| “Food is the priority for the people,and food security is the priority”.The frequent occurrence of food safety problems caused by chemical pollution has posed a serious threat to human health.From the perspective of three major technical problems-“complicated matrix effect”,“trace level”and“environmentally unfriendly”-caused by chemical pollutants including polybrominated diphenyl ethers(PBDEs)or herbicides in food and environment,there is an urgent need to choose appropriate sample pretreatment technologies and construct functionalized adsorbents that could perform the dual functions of purifying the matrix in the sample and enriching the target pollutants with high selectivity.Therefore,the advantages of high sensitivity,high selectivity,rapidity and environmental protection of established methods are realized.Covalent organic framework(COF)and microporous organic framework(MON)materials possess superior controllable topology and pore size,functional modification,high specific surface area,and high stability,endowing them with great potential in sample pretreatment technology.In this paper,from the perspective of structural characteristics of polybrominated diphenyl ethers,phenoxycarboxylic acid herbicides,triazine herbicides and phenylurea herbicides,based on density functional theory(DFT)and strong weak interactions including halogen bond,ionic bond,and hydrogen bond,we described the construction of four functionalized COF or MON materials.Combined with sample pretreatment methods and chromatography–mass spectrometry detection technology,four highly sensitive and rapid samples pretreatment methods for analyzing the chemical contaminant residues in food and environmental samples were established.The main results are as follows:1.Reticulated triazine-cored COF for ultrasensitive detection of PBDEs emitted from water and food samples by d SPE-GC-MS/MS:Experimental and DFT studyA novel reticulated TAPT-DMTA-COF with N/O functional groups(i.e.,imine linkage,triazine,and methoxy)has been successfully synthesized based on PBDEs with multiple?-hole electron–withdrawing groups(halogen atom,Br).After screening three different synthesis conditions(e.g.,solvent,catalyst concentration and reaction temperature),this resultant presented a large surface area of 1734 m~2·g-1,high crystallinity,and exceptional stabilities.DFT and independent gradient model(IGM)analysis on adsorption mechanism revealed that in all adsorption configurations of complexes,halogen-bonding was observed to play a pivotal role than?-?,C-H···?interactions.Furthermore,the positive linear relation between calculated adsorption energy and Br content directly clarified that enrichment behavior of PBDEs can be attributed to halogen-bonding.In case of PBDE analysis,combined with gas chromatograohy-mass spectrometry(GC-MS/MS),this approach achieved excellent results with wide linearity(0.1-5000 ng·L-1),low limits of detection(0.03-0.13 ng L–1)and high spiked recovery rates(71.8-118.5%).Finally,the promising potential applications of aforementioned method were verified by spiking water,fish,and milk samples with PBDEs;good PBDEs recoveries were obtained.In this study,the DFT and IGM analysis will help in elucidating the multiple adsorption behaviors between COFs and PBDEs and offer important strategy for precisely designing COFs for effective enrichment of contaminants.Additionally,it can serve as an essential technical foundation for risk assessment of environmental and argo-food safety issues.2.Cationic covalent organic nanosheets for rapid and effective detection of phenoxy carboxylic acid herbicides residue emitted from water and rice samples by d SPE-LC-MS/MS:Experimental and DFT studyAccording to the formula of monobasic weak acid distribution fraction,theoretically,at p H?4,phenoxy carboxylic acid(PCAs)primarily exist in the anionic form.On the basis of the ionic bond of electrostatic interaction,a cationic TpTGCl was constructed.By selecting the2-Methyl-4-chlorophenoxyacetic acid(MPCA)system as an example,binding energy of the MCPA@TpTGCl system was calculated.The analysis of binding affinity by DFT and IGM analysis demonstrated that PCAs bonded to TpTGClprimarily via electrostatic attraction,N-H···O and O-H···O bonds,and C-H···?interactions.High calculated binding energy of-211.8091 kcal·mol-1 revealed that theoretically TpTGCl can achieve fast,highly sensitive and high-capacity adsorption for PCAs.Through investigating synthesis conditions,TpTGCl with a crystalline form was synthesized using a simple synthetic condition.The Langmuir and Freundlich adsorption isotherm showed that the adsorption of PCAs on TpTGCl was a favorable adsorption process and the amount of adsorbed was as high as 111.6-178.6 mg·g-1.Combined with liquid chromatography-mass spectrometry(LC-MS/MS),a rapid and highly sensitive analytical method for determining PCAs in water and rice matrix was established.For water matrix