Determination of Azoxystrobin Residue in Strawberries by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

The sample (10.00 g) was added into 20.00 mL of acetonitrile, and the mixture was homogenized for 2 min at a high speed, and filtered with a filter paper. The filtrate was collected into a 100 mL cylinder containing 5 g of sodium chloride, and the cylinder was covered with a stopper and shaked vigorously for 2 min. After standing for 30 min, 10.00 mL of the supernatant was taken and purified with a Carbon/NH₂ solid phase extraction cartridge, which had been pre-rinsed with 5 mL of acetonitrile-toluene (3+1) mixture. The eluent was collected, and the cartridge was eluted with 20 mL of acetonitrile-toluene (3+1) mixture in 4 portions. The eluent was combined and evaporated to near dryness in a water bath at 40℃. The residue was made up to a volume of 5.00 mL with methanol (1+1) solution, and then the solution was vortexed well and then passed through a 0.22 μm filter membrane. The filtrate was separated on a Waters XBridge C₁₈ column (3.0 mm×50 mm, 3.5 μm), with methanol, acetonitrile and 0.1% (volume fraction) formic acid as mobile phase for gradient elution. Electrospray positive ion source and multiple reaction monitoring mode were used for mass spectrometry analysis. External standard method was used for quantification. Linear relationship between values of the quantitative ion peak area and the mass concentration of azoxystrobin was obtained in the range of 0.001-0.10 mg·L^-1, with the detection limit (3S/N) of 0.10 μg·kg^-1. The proposed method was applied to determination of azoxystrobin residues in strawberries, giving values of recovery obtained by standard addition method in the range of 78.0%-95.2%, and RSDs (n=6) less than 7.0%.