Determination of 4 Kinds of Aflatoxin in Tea by Liquid Chromatography-Tandem Mass Spectrometry

The sample (5.000 0 g) was ultrasonically extracted with 20 mL of acetonitrile for 20 min. After centrifugation, 4 mL of the extract was directly purified through the Prime HLB solid phase extraction column, the purified solution was collected. Then the column was eluted with 2 mL acetonitrile in 2 portions, and the purified solution was combined, concentrated to about 4 mL by nitrogen blowing, diluted to 50 mL with phosphate buffer solution (pH 7.4). The solution was passed through the immunoaffinity column and the column was rinsed with 20 mL of water and finally eluted with 4 mL of acetonitrile in 2 portions. The eluent was collected and concentrated to nearly dry by nitrogen blowing. The residue was dissolved and diluted to 1 mL with methanol-water (50+50), and the solution was filtrated with 0.45 μm organic phase filter. The filtrate was separated on a VP-ODS C₁₈ column (150 mm×2.0 mm, 4.6 μm), with acetonitrile and 0.1% (φ) aqueous formic acid (containing 0.01 mol·L^-1 ammonium acetate) as the mobile phase for gradient elution. Electrospray positive ion sources and multiple reaction monitoring mode were used for mass spectrometry analysis. Linear relationships were found between peak areas and mass concentrations of aflatoxin B₁, B₂, G₁, G₂ in the same range of 0.06-5.0 μg·L^-1, with the same detection limit (3S/N) of 0.02 μg·kg^-1. Values of recovery obtained by standard addition method were 81.5%-89.6%, and the relative standard deviations (n=6) of the measured values were 3.6%-6.5%.