samples,the five PCAs have a good linear relationship in the range of 3-625ng·L-1,with the correlation coefficient ranging from 0.9919 to 0.9967,and the limit of detection was 0.43-0.78 ng·L-1.Additionally,for rice matrix samples,the five PCAs have good linear relationship in the range of 0.125-25 ng·g-1,with the correlation coefficient ranging from 0.9945 to 0.9988,and the limit of detection was 0.016-0.036 ng·g-1.The matrix effect of PCAs in rice ranged from-1.9 to 9.9%.The recoveries of PCAs in spiked water and rice samples ranged from 74.4-109.6%and 75.3-108.8%,respectively.This study provides an idea for designing functionalized COF materials for capturing ionic target compounds.3.Hydroxyl group–enriched microporous organic network for ultrasensitive solid-phase extraction of triazine herbicides emitted from water and fruit samples by SPE-LC-MS/MS:Experiment and DFT calculationWe fabricated a new hydroxylated microporous organic network(OH-MON)with a permanent micropore of 1.86 nm,high surface area,and high chemical and thermal stability,synthesized by simple Sonogashira-Hagihara polymerization.When utilized as an advanced solid-phase extraction(SPE)adsorbent for efficient adsorption of triazine herbicides,desirable linear correlations with 0.05-250 ng·L-1,an ultra-low detection limit of 0.03-0.21ng?L-1 and good precision for triazine herbicides were achieved.The matrix effect values of triazine herbicides in fruit juice ranged from-6.5%to 1.8%,indicating that the matrix in fruit samples does not affect triazine herbicides.Our proposed approach showed some merits of broader matrix applicability,lower dosage,lower LODs,higher loading volume,and higher enrichment factor than other reported approaches.Compared with the commercial SPE cartridges,the self-made OH-MON cartridge owned the least amount of adsorbent,a longer service life and a lower cost.A preliminary practical application of the developed method was proved by the efficient detection of triazine herbicides in water and fruit samples with good recoveries(72.8%-100.4%and 72.0%-97.7%for water and juice samples,respectively).All six triazine herbicides were detected in unspiked water samples.Compared to?-?interactions,-OH···N-and-NH···O-hydrogen bonds dominate the adsorption of OH-MON with triazine herbicides,as demonstrated by the theoretical calculation and selectivity test.This study combines high sensitivity,high reproducibility,high stability and commerciality,and it is suitable for the preconcentration and detection of triazine herbicides in complicated samples.4.Room-temperature synthesis of covalently linked magnetic microporous organic network for ultrasensitive enrichment of phenylurea herbicides emitted from water samples by MSPE-LC-MS/MS:Experiment and mechanism studyA facile strategy for the fabrication of novel sea urchin-like structure magnetic porous nanocomposite via grafting a rod-like MON material onto the surface-modified NH2-Fe3O4hydrophilic magnetic was prepared by a room temperature synthesis method.The OH-COOH-MON synthesis monomers were screened,and the synthesis methods of NH2-Fe3O4 and Fe3O4@OH-COOH-MON were optimized.It possesses good hydrophilicity,supermagnetism,high specific surface area,making it an ideal adsorbent for magnetic solid-phase extraction(MSPE)for concentrating and monitoring phenylurea herbicides(PUHs).According to the systematic studies,a set of specific experimental factors(i.e.,adsorbent material:3 mg;adsorption and desorption time:2 min)would be beneficial producing the maximum adsorption levels,suggesting that functionalized OH and COOH,hydrophilic and the morphology play a positive role in the enrichment process for PUHs.The Fe3O4@OH-COOH-MON-based MSPE-LC-MS/MS method afforded a good linear relationship in the concentration range of 1-750 ng·L-1 with linear correlation coefficient of above 0.9911,low limits of detection(0.03-0.22 ng·L-1),and low limits of quantification(0.10-0.72 ng·L-1).In order to assess the practicability of the proposed MSPE quantitative method for the detection of PUHs,the spiked recovery experiments were performed.The recoveries of the six PUHs were between 71.0-110.6%.DFT calculation indicated that,theoretically,hydrogen-bonding,halogen-bonding,and?-?stacking lead to the favorable affinity to PUHs.Furthermore,X-ray photoelectron spectroscopy(XPS)experiment verified the existence of?-?stacking and hydrogen-bonding in real environment.Selectivity experiments not only uncovered the minor role of hydrophobicity in enrichment process,but also confirmed that Fe3O4@OH-COOH-MON could serve as a superior sorbent for analyzing the compounds with hydrogen and halogen bonding sites.This study provides a synthetic concept for the construction of hydrophilic covalent magnetic MON materials and a method for elaborating the enrichment mechanism in theory and in real environment. |
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