Effective extraction method for determination of neonicotinoid residues in tea.

Sample preparation using an absorbent for removal of polyphenols and a solid-phase extraction (SPE) cartridge for cleanup followed by high-performance liquid chromatography (HPLC) has been investigated for the simultaneous determination of eight neonicotinoid insecticides (dinotefuran, nitenpyram, thiamethoxam, imidacloprid, clothianidin, imidaclothiz, acetamiprid, and thiacloprid). After tea samples were soaked with water and extracted with acetonitrile, sample extracts were treated with an appropriate amount of polyvinylpolypyrrolidone (PVPP) to effectively remove polyphenols. The treated extract was cleaned up with a Carb-PSA cartridge. Neonicotinoid insecticides were eluted with acetonitrile from the cartridge and dried. The extract was redissolved with methanol/water (1:9, v/v) and analyzed by conventional HPLC coupled with an ultraviolet detector. The recoveries of eight neonicotinoid insecticides in tea samples were 71.4-106.6% at 0.1-1.0 mg kg(-1) spiked levels. Relative standard deviations were <10% for all of the recovery tests. The established method was simple, effective, and accurate and could be used for monitoring neonicotinoid insecticides in tea.

Comparison of the dissipation behaviour of three neonicotinoid insecticides in tea.

The dissipation behaviour of three neonicotinoids - thiamethoxam, imidacloprid and acetamiprid - was compared in tea shoots, in Chinese green and black tea, and after tea infusion in hot water. The simple and rapid analytical procedures for the quantification of these three residues in these matrices were developed using HPLC with ultraviolet (UV) detection. Degradation rates in tea shoots of neonicotinoids applied in either recommended or double dosages followed first-order kinetics, with half-lives of 1.62 or 1.58 days for thiamethoxam, of 2.45 or 2.67 days for imidacloprid, and of 3.24 or 3.85 days for acetamiprid, respectively. Through harvest and processing the residue retentions for thiamethoxam, imidacloprid and acetamiprid were 85.0%, 84.1% and 70.6% of the initial dosages in green tea, and 77.1%, 52.4% and 57.4% in black tea. These three residues all showed high transfer rates through green or black tea brewing of 80.5% or 81.6% for thiamethoxam, of 63.1% or 62.2% for imidacloprid, and of 78.3% or 80.6% for acetamiprid. Waiting periods between the last application and harvest of at least 12, 17 and 20 days were suggested for thiamethoxam, imidacloprid and acetamiprid, respectively, after application at their recommend dosages to ensure levels below a maximum residue limit (MRL) of 0.05 mg kg(-1).