Simultaneous Determination of Neonicotinoid Insecticides and Their Metabolites in Honey by High Performance Liquid Chromatography-Tandem Mass Spectrometry with Dispersive Solid-Phase Extraction

The honey sample (2.00 g) was added into in a centrifuge tube with a cover, and 100 μL of isotope internal standard solution (200 μg·L^-1) and 10 mL water were added. After mixing well by vortex, the mixture was made up to 20 mL with methanol, and mixed well, centrifuged at 8 500 r·min^-1 for 5 min. 0.50 mL of the supernatant was taken and diluted to 10.0 mL with methanol, and the mixture was mixed well by vortex, then centrifuged at 8 500 r·min^-1 for 5 min. 1.0 mL of the supernatant was transferred into a centrifuge tube containing a homogeneously mixed adsorbent (30 mg of N-propyl ethylenediamine, 15 mg of C₁₈ powder and 50 mg of anhydrous MgSO₄). After vortexing and mixing for adsorption purification, the tube was centrifuged at 8 500 r·min^-1 for 5 min. All the supernatant was blowed to near dryness using nitrogen at 40 ℃, and the residue was disolved and made up to 1.0 mL with a mixture of methanol and 0.15% (volume fraction) formic acid solution (1+9). The solution was passed through a 0.22 μm filter, and the filtrate was analyzed by liquid chromatography-tandem mass spectrometry. Chromatographic separation was carried out using an Agilent Eclipse XDB-C₁₈ column, with a mixture in varying proportions of 0.15% formic acid solution containing 5 mmol·L^-1 ammonium acetate and methanol as mobile phase for gradient elution. Electrospray ion source, positive ion scanning mode and multireaction monitoring mode were used in the mass spectrometry, and the isotope dilution internal standard method and external standard method were used for quantification. The mass concentration of pyridoxine, dinotefuran, nitenpyram, thiame-thoxam, flonicamid, imidacloprid, clothianidin, chlorothiazide, acetamiprid, thiacloprid, 4-(trifluoromethyl)nicotinamide and N-desmethylpyrazole, was linear within definite ranges, and the lower limits of determination (10S/N) were between 2.5-12.5 μg·kg^-1. Tests for recovery was made by standard addition method to blank honey samples, giving results in the range of 79.9%-108%, and RSDs (n=6) were between 1.7% and 15%.