Determination of nine <italic>N</italic>-nitrosamines in animal derived foods by QuEChERS-isotope dilution combined with gas chromatography-tandem mass spectrometry

In this study, a comprehensive analytical method based on gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed for the determination of nine N-nitrosamines in animal derived foods. There are many kinds of N-nitrosamines in foods that are harmful to human health. However, the national standard GB 5009.26-2016 pertains only to the detection of N-dimethylnitrosamine; there are many drawbacks of this method, such as complicated sample preparation, low recovery rate, and poor reproducibility. Hence, it is of practical significance to establish a method for the simultaneous determination of a variety of N-nitrosamines. The optimal extraction conditions for the developed method were as follows: 10.0 g aliquots of the sample were placed in a 50 mL centrifuge tube, followed by the addition of 10 mL acetonitrile and 200 μL internal working standard solutions. After 30 min of freezing treatment, 4 g magnesium sulfate and 1 g sodium chloride were added for dehydration, and the tube was centrifuged at 9000 r/min for 5 min. After vortex centrifugation, 5 mL of the clear supernatant was purified using 150 mg polystyrene divinylbenzene (PLS-A). The purified extracts were dewatered using 1.6 g MgSO4 and 0.4 g NaCl, and then filtered through a 0.22 μm membrane filter unit prior to GC-MS/MS analysis. Temperature-programmed was applied at an initial temperature of 50 ℃. After 0.16 min, the temperature was raised to 220 ℃ at the rate of 900 ℃/min for 5 min. N-Nitrosamines were separated on an HP-Innowax column (30 m×0.25 mm×0.25 μm). Identification and quantification were achieved using an electron impact ion (EI) source in positive ion mode with multiple reaction monitoring (MRM). The internal standard method was used to quantify the N-nitrosamines. Under the optimal conditions, the correlation coefficients of the standard calibration curves were not less than 0.99 in the range of 0.1-50.0 μg/L. The limits of detection were 0.03-0.30 μg/kg (S/N=3), and limits of quantification were 0.15-1.00 μg/kg (S/N=10). At spiked levels of 0.5, 1.0, and 3.0 μg/kg, the average recoveries of N-nitrosamines in spiked samples ranged from 80.4% to 98.5%, with relative standard deviations between 2.41% and 12.50%. This method was used to determine animal derived food products, except N-itrosomethylethylamine and N-nitrosomorpholine, others were founded. The results showed that N-nitrosamines levels in salted aquatic products were generally higher than those of the other samples. The method established in this study is simple to operate, and it does not require any time-consuming distillation extraction. Furthermore, there is minimal consumption of samples and reagents; consequently, the experiment cost is reduced, and the method is environmentally friendly. This method has theoretical and practical significance for the control of N-nitrosamines residues in animal derived foods, establishment of detection standards, and corresponding management measures.