Dimesulfazet can control annual and perennial sedges in rice paddies. Here we assessed its mode of action. We performed a phenotype assay of Arabidopsis, conducted a metabolomic analysis of Echinochloa crus-galli, and analyzed the endogenous concentration of very long-chain fatty acids (VLCFAs) in Schoenoplectiella juncoides. Dimesulfazet treatment caused curling and greening symptoms in the leaves and fiddlehead-like symptoms in the inflorescences of Arabidopsis. These symptoms were visually indistinguishable from those caused by flufenacet and benfuresate, which belong to Herbicide Resistance Action Committee (HRAC) Group 15. We performed GC-MS/MS analysis of primary metabolites and LC-MS analysis of lipids in the herbicide-treated E. crus-galli, followed by Orthogonal Partial Least Squares Discriminant Analysis clustering. The results showed that dimesulfazet belongs to the HRAC Group 15 cluster. The endogenous concentrations of C24:0, C26:0, and C28:0 decreased in dimesulfazet-treated plants as compared to those in the control. Overall, the mode of action of dimesulfazet involves the inhibition of VLCFA biosynthesis.

The matrix effects (ME) in simultaneous analysis of pesticide residue using liquid chromatography-tandem mass spectrometry (LC-MS/MS) were evaluated by comparing the slopes of matrix-matched and reagent-only calibrations of four types of vegetable samples. Both the sampling and measurement variances of the ME were also determined using one-way analysis of variance. Substantial ion suppression (ME<−20%) was observed in komatsuna, spinach, and tomato when a modified Japanese official method was implemented. The ME magnitude varied significantly due to sample variability for some pesticides, but it varied by no more than 4% as a result of analytical procedure variance. This study also showed that the addition of stable isotope-labeled internal standards at low concentrations improved the recovery of pesticides from samples at various residue levels. The findings of this study highlight the importance and practical application of internal standards and the matrix-matched calibration method in residue analysis using LC-MS/MS.

A simple fluorescent “on-off” system that can be utilized for the selective identification and determination of paraquat (PQ) is presented herein. ¹H NMR spectroscopic data indicated that in aqueous solution the alkaloid palmatine can be partially encapsulated within the cucurbit[7]uril (Q[7]) cavity, whereby a stable 1 : 1 host–guest inclusion complex is formed. Other characterization techniques including mass spectrometry, UV-Vis and fluorescence spectroscopy also provided further evidence, and the host-guest inclusion complex was found to exhibit reasonable fluorescence intensity. It is noteworthy that the addition of PQ resulted in quenching the fluorescence of the host-guest inclusion complex, whereas the presence of 12 other pesticides did not significantly affect the fluorescence intensity. Given the linear relationship between the intensity of the fluorescence and the PQ concentration, the PQ concentration in aqueous solution was easily detected. Thus, a new method for identifying and determining the fluorescence quenching of PQ has been developed in this work.