Comparison of the Metabolic Behaviors of Six Systemic Insecticides in a Newly Established Cell Suspension Culture Derived from Tea ( Camellia sinensis L.) Leaves.

The use of an in vitro cell suspension to study insecticide metabolism is a simpler strategy compared to using intact plants, especially for a difficult matrix such as tea. In this study, a sterile tea leaf callus was inoculated into B5 liquid media with 2,4-dichlorophenoxyacetic acid (2,4-D, 1.0 mg L-1) and Kinetin (KT, 0.1 mg L-1). After 3-4 subcultures (28 days each), a good cell suspension was established. Utilizing these cultures, the metabolic behaviors of six insecticides, including two organophosphates (dimethoate, omethoate) and four neonicotinoids (thiamethoxam, imidacloprid, acetamiprid, and imidaclothiz) were compared. The results showed that thiamethoxam, dimethoate, and omethoate were easily metabolized by tea cells, with degradation ratios after 75 days of 55.3%, 90.4%, and 100%, respectively. Seven metabolites of thiamethoxan and two metabolites of dimethoate were found in treated cell cultures using mass-spectrometry, compared to only two metabolites for thiamethoxam and one for dimethoate in treated intact plants.

Optimized combination of dilution and refined QuEChERS to overcome matrix effects of six types of tea for determination eight neonicotinoid insecticides by ultra performance liquid chromatography-electrospray tandem mass spectrometry.

Liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) is a primary tool for analysis of low volatility compounds in complex matrices. However, complex matrices, such as different types of tea, complicate analysis through ionization suppression or enhancement. In this study, sample preparation by a refined QuEChERS method combined with a dilution strategy removed almost all matrix effects caused by six types of tea. Tea samples were soaked with water and extracted with acetonitrile, cleaned up with a combination of PVPP (160mg) and GCB (20mg), and dried. Dried extracts were diluted with 20mL acetonitrile/water (15:85, v/v) before analysis by UPLC-MS/MS. The average recoveries of eight neonicotinoid insecticides (dinotefuran, nitenpyram, thiamethoxam, imidacloprid, clothianidin, imidaclothiz, acetamiprid, and thiacloprid) ranged from 66.3 to 108.0% from tea samples spiked at 0.01-0.5mgkg(-1). Relative standard deviations were below 16% for all recovery tests. The limit of quantification ranged from 0.01 to 0.05mgkg(-1).