Abstract: Objective: To develop a method to quantitatively analyze the residues of six pesticides (carbendazim, tricyclozole, bensulfuron methyl, triazophos, chlorpyrifos and carbosulfan) in paddy and rice by quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and to propose a quantitative model for pesticide residues using Minitab software. Methods: Positive samples were prepared by spraying pesticide mixture solution on paddy and rice, and stored at constant temperature and relative humidity conditions simulating those in grain depot. Temperature and relative humidity as key variables were set at different levels, namely 20, 30, 40 and 50 ℃; and 50%, 60%, 70% and 80%. Results: The calibration curves for the six pesticides showed good linearity in the concentration range of 5.0–1 000.0 μg/L with correlation coefficient (R2) greater than 0.999 0, the detection limits were in the range of 0.000 1–0.005 mg/kg, the average spiked recoveries were in the range of 84.02%–103.24%, and the precision, expressed as relative standard deviation (RSD), was in the range of 3.65%–8.29%. Therefore, the QuEChERS-UPLC-MS/MS method can meet the requirements of the analysis and detection of pesticide residues. The quantitative model of pesticide degradation during the whole process from paddy to rice, developed by the processing factors investigated, showed R2 value above 0.769. Among them, the R2 values for carbendazim, bensulfuron, triazophos and chlorpyrifos in paddy were greater than 0.9, and those for triazophos and butachlor in rice were also greater than 0.9, indicating good fitness. The residues of the six pesticides in the positive samples gradually decreased with storage time, and the degradation rate of pesticide residues changed with storage environment. Conclusion: The QuEChERS-UPLC-MS/MS method is simple, rapid, and accurate and suitable for the detection of the six pesticide residues in paddy and rice. The quantitative model of pesticide degradation during the whole process from paddy to rice is well fitted, and the degradation patterns of pesticide residues in paddy and rice under different storage conditions are different. This study has important significance to improve the comprehensive benefits of the grain industry.

Key words: paddy and rice; pesticide residues; storage environment; ultra-high performance liquid chromatography-tandem mass spectrometry; quick, easy, cheap, effective, rugged and safe