Based On MOFs Pore Screening And Selective Enrichment To Establish Detection Method Of Organophosphorus Pesticides And Phytohormone In Citrus Fruits

In recent years,in order to pursue the yield and quality of agricultural products,fruit farmers often spray pesticides to improve the quality of fruits.The accumulation of pesticides and phytohormones in fruits has a certain impact on human health,resulting in more and more serious food safety problems.Strengthening the effective monitoring and supervision of toxic and harmful substances in food is of great significance to ensure food safety and consumers’health.However,how to effectively eliminate matrix interference and detect pesticides and phytohormones sensitively is still a major challenge due to matrix interference in food.In recent years,metal-organic frameworks have been used in the field of analytical detection due to their large specific surface area,adjustable porosity,and rich functional groups.In this paper,a new method for the detection of pesticides and phytohormones in citrus fruits was constructed based on metal-organic framework,using dispersive solid phase extraction method combined with gas/liquid chromatography-triple quadrupole mass spectrometry.The adsorption mechanism was preliminarily discussed by infrared spectra and ultraviolet spectra.The experiment has achieved good results and the main research results are as follows:1.MIL-125-NH₂ was synthesized by solvothermal method,and a series of characterizations were carried out to prove its successful synthesis,including X-ray diffraction,Fourier transform infrared spectra,nitrogen adsorption-desorption isotherms and scanning electron microscopy.The metal-organic framework MIL-125-NH₂ was chosen as adsorbent to investigate its effect on the extraction of target and exclusion of impurities in pomelo.The extract was determined by gas chromatography-triple quadrupole mass spectrometry（GC-MS/MS）.A simple,environmentally friendly and reliable method for the determination of methyl 1-naphthaleneacetate（MENA）,parathion-methyl,fenitrothion,bromophos and phenthoate residues in pomelo was established.The key parameters of sample pretreatment were optimized by single factor experiment.Under the optimized conditions,a good matrix standard curve was obtained,the linear correlation coefficient R²>0.9922,the recovery of the target was64.7-116.8%,the LODs and LOQs were 0.03-1.07 ng/g and 0.11-3.57 ng/g,which was lower than the national maximum residue limit.The intra-day precision and inter-day precision were 1.3-8.9%and 3.8-14.9%,respectively.This method was successfully applied to the detection of pesticide residues in pomelo from five different producing areas.In addition,the adsorbent MIL-125-NH₂ can be reused at least 8 times,which saves the detection cost and is an efficient and economical method.The results show that the established method is effective and reliable.2.Based on the dispersive solid-phase extraction（d-SPE）method,a new detection method with microporous UiO-66 as adsorbent was established.Using high performance liquid chromatography-triple quadrupole mass spectrometry（HPLC-MS/MS）analysis technology,a new,efficient and sensitive method was established to detect 6-BA,ABA,IAA,IPA and IBA in Gannan navel orange.UiO-66 was synthesized by solvothermal method,and then characterized by X-ray diffraction,Fourier transform infrared spectroscopy,nitrogen sorption-desorption isotherm and scanning electron microscopy.In the sample pretreatment process,UiO-66 was directly used to separate and enrich phytohormones in the crude extract of Gannan navel orange,without further purification steps and simplifying the sample pretreatment process.Moreover,UiO-66 can exclude most of the matrix interferences by size sieving.The sample extraction parameters were optimized by orthogonal experiment,and other parameters were optimized by single factor experiment.Under the optimized conditions,the recoveries of the targets were 60.6-103.0%.The matrix standard working curve had good linearity,and the linear correlation coefficient was greater than0.9986.The range of LODs was 0.04-4.46 ng/g,and the range of LOQs was 0.14-14.86ng/g.The intra-day precision and inter-day precision were 1.09-6.00%and 3.93-21.61%,respectively.The parameters of the established method meet the experimental requirements and are used to detect the content of phytohormones in Gannan navel orange,which proves the effectiveness,reliability and stability of the method.3.The powder UiO-66 was coated on 7 mm glass beads by PDMS to synthesize shaped UiO-66 with by sol-gel technology.The shaped UiO-66-PDMS was directly put into the sample as adsorbent.The phytohormones in citrus fruits were extracted by UiO-66-PDMS.The target was detected by HPLC-MS/MS.A new method for the determination of forchlorfenuron,paclobutrazol and uniconazole in citrus fruits was established.In addition,the adsorption mechanism was preliminarily discussed by infrared spectra and ultraviolet spectra.The experimental results show that the adsorbent can exclude macromolecular interfering substances in the matrix while adsorbing the target.The linear range of the matrix standard curve of the target was0.9995-0.9998,the LOD was 0.09-0.17 ng/g,the recovery was 80.7-97.1%,and the intra-day precision and inter-day precision were 1.5-6.3%and 4.6-11.7%,respectively.The established method was applied to detect phytohormones in 10 citrus fruits,and the results were good.UiO-66 may adsorb the targets through hydrogen bonding andπ-πstacking.Compared with the traditional metal-organic framework powder,UiO-66-PDMS can be directly removed by a tweezer to achieve rapid separation,simplifying the sample pretreatment process,and avoiding the influence of metal-organic framework material residues on sample pretreatment and injection needle.