Simultaneous Determination of Neonicotinoid Insecticides and Metabolites Residues in Milk and Infant Formula Milk Powder by EMR-Liquid Chromatography-Tandem Mass Spectrometry

An analytical method based on enhanced matrix removal–lipid liquid chromatography–tandem mass spectrometry (EMR-LC–MS/MS) was developed for the determination of neonicotinoid insecticides and metabolites residues (imidacloprid (IMI) and its metabolites imidacloprid-urea (IMI-U), imidacloprid-olefin (IMI-O), acetamiprid (ACE) and its metabolite N-desmethyl acetamiprid (IM 2–1), dinotefuran (DIN) and its metabolite [1-methy1-3(tetrahydro-3-furylmethy1) urea (DIN-UF), thiacloprid (THIA), thiamethoxam (TMX), clothianidin (CLO, metabolite of thiamethoxam), and flupyradifurone (FLU)) in milk and infant formula milk powder. The residual of neonicotinoid insecticides and their metabolites in samples were exacted by acetonitrile and extraction kits. The quantitative detection was performed by LC–MS/MS with multiple reaction monitoring (MRM) modes under positive ion electrospray ionization (ESI + ). The isotope dilution internal standard or external standard method was used for quantitation. The limits of quantification (LOQs, S/N = 10) were 2 μg/kg (IMI, IMI-U, ACE, IM 2–1, DIN-UF, THIA, and TMX) and 5 μg/kg (IMI-O, DIN, CLO, and FLU) for milk; 2 μg/kg (ACE), 15 μg/kg (THIA, IM 2–1, DIN-UF, THIA, and TMX), and 40 μg/kg (IMI-U, IMI-O, DIN, CLO, and FLU) for infant formula milk powder. At three spiked levels of 5 μg/kg, 10 μg/kg, 50 μg/kg (milk), or 40 μg/kg, 80 μg/kg, 400 μg/kg (infant formula milk powder), the recoveries were in the range of 71.7–108.7% and 71.9–107.1%; the relative standard deviations were below 12.6% and 13.9%, respectively. This method was simple, rapid, and accurate to determine the neonicotinoids and their metabolites residues in milk and infant formula milk powder.