Determination of 12 Nitrosamines Residues in Milk by Emulsification/Demulsification Method Coupled with Gas Chromatography Tandem Mass Spectrometry

Based on the emulsification/demulsification method, a gas chromatography tandem mass spectrometry method was established for the quantitative determination of 12 nitrosamines in milk. The optimization results of pretreatment conditions such as the type of filter membrane, the type of extractant and the number of extractions were as follows: The type of filter membrane was nylon, the extractant was acetonitrile, and the number of extractions was two times. After acetonitrile extraction, deproteinizing, and degreased by emulsification/demulsification, the samples were separated on the HP-INNOWAX chromatographic column. The content of nitrosamines was quantitatively determined by the internal standard method, using multi-reactive ion monitoring (MRM) mode. The results showed that the linear range of N-nitrosopyrrolidine (NPYR) was 2~100 ng/mL, and the linear range of the other nitrosamines was 1~100 ng/mL. All nitrosamines had good determination coefficient which was greater than 0.995. During the high, medium and low-level fortification experiments, the recovery rate ranged from 90.90% to 114.30%, the intra-day precision ranged from 1.76% to 7.62%, and the inter-day precision ranged from 2.75% to 7.71%. The limit of quantitation (LOQ) of N-nitrosopyrrolidine (NPYR) was 4 µg/kg, and the LOQ of other compounds was 2 µg/kg. The method was precise and accurate, that met the demand of accurately testing 12 nitrosamines in milk. The test results of the actual samples indicated that N-nitrosodiphenylamine (NDPhA) was detected in six milk samples, and the content ranged from 4.29 to 6.67 μg/kg.