A method for the simultaneous detection of the residues of nine novel pesticides in plant-derived foods was developed by quick, easy, cheap, effective, rugged, and safe (QuEChERS) pretreatment combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The pesticides included flutianil, ipflufenoquin, mandestrobin, pyriofenone, benzpyrimoxan, isocycloseram, pyflubumide, fluazaindolizine, tolpyralate. Samples were extracted with 1% formic acid in acetonitrile followed by salting-out and phase separation using anhydrous magnesium sulfate, sodium chloride and a mixture of sodium citrate and sodium dihydrogen citrate. The extracts were purified with a mixture of N-propyl-ethylenediamine (PSA), octadecyltrimethoxysilane (C₁₈) and graphitized carbon black (GCB). The chromatographic separation was accomplished on a T3 column (100 mm × 2.1 mm, 1.8 µm) by gradient elution using a mobile phase consisting of 5 mmol/L ammonium acetate solution (containing 0.1% formic acid) and acetonitrile. The detection was carried out in the multiple reaction monitoring (MRM) mode, and the quantification was performed using a matrix-matched standard curve. The results showed that the calibration curves for all analytes exhibited a good linear relationship in the tested concentration range (R² ≥ 0.995), the limit of quantification (LOQ) was 0.005 to 0.01 mg/kg. At three spiked levels of 0.005, 0.01 and 0.05 mg/kg, the average recoveries ranged from 73.9% to 118.1%, with relative standard deviation (RSD) ranging from 0.8% and 12.8% (n = 6). This method is rapid, accurate, sensitive, and suitable for simultaneous quantification of these novel pesticides in plant-derived foods.

A gas chromatography-tandem mass spectrometry (GC-MS/MS) with stable isotope dilution (SID) method was established for the determination of dioxins (PCDD/Fs) and dioxin like polychlorinated biphenyls (DL-PCBs) in pork. The sample was extracted by Soxhlet extraction, defatted using acidified silica gel, and purified by sequential chromatography on a multi-layer silica gel column, an alkaline alumina column and an activated carbon column. PCDD/Fs- and DL-PCBs-rich fractions were collected separately, concentrated and redissolved for GC-MS/MS analysis. The influence of defatting method and fat content on the purification efficiency was investigated, and the blank contamination source of the system was discussed. The results showed that gel permeation chromatography (GPC) degreasing had a great influence on the recovery of PCDD/Fs and DL-PCBs, and acidified silica gel degreasing was more suitable for the analysis and detection of ultra-trace dioxins. The major blank pollution source of the dioxin detection system was the Soxhlet extractor. The recoveries for internal standard were 45.3%–122.4% with relative standard deviation (RSD) of 1.0%–14.7%. The recoveries for the analytes were 64.9%–118.8% with RSD of 1.1%–14.7%. Both the linearity and limit of detection (LOD) met the requirements of the national standard of China GB 5009.205-2013. The proposed method is suitable for the determination of PCDD/Fs and DL-PCBs in actual pork samples.