Simultaneous determination of fungicides and carbamates in tobacco by ultra performance convergence chromatography-tandem mass spectrometry coupled with modified QuEChERS

Simultaneous determination of enantiomer residues of metalaxyl and its metabolite metalaxyl acid in animal muscle tissues by chiral liquid chromatography-tandem mass spectrometry

The toxicity of the two enantiomers of metalaxyl is significantly different and, for food safety concerns, stereoselective analysis of its residues is extremely important in animal muscle tissues. Herein, a simple, sensitive and reproducible method for the simultaneous stereoselective analysis of metalaxyl and its metabolite metalaxyl acid in animal-derived foods has been established based on mixed-mode anion exchange solid phase extraction and chiral liquid chromatography-tandem mass spectrometry. Under the optimized separation and sample pretreatment conditions, good linearity (r > 0.99) was obtained for four target analytes in four animal muscle tissues including bovine, chicken, swine and fish. Mean recoveries of all enantiomers in muscle tissue samples were 89.5-110.3 % with relative standard deviations below 12.4 %. The limits of quantification of the analytes were 0.3-1.0 µg/kg. The proposed method provides an effective means to monitor the enantiomer residues in real samples whether using highly active R-metalaxyl or racemic mixture drugs.

Development of a new and facile method for determination of chlorpyrifos residues in green tea by dispersive liquid-liquid microextraction

In this work a simple, rapid, and environmentally friendly method has been established for the determination of chlorpyrifos residue in green tea by dispersive liquid-liquid microextraction and gas chromatography-flame photometric detection. Some experimental parameters that influence extraction efficiency, such as the kind and volume of disperser solvents and extraction solvents, extraction time, addition of salt and pH, were investigated. And the optimal experimental conditions were obtained, quantitative analysis was carried out using external standard method. The correlation coefficient of the calibration curves was 0.999 with in 0.05 mg/kg to 5 mg/kg. The results showed that under the optimum conditions, the enrichment factors of the chlorpyrifos was about 554.51, the recoveries for standard addition fell in the range from 91.94 to 104.70% and the relative standard deviations was 4.61%. The limit of quantification of chlorpyrifos in green tea was 0.02 μg/mL at the signal/noise ratio of 3.

Simultaneous analysis of multiple pesticide residues in tobacco by magnetic carbon composite-based QuEChERS method and liquid chromatography coupled to quadrupole time-of-flight mass spectrometry

Magnetic carbon composite (Fe3O4@C) was synthesized and applied as a reversed-dispersive solid-phase extraction sorbent for the simultaneous analysis of 40 pesticide residues in tobacco by ultrahigh-performance liquid chromatography coupled to quadrupole time-of-fight mass spectrometry. Compared to the traditional QuEChERS method, the optimized Fe3O4@C simplified clean-up process and exhibited better clean-up capability than conventional sorbents. The pesticides were qualitatively identified by accurate mass of protonated molecules, fragment ions, isotopic peak clusters, and retention time, and quantitatively determined by matrix-matched external standard method. Good linearity of the proposed method was obtained with R value greater than 0.997 for all target pesticides at concentration levels of 2-200 µg/L. The limit of detection ranged from 0.14 to 2.67 µg/kg. The recoveries and relative standard deviations of all target pesticides at three spiked concentrations of 20, 50 and 200 µg/kg were in the ranges of 80.8%-113.3% and 0.6%-16.3%, respectively. Compared with the reported methods for the analysis of multiple pesticide residues in tobacco, the proposed method has the advantages of simple to operate, high clean-up ability and less time-consuming in clean-up process.