Simultaneous determination of eight carbamate pesticide residues in tomato, rice, and cabbage by online solid phase extraction/purification-high performance liquid chromatography-tandem mass spectrometry

Carbamate pesticides are a class of synthetic pesticides having wide antimicrobial spectrum, good insecticidal efficacy, and a short residual period. These pesticides are used in agriculture, forestry, and animal husbandry. Their widespread use in the last two decades has led to the existence of drug residues in the environment, which are transferred to food, thereby raising concerns regarding the potential threat to human health. Rapid and accurate detection of carbamate pesticide residues in food is of great significance for food safety, and this requires pretreatment to purify the target components and maximize the accuracy and precision of the analysis. A rapid and accurate analytical method based on online solid phase extraction/purification-high performance liquid chromatography-tandem mass spectrometry (online SPE-HPLC-MS/MS) was established for the determination of eight carbamate pesticides in tomato, rice, and cabbage. About 5.0 g of tomato (without water), 2.0 g of cabbage, and 2.0 g of rice (mixed with 3 mL of water) were vortexed at 1000 r/min for 1 min. After adding 2 g of sodium chloride and 10 mL of acetonitrile containing 0.5% (v/v) formic acid, the samples were extracted and centrifuged. The supernatants were combined after the samples were extracted again. The reconstituted solutions were then purified on a CAPCELL PAK C18 column (50 mm×2.0 mm, 15 μm). When the volume ratio of 0.1% (v/v) formic acid aqueous solution and acetonitrile (used as the mobile phases) was 90∶10 and 35∶65, the eight carbamate pesticides could be completely adsorbed and eluted. The carbamate pesticides were separated on an ACQUITY UPLC CSH C18 column (100 mm×2.1 mm, 1.7 μm) under gradient elution and analyzed in the multiple reaction monitoring (MRM) mode with positive electrospray ionization (ESI+). Under the optimum conditions, the calibration curves of the eight carbamate pesticide residues showed good linearity (r>0.995) within their respective linear ranges. The limits of quantification (LOQs) and limits of detection (LODs) were in the range of 0.05-1.0 ng/mL (S/N=10) and 0.01-0.3 ng/mL (S/N=3). The recoveries were in the range of 73.76%-112.32% at three spiked levels (2, 10, and 20 ng/mL), with relative standard deviations of 1.28%-13.14% (n=6). The online purification method showed better enrichment and purification ability for the target substances than did the offline purification method and greatly improved the pretreatment efficiency. The loading and purification could be completed within 12 min. The developed method has the advantages of high recovery rate, good reproducibility, accuracy, rapidness, sensitivity, and environment friendliness. It can be used for the determination of the eight carbamate pesticides in plant foods, such as tomato, rice, and cabbage.