Abstract
Neonicotinoid insecticides play an important role in the prevention and control of pests in crops, such as rice, wheat, corn, and vegetables, because of their broad spectrum, high efficiency, low toxicity, and low residue formation. However, their widespread use poses potential threats to the environment and human health. Cycloxaprid and paichongding are two new classes of neonicotinoid insecticides. The National Food Safety Standard Maximum Residue Limits for Pesticides in Foods (GB 2763) specifies the maximum residue limits for paichongding and cycloxaprid in rice, brown rice, wheat, and cabbage. However, the established limits are only temporary. In addition, no detection standards have yet been specified, and no relevant standards have been established in China. Therefore, establishing a method for analyzing cycloxaprid and paichongding residues in food is of particular importance. In this study, an optimized method was established to determine the residues of cycloxaprid and two noncorresponding isomers of paichongding in plant foods using ultra performance liquid chromatography-tandem mass spectrometry. The chromatographic conditions, matrix extraction methods for dried fruits and tea, and amounts of the purification materials C(18), PSA, GCB, and anhydrous magnesium sulfate were optimized. The pesticides were extracted using an acetonitrile solution and separated from water with the addition of sodium chloride. The samples were centrifuged at 5000 r/min for 5 min, after which 1.00 mL of the supernatant was purified using 150 mg of anhydrous magnesium sulfate, 25 mg of C(18), 25 mg of PSA, and 10 mg of GCB. Cycloxaprid and paichongding were separated on a ACQUITY UPLC BEH C(18) chromatographic column (100 mm×2.1 mm, 1.7 μm) via gradient elution with 0.1% formic acid aqueous solution containing 5 mmol/L ammonium formate-acetonitrile as the mobile phase, and detected in electrospray positive ionization mode coupled with multiple-reaction monitoring (MRM) mode. Quantitative analysis was performed using an external standard method. Cycloxaprid and paichongding demonstrated good linear relationships within their respective concentration ranges, and the corresponding correlation coefficients were all above 0.99. The limits of detection (S/N=3) and quantification were 0.05 μg/kg and 0.01 mg/kg, respectively, which meet the requirements specified in GB 2763-2021 and GB 2763.1-2022. The established method was used to validate the recoveries of cycloxaprid and paichongding spiked in foods of plant origin, such as paddy, brown rice, wheat, rice, peanut, raisin, cabbage, lettuce, green bean, tomato, potato, shiitake mushroom, apple, citrus, and tea substrates, at three levels. The spiked levels covered the limit levels specified in GB 2763-2021 and GB 2763.1-2022. The mean recoveries of the target substances added to the 15 substrates at concentrations of 1, 2, and 10 times the LOQ or the limit values specified in GB 2763-2021 and GB 2763.1-2022 were distributed between 78% and 110%, and the RSDs were within the range of 0-12.8%. One hundred batches of fruit and vegetable samples were analyzed using the developed method, and the results showed that the selected samples were not contaminated with either cycloxaprid or paichongding. The proposed method is simple, sensitive, and universal, and has wide coverage. Thus, it can be used as a confirmatory and quantitative detection method for epoxidine and piperidine in foods of plant origin.