Determination of flumorph and dimethomorph residues in vegetables by improved QuEChERS-gas chromatography-mass spectrometry

To determine the residues of flumorph and dimethomorph in vegetables, a method was established with improved QuEChERS-gas chromatography coupled to mass spectrometry (GC-MS). With acetonitrile as the extraction solvent, the samples were pretreated with the improved QuEChERS method including extraction, salting-out and purification processes. Then all the sample extracts were analyzed with GC-MS in selected-ion monitoring (SIM) mode, and quantified by matrix-matched standard solution in external standard method. Under electron ionization conditions, the analysis was carried out with a capillary column (DB-5 MS, 30 mx 0.25 mmx0.25 mu m) at a flow rate of 1.1 mL/min. The quantitation was performed to detect ions of m/z 285, 371, 165 for flumorph and m/z 301, 387, 165 for dimethomorph. Good linearity was obtained in the range of 10-1000 mu g/kg for both pesticides with correlation coefficients greater than 0.999. The recovery experiments were carried out by spiking blank samples of ginger, tomato, carrot, spinach, cabbage and tremella at the three levels of 10, 20 and 100 mu g/kg. For both pesticides in different matrices, the limits of detection (S/ N= 3) were in the range of 0.67-2.42 mu g/kg. The average recoveries of flumorph and dimethomorph ranged from 71% to 116% with the relative standard deviations (RSDs) in the range of 1.8% -14.7%. Meanwhile, the pyrolysis mechanism and matrix effect for the determination of flumorph and dimethomorph in vegetables were investigated in this study. The method is simple, rapid and accurate, and can be used for the routine analysis of flumorph and dimethomorph in vegetables.