Determination of Nine Botanical Pesticide Residues in Tea by UHPLC-MS/MS

The problem of pesticide residues in tea has always been the most concerned by consumers. In order to reduce the amount of pesticide residues in tea, tea farmers gradually changed from chemical pesticides to botanical pesticides to control diseases and insect pests while adopting physical control. Scientists all over the world were also continuously studying the control effects of various botanical pesticides on tea plant diseases and insect pests. At present, there were many analytical methods to study pesticide residues in tea, while there were few researches on botanical pesticides in tea leaves. QuEChERS method is quick, easy, cheap, effective, rigged and safe, which was the most commonly used sample pretreatment in the detection of pesticide residues. An efficient method was developed for the determination of 9 botanical pesticide residues (nicotine, rotenone, matrine, azadirachtin A, azadirachtin B, veratrine, berberine, capsaicins and dihydrocapsaicin) in tea by QuEChERS-ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The samples were ultrasonically extracted with 10 mL acetonitrile containing 0.5% formic acid. After centrifugation, the supernatant extract was cleaned up by QuEChERS method with primary secondary amine (PSA). PSA does not adsorb target compounds but can remove interferences in tea, effectively reducing the interference of matrix effect. The target analytes were separated on HSS T3 C18 column (2.1 mm×50 mm×1.8 μm) using gradient elution of 0.002 mol/L ammonium acetate water (containing 0.02% formic acid) and methanol, detected by MS/MS system under positive electro-spray ionization (ESI+) mode with multiple reaction ion monitoring (MRM). Due to the strong polarity of nicotine and matrine and the serious interference of matrix effect, the stable isotope internal standard method was used for quantification, and the other target objects were used for quantification by external standard method. The matrix matched standard solutions of 9 botanical pesticides showed good linear relationship with the correlation coefficients (r) more than 0.999. The recoveries of 9 botanical pesticides were in the range of 83.7%-117.8% with relative standard deviations(RSDs) no more than 10%. The limits of detection (LODs) and the limits of quantification (LODs) were 2.0-3.0 μg/kg and 5.0-10.0 μg/kg, respectively. The method is easy, quick and high sensitive, and is suitable for quick determination of botanical pesticide residues in tea. Among the 157 tea samples on the market, only two samples were detected for nicotine, which met the EU’s requirements for nicotine limit, and no other compounds were detected.