Determination of 24 Polycyclic Aromatic Hydrocarbons in Infant Formula by Gas Chromatography-Triple Quadruple Mass Spectrometry

The mixed internal standard solution, water and aqueous ammonia were mixed with the sample, and the mixture was heated in the water bath at 65℃ for 10 min. Anhydrous ethanol, anhydrous diethyl ether and petroleum ether were added for extraction. After vibration and centrifugation, the upper organic phase was taken and blown to dryness by nitrogen at 45℃. Ethanol solution containing potassium hydroxide was added, and the mixture was saponified at 70℃ for 3 min. Water and n-hexane were added, and the solution was vortexed and centrifuged, n-hexane phase of which was taken and passed through EU polycyclic aromtic hydrocarbons (PAHs) solid phase extraction column activated at the flow rate around 1.0 mL·min^-1. The above column was rinsed with n-hexane, and eluted with the mixed solution of dichloromethane and ethyl acetate at volume ratio of 1:1. The eluent was collected and blown to dryness by nitrogen at 40℃. The residue was redissolved by the mixed solution of acetone and isooctane at volume ratio of 1:1, and the above solution was passed through a 0.22 μm filter membrane. The filtrate was introduced into the gas chromatograph, and separated on DB-EUPAH capillary column under programed temperature. Targets obtained was detected by multiple reaction monitoring mode in the tandem mass spectrometer, and quantified by internal standard method. It was shown that the mass concentrations of the 24 PAHs were linearly related with the ratios of the respective chromatographic peak area to the peak area of internal standard in the range of 0.244-15.6 μg·L^-1, with detection limits in the range of 0.008-0.200 μg·kg^-1. The spiked recoveries ranged from 72.0% to 128%, giving RSDs (n=6) of the determined values not more than 12%. The prescribed method was applied to the analysis of 11 commercial infant formulas, and the positive sample detection rate was 45.45%. The PAHs detected were chlorobenzene, benzoa anthracene, benzob fluoranthene and benzoa pyrene, while the other 20 PAHs were not detected, with the total amount (1.92 μg·kg^-1) of PAHs detected in one of stage 1 infant formula more than the limit (1.00 μg·kg^-1) stipulated by EC No 835/2011.