Determination of Nine N-Nitrosamines in Animal Food by Gas Chromatography-Tandem Mass Spectrometry

10.00 g of the sample was taken, then 100 μL of mixed internal standard solution (1.00 mg·L^-1, composed of N-nitrosodimethylamine-d6 and N-nitrosodi-n-propylamine-d14) and 20 mL of acetonitrile were added. After vortexing for 1 min, the mixture was freezed at -20℃ for 20 min. Then extract salt (4 g of magnesium sulfate, 1 g of sodium chloride) was added, and the mixture was oscillated rapidly for 30 s, centrifuged at 8 000 r·min^-1 for 10 min at 0℃. The supernatant was taken and 10 mL of acetonitrile saturated n-hexane was added, and the mixture was vortexed for 1 min, centrifuged at 6 000 r·min^-1 for 3 min at 0℃. The n-hexane layer was removed, and purification packing material (50 mg of N-propyl ethylenediamine, 150 mg of blocked octadecyl boned silica gel, 900 mg of sodium sulfate) was added. After vortexing for 1 min and centrifuging at 8 000 r·min^-1 for 5 min at 0℃, the supernatant was concentrated by nitrogen blowing (not dry), and made up to 1.0 mL with acetonitrile. Nine N-nitrosamine compounds were determined by gas chromatography-tandem mass spectrometry. The VF-WAXms column (0.25 mm×30 m, 0.25 μm) was selected for chromatographic analysis. Electron impact ion source and multiple reaction monitoring mode were selected in mass spectrometry. Linear relationships were found between peak area and mass concentration of the nine N-nitrosamine compounds in the range of 5.0-150 μg·L^-1. The detection limits were 0.1 μg·kg^-1, and the lower limits of determination were 0.5 μg·kg^-1. Recovery obtained by standard addition method ranged from 89.0% to 117%, and the relative standard deviations (n=6) of the measured values ranged from 0.6% to 8.0%.