrile and benzoic acid analogue residues in corn and plants. This method was mainly used to study the digestion rule and final residue level of isoxaflutole and its metabolites in corn and plants. It was hoped that the safe use of isoxaflutole in corn can be achieved eventually. METHOD The method was completed by means of ultra‐performance liquid chromatography with triple quadrupole mass spectrometry. The extraction of the target substance was through acetonitrile solution containing 1% acetic acid, and the purification was through primary secondary amine, octadecylsilane and graphitized carbon black sorbent. RESULTS In the method, the quantitative limits and detection limits of the three analytes were 0.005–0.01 and 0.001–0.003 mg kg−1 respectively. The half‐life of isoxaflutole in the plants in Shandong and Anhui was 36.4 and 42.1 days respectively, and the digestion dynamics all conformed to the first‐order kinetics. The final residues of isoxaflutole in green corn and mature corn were less than 0.02 mg kg−1 of the maximum residue limit set by the Codex Alimentarius Commission. CONCLUSIONS The residual amount of isoxaflutole in corn and plants at harvest time was acceptable when isoxaflutole was applied once at a dose of 121.5 g a.i. ha−1. © 2021 Society of Chemical Industry.
Through field trials and residue analysis, the dissipation behaviour and final residue levels of sodium nitrophenol on jujube were clarified to provide a basis for its safe application and the development of maximum residue limits. The samples were extracted with acetonitrile, cleaned up by a hydrophilic-lipophilic balanced solid-phase extraction column, determined by ultra-high LC-tandem mass spectrometry and quantified by the external standard method. The mean recoveries of sodium 5-nitroguaiacolate, sodium o-nitrophenol and sodium p-nitrophenol were 88.9%-103.8%, with relative standard deviations less than 13.6% at 0.002-0.2 mg/kg spiked levels. Sodium nitrophenol in jujube was dissipated according to the first-order kinetic equation with half-lives of 12.7-17.4 days. At a harvesting interval of 7 days, the residues of sodium nitrophenol in jujube were lower than the limit of 0.03 mg/kg established by the European Food Safety Authority. Residues of jujube were acceptable at a harvest interval of 7 days when sodium nitrophenol was sprayed twice at 9.0 mg/kg with an interval of 7 days. Therefore, the safety interval for sodium nitrophenol application on jujube can be set as 7 days.
A method was developed for the quantitative determination of cyanamide in grapes and cherries by liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with dansyl chloride (DNS) precolumn derivatization. First, the samples were homogenized, and then extracted with ethyl acetate under ultrasonication. The water was removed using anhydrous sodium sulfate, and the extract was concentrated and derivatized with dansyl chloride under alkaline condition. The separation was performed on a Shimadzu Shim-pack XR-ODS column (75 mm×2.0 mm, 1.6 μm) with the mobile phases of methanol and 2 mmol/L ammonium acetate aqueous solution (containing 0.05% (v/v) formic acid) in a gradient elution mode. The identification and quantification of cyanamide were carried out by MS/MS in positive electrospray ionization (ESI) and multiple reaction monitoring (MRM) mode. The calibration curves showed good linearities in the range of 0.01-1.0 mg/L with the correlation coefficients not less than 0.9990. The average recoveries of cyanamide spiked at 0.01, 0.05 and 1.0 mg/kg in cherries and grapes were between 75% and 81%, and the relative standard deviations (RSDs) were between 6.5% and 9.8%. Both the limits of quantification (LOQs) of the analytes were 0.01 mg/kg. The method is simple, rapid, accurate and suitable for the confirmation and quantification of cyanamide in cherries and grapes.
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