Application of QuEChERS-based purification coupled with isotope dilution gas chromatography-mass spectrometry method for the determination of N-nitrosamines in soy sauce
A sensitive and rapid method involving an improved approach called the quick, easy, cheap, effective, rugged, and safe (QuEChERS) purification method and isotope dilution gas chromatography-mass spectrometry (GC-MS) was established to determine six N-nitrosamines (NAs) in soy sauce. Samples were firstly extracted by ethyl acetate. Then the extraction solution was concentrated by slow nitrogen gas blowing and subsequently purified using the QuEChERS-based purification method. Separation of six target NAs was performed on an INNOWAX polar capillary chromatographic column. All of the samples were detected by selected ion monitoring (SIM) mode of GC-MS and N-nitrosodimethylamine-d6 (NDMA-d6) and N-nitrosodipropylamine-d14 (NDPA-d14) were used as internal standards. The developed method was validated in terms of the linearity, limit of detection (LOD), matrix effects, specificity, accuracy and precision. Results indicated that this method is of good specificity with almost negligible matrix effects. Linear relations of six NAs were favourable in the range of 2.0–200 μg L−1 and the correlation coefficients were greater than 0.9994. The LODs were lower than 1 μg kg−1 (0.4–0.9 μg kg−1) and the limits of quantitation (LOQs) of the method were within the range of 1.2–3.0 μg kg−1. The mean recoveries for negative light and dark soy sauce samples at three spiked concentration levels were in the range of 80.2–112% with overall relative standard deviation (RSD) values (n = 6) of 2.5–6.8%. The validated method was simple and rapid, with good repeatability, and was successfully applied to determine the concentrations of NAs in soy sauce.