New Methods For The Highly Selective Analysis Of Bisphenol A And Aristolochic Acid Ⅰ In Food Based On Molecularly Imprinted Polymers

Food is the material foundation for the survival and development of human beings.However,the intervention of risk factors from different sources could have a certain impact on the safety of food quality.Bisphenol A(BPA)and aristolochic acid I(AAI)are two food risk factors that are highly concerned at present.Among them,BPA is a typical environmental endocrine disruptor,which can directly penetrate into food from food packaging materials,or through environmental media transmission and food chain enrichment,and finally enter the human body,causing homeostasis imbalance in the body and serious health hazards;Aristolochic acid compounds naturally exist in Aristolochia,Asarum and other plants,with the highest content of AAI,which has strong nephrotoxicity and carcinogenicity and is extremely harmful to human health.Aristolochia acid compounds are contained in the common food and drug dual-use plant Houttuynia cordata,while the free AAI in soil or water will also migrate to nearby crops,causing food contamination.Therefore,it is necessary to study and construct new methods for efficient analysis of the above two risk factors in food,and to effectively monitor them.Given the complexity of food substrates and the fact that BPA and AAI are generally low in food,how to effectively eliminate the interference of coexisting substances and meet the requirements of sensitive and accurate determination remain a huge challenge.Based on this,two risk factors,BPA and AAI,were selected as the research objects in this paper.According to their occurrence characteristics in food and structural features,a series of molecular imprinted polymers(MIPs)with different functions were developed by adopting the surface molecular imprinting technology and introducing the role of stimuli-responsive polymers or deep eutectic solvents(DESs)system,and the molecular imprinting technology was innovated and developed.The MIPs were used for specific separation and enrichment of BPA and AAI in food with different matrices.New methods for the highly selective analysis of BPA and AAI in food were established by coupling high performance liquid chromatography(HPLC)analysis technology,and were applied to the detection of actual food samples with satisfactory results.The main research results are as follows:1.A novel method for the highly selective analysis of BPA in beverages with different matrices based on hydrophilic MIPs was developed.Using BPA as the templates,N-isopropylacrylamide(NIPAM)as thermosensitive functional monomers and 2-(dimethylamino)ethyl methacrylate(DMAEMA)as pH responsive functional monomers,the polymerization was initiated on the surface of modified Fe3O4 magnetic microspheres to obtain hydrophilic MIPs with regular core-shell structures.Such MIPs had strong hydrophilicity,adsorption capacity of 8.97 mg/g,and good selectivity(the imprinting factor was 4.25,and the selectivity factors were within the range of 2.274.74).It could realize the controllable adsorption or release of BPA by regulating the environment temperature or pH value.The hydrophilic MIPs were used for selective separation and enrichment of BPA in beverages,and the target analyte was analyzed by HPLC.Under the optimized experimental conditions,the linearity of BPA was good within the concentration range of 0.015-10 μmol/L,the correlation coefficient(R2)reached 0.9996,and the limit of detection(LOD)was as low as 3.75 nmol/L.The recoveries of BPA in real samples at three spiked levels(0.1,1 and 4 μmol/L)were 83.4-96.3%.The relative standard deviations(RSDs)of intra-day repeatability(n=6)and inter-day repeatability(n=36)were less than 3.0%and 6.8%,respectively,indicating that the method was accurate and feasible.The method was applied to the sample analysis of mineral water,carbonated drink,fruit and vegetable juice,Red Bull energy drink,tea drink,coconut juice and lactobacillus drink,and good results were obtained.After six adsorption-desorption cycles,the adsorption efficiency of the hydrophilic MIPs was still above 86.5%,indicating that the MIPs were economical and practical.2.A new method for the efficient analysis of AAI in Houttuynia cordata based on thermosensitive MIPs was developed.On the basis of the previous studies,the thermosensitive MIPs were prepared through the surface molecular imprinting technology using modified magnetic graphene oxide as the carrier,AAI as the template molecules,NIPAM as the thermosensitive functional monomers,and methacrylic acid(MAA)as the functional co-monomers.The MIPs showed good affinity to AAI,with maximum adsorption capacity of 8.51 mg/g,and could reversibly capture or release AAI with the change of environment temperature.Compared with the traditional nonthermosensitive molecular imprinted materials which were directly eluted by organic solvent,the thermosensitive MIPs had shorter elution time and consumed less organic eluting solvent.The thermosensitive MIPs were used to specifically separate AAI from Houttuynia cordata,and the target analyte was analyzed by HPLC.Under the optimized experimental conditions,AAI had a good linear relationship within the range of 0.08-30 mg/L,and R2 was 0.9996.The LOD value was 26.67 μg/L.The results of spiked recovery ranged from 83.1 to 99.7%,and RSDs of inter-day(n=36)and intraday(n=6)were lower than 5.0%.The method was applied to the analysis of Houttuynia cordata samples from different habitats with good results.This method was rapid,sensitive and accurate,and could meet the requirements of green and efficient analysis of AAI in food with complex matrices.3.Based on the aforementioned research,a new strategy of stimuli-responsive molecular imprinting based on DESs system was innovatively proposed.First,NIPAM was used as the hydrogen bond donor,(3-acrylamidopropyl)trimethylammonium chloride(APTMAC)was used as the hydrogen bond acceptor,and they reacted at 80℃for 1h at a molar ratio of 1:1,so as to build a simple DESs system.AAI was selected as the templates,and the DESs system was used as a new thermosensitive functional monomer to initiate molecular imprinting polymerization on the surface of modified magnetic graphene oxide.The DESs-functionalized MIPs were prepared,and the properties were analyzed.The results showed that the maximum adsorption capacity of the MIPs was 11.84 mg/g within only 30 min.It can be seen that the DESs system introduced into the preparation of MIPs as functional monomers could significantly enhance the hydrogen bond interaction between the MIPs and the target molecules,and cooperate with specific recognition sites,showing superior adsorption capacity and rapid adsorption kinetics.The MIPs had high selectivity(the selectivity coefficients were within the range of 2.98-4.15,which were superior to those of the above thermosensitive MIPs),and could also efficiently elute the target molecules by regulating the ambient temperature.According to the molecular structure characteristics of AAI,two other compounds containing carboxylic acid groups,rhein(RH)and glycyrrhizic acid(GA),were selected as the templates.Under this new strategy mode,two new types of MIPs were synthesized.The feasibility of this new strategy of stimuli-responsive molecularly imprinting based on DESs system was verified through relevant characterization techniques.4.To explore the application effect of a new type of MIPs prepared under the new strategy of stimuli-responsive molecular imprinting based on the DESs system in the analysis of actual food samples,a new method for the highly selective analysis of AAI in Houttuynia cordata was constructed by using the DESs-functionalized MIPs as dispersive solid-phase extraction adsorbents coupled with HPLC technique.A good linearity was obtained for AAI within the concentration range of 0.1-40 mg/L,and R2 was 0.9952.The LOD and LOQ values of AAI were 28.57 μg/L and 95.23 μg/L,respectively.The inter-day(n=36)and intra-day(n=6)precisions of Houttuynia cordata samples at three spiked levels(0.5,2.0 and 5.0 mg/L)were less than 6.3%,and the recovery rates were 83.9-99.8%,indicating that this method was applicable to the analysis of AAI in Houttuynia cordata with complex matrices.Even after nine adsorption-desorption cycles,the recovery rate of the MIPs for the spiked Houttuynia cordata samples was still above 80.5%,showing that the material had good reusability.This study further expanded the application of MIPs in food safety analysis.