No abstract

A rapid UPLC-ESI (+)-MS/MS method was developed and validated for simultaneous determination of eight neonicotinoid insecticides (dinotefuran, nitenpyram, thiamethoxam, clothianidin, imidacloprid, acetamiprid, thiacloprid and imidaclothiz) in tea samples based on a refined QuEChERS extraction method. In order to eliminate the matrix effect and obtain satisfactory recoveries, an inexpensive and excellent absorbent material, polyvinylpolypyrrolidone (PVPP), was used to eliminate polyphenols from tea matrices. Further, combinations of PVPP and the commonly used sorbents PSA and GCB were investigated in this study.The optimized 'quick, easy, cheap, effective, rugged and safe' protocol is briefly described as follows. Tea samples were soaked in water and extracted with acetonitrile. Sample extracts were treated with 400 mg PVPP to remove polyphenols from tea matrices, and then cleaned up with a combination of PSA (25 mg), GCB (100 mg) and C18 (50 mg). Finally, the dried extract was dissolved in acetonitrile/water (15 : 85, v/v) and analyzed by UPLC-MS/MS. The recovery ratios from tea for eight neonicotinoid insecticides ranged from 60-109% at 0.01-0.5 mg kg À1 spiked levels. Relative standard deviations were <15.4% for all of the recovery tests. The limit of quantification was below 0.01 mg kg À1 . The developed method was simple, effective, and sensitive. This method should prove to be highly useful for monitoring neonicotinoid insecticides in commercial tea products.

BACKGROUND The use of pesticides during tea plant cultivation helps agricultural production and prevents and controls pests, diseases and weeds. It is of the utmost importance to balance pesticide application with tea quality, safety and consumer health. The uptake of pesticides into plants may lead to the presence of residues that are hazardous to human health, especially for some foliar‐applied insecticides. The movability or penetration behavior of a pesticide remains unknown after it has been sprayed on a tea leaf. RESULTS Two organophosphate (acephate, trichlorfon) and three neonicotinoid pesticides (imidacloprid, thiamethoxam and acetamiprid) were confirmed with respect to their removal from the treated fresh leaves of tea saplings via washing in a phytotron. Four of the targets have little penetrative ability into tea leaves, mainly existing (> 92%) on the tea leaf surface, except for trichlorfon (> 70%), for 30 days. With higher vapor pressures, trichlorfon and acetamiprid had relatively higher penetration ratios of 8.63–29.60% and 0.28–8.03% respectively. Two organophosphate insecticides were found to degrade more quickly, with lower final amounts of residues on and in the whole leaf compared to the neonicotinoid pesticides. In a field test, these residues could be reduced by 45–72% after a pre‐harvest interval of 3 days, and by 16–89% after 7 days, when the fresh tea shoots were sprayed with 2 or 4 L m−2 water. CONCLUSION Pesticides with different structures have different penetration abilities on the tea leaf surface, and some pesticides in commercial tea can be reduced by spraying with water before fresh leaves are picked. © 2020 Society of Chemical Industry