Research On Detection Method Of N-nitrosamines Based On Molybdenum Disulfide And Molecular Imprinting Polymers

N-nitrosamines are a group of organic compounds containing nitroso,which are strongly carcinogenic.In recent years,they have been frequently detected in environmental waters and food matrices,causing a serious threat to consumer health.For N-nitrosamines,existing pretreatment methods(e.g.,distillation and liquid-liquid extraction)have high consumption of organic reagents and serious matrix interference,and cannot effectively extract N-nitrosamines from matrices,making it difficult to achieve highly sensitive and efficient detection of these substances.Solid phase extraction techniques are widely used for enriching and extracting trace substances due to their low reagent consumption,high extraction speed and ease of operation,and the nanomaterials used determine the performance of the extraction process.To solve the detection problems faced by N-nitrosamines,in this experiment,molybdenum disulfide nanomaterials were prepared firstly and used as sorbents for the rapid extraction of N-nitrosamines from environmental water samples using their large specific surface area and large number of sorbent sites,and a method for detecting N-nitrosamines in environmental water samples was developed using liquid chromatography tandem mass spectrometry.Subsequently,molecularly imprinted polymers were prepared for complex food matrices and used as solid phase extraction sorbents for enriching and detecting N-nitrosamines in meat products,using their selective sorption capacity.The main findings were as follows.(1)A method was developed for the liquid chromatography tandem mass spectrometry instrumentation of four N-nitrosamines.The mass spectrometric conditions were optimized by setting the ionization injection voltage at 5500 V,the collision gas pressure at 8 psi,the ion source gas pressure at 30 psi for ion source 1,the ion source gas pressure at 30 psi for ion source 2,the ion source temperature at 550°C and the gas curtain gas pressure at 30 psi.The mass spectral information(parent ions,daughter ions)of four N-nitrosamines was determined by positive ion scanning in multiple reaction monitoring mode,and the liquid chromatographic conditions were optimized for the separation of the four substances using a C18 column.The mobile phase consisted of 0.05%FA-water solution(A)and methanol(B)at a flow rate of 0.3m L/min.The injection volume was 10?L.The gradient program was as follows:0-2min,kept at 10%B;2-6 min,from 10%B to 90%B;6-9 min,kept at 90%B;9-10 min,from 90%B to 10%B;10-12 min,kept at 10%B.(2)The flower-like molybdenum disulfide materials were prepared by hydrothermal method,characterized as three-dimensional flower-like microspheres of approximately 500 nm in diameter,used as sorbents in solid-phase extraction process for enriching N-nitrosamines.The effects of sample volumes,washing solvents and elution solvents on the extraction efficiency of the N-nitrosamines were investigated.A method based on molybdenum disulfide-solid-phase extraction and high-performance liquid chromatography-tandem mass spectrometry was developed for enriching N-nitrosamines in environmental water samples under optimal conditions(50 m L sample volume,p H 7,2 m L H₂O eluent and 3 m L 0.05%ammonia-methanol eluent).The linearity of four N-nitrosamines was good in the range of 1-100 ng/m L with R~2 greater than 0.9900.The recoveries from 68.9%to 106.1%at three different spiked levels(2,5 and 8 ng/m L)with RSDs of 0.46%to 7.17%.The developed method was highly sensitive and simple in operation.It also introduces a new solid phase extractant for enriching N-nitrosamines in environmental water samples.(3)Dummy template imprinting polymers were prepared by precipitation polymerization using dibenzyl alcohol,5-nonanol and 1-carboxypyrrolidine as dummy template molecules and methacrylic acid as functional monomer.By characterization,the results show that the imprinted polymers were clearly micro-spherical with a diameter around 500 nm and the non-imprinted polymers were irregularly connected in blocks.The sorption performance of the polymeric materials was evaluated by static and dynamic sorption experiments and Scatchard's equation,the adsorption of imprinted polymers(7270?g/g)was significantly higher than non-imprinted polymers(5460?g/g).The solid phase extraction conditions were optimized.under the optimal conditions(H₂O as the loading solvents,p H 7,2 m L of H₂O as the elution solvents and5 m L of methanol as the desorption condition),the method based on molecularly imprinted polymers for enriching and detecting four N-nitrosamines in meat products by solid phase extraction coupled with high performance liquid chromatography tandem mass spectrometry was developed.The results showed that the four N-nitrosamines exhibited good linearity in the range of 1-500 ng/m L with R~2 between0.9990 and 0.9997.The recoveries of four N-nitrosamines were ranged from 61.0%to105.2%at three spiked levels(5,10 and 20 ng/m L),RSD values were between 1.2%and 9.76%.The developed method has the advantages of high sensitivity and good selectivity,providing a new specific identification adsorbent for enriching N-nitrosamines in complex meat products.