Abstract: [Objective] To establish an analytical method for determining the content of aflatoxin B₁ in cheese and milk using isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS). [Method] After sample extraction,it was purified using an immunoprecipitation column,then concentrated by nitrogen evaporation. The content of aflatoxin B₁ was subsequently determined by LC-MS/MS after re-dissolution with the initial mobile phase. [Result] The separation effect of the target analyte was good,and the analytical method was rapid and simple. Within the concentration range of 1 to 80 ng/mL,the samples were analyzed by sequentially injecting concentration standard solutions. The linear regression was performed using the ratio of the chromatographic peak area of aflatoxin B₁ to that of each corresponding internal standard as the ordinate and the concentration as the abscissa. The standard curve equation obtained was：Y=0.631 69-3.151 51×10^-4X,with a linear correlation coefficient（R²）of 0.999 82. The detection limit of aflatoxin B₁ in cheese samples was 0.02 μg/kg,and the quantification limit was 0.05 μg/kg,and the recovery rate ranged with spiked samples was 74.59% to 90.52%;the detection limit of aflatoxin B₁ in milk was 0.02 µg/kg,and the quantitative limit was 0.1 µg/kg,and the recovery rate with spiked samples was 79.85% to 100.63%. [Conclusion] This method had high accuracy,fast detection speed and excellent separation performance,and is suitable for quantitative analysis of aflatoxin B₁ content in cheese and milk samples.

Key words: aflatoxin B₁, dairy products, liquid chromatography-tandem mass spectrometry（LC-MS/MS）