Analysis Of Strobilurin Fungicides By Liquid Chromatography Tandem Mass Spectrometry Based On Molecularly Imprinted Hybrid Materials

Strobilurin fungicides are a class of broad-spectrum fungicides used for the prevention and control of fungal diseases in crops and have been widely used in crop production.The large and unscientific use of these fungicides can lead to residues in agricultural products,which can cause a series of safety hazards to human health（diarrhea,teratogenic,carcinogenic,etc.）.Chromatography-mass spectrometry techniques are often used to detect fungicide residues,but due to the complexity of the agricultural matrix and the presence of substances often at trace levels,effective sample pretreatment is a necessary process prior to instrumental detection.The aim of this study was to prepare molecularly imprinted hybrid materials with high adsorption and high recognition capacity.Magnetic imprinted polymers and metal-organic frameworks@molecularly imprinted hybrid complexes were prepared by surface imprinting techniques,respectively,and a（magnetic）solid-phase extraction-high performance liquid chromatography tandem mass spectrometry method was developed for the enrichment and detection of multiple strobilurin fungicides in agricultural products.The details of the study and the results are as follows:（1）Magnetic molecularly imprinted polymers（MMIPs）were obtained by surface imprinting technique,using pyrimethanil as a template molecule and polymerizing a molecularly imprinted layer on the surface of magnetic nanoparticles.The structure was characterized by scanning electron microscopy,transmission electron microscopy,fourier transform infrared spectroscopy,and magnetic intensity vibrometry,which showed that the material has a distinct core-shell structure（imprinted shell of approximately 50～150 nm）and good magnetic separation properties(saturation magnetisation value of 6.3 emu g^-1).The adsorption performance was evaluated by dynamic and static adsorption experiments,which showed that the material has high efficiency adsorption performance（adsorption time of 3 min）and large adsorption(Q_max=137.4 mg g^-1).The MMIPs were used in magnetic solid phase adsorption experiments.The MMIPs were used in the magnetic solid phase extraction process to optimize a series of MSPE conditions.Under the optimal conditions（4 m L sample matrix,20%ACN-H₂O as sample solvent,p H=6,adsorption time of 5 min,and Me OH as elution solvent）,an MSPE-HPLC-MS/MS method was developed for the enrichment and detection of six strobilurin fungicides in different agricultural products.The results showed that the method has good linearity（R²≥0.9990）with the limits of detection of 0.03～0.49 ng g^-1 and the limits of quantification of 0.09～1.64 ng g^-1.The recoveries of the six fungicides in different agricultural products（winter jujube,pear,zucchini and cucumber）at three spiked levels of 20,50 and 100 ng g^-1 ranged from 71.5%to 115.8%,The RSDs ranged from 0.3%to 8.3%.This study not only produced imprinted hybrid materials with specific recognition and high adsorption capacity for strobilurin fungicides,but also established an MSPE-HPLC-MS/MS method with proven ease of operation and high sensitivity,which provides a reference for the detection of trace strobilurin fungicides in agricultural matrices.（2）A novel molecularly imprinted hybrid material with a core-shell structure（ZIF-8@MIPs）was prepared by surface imprinting technique using a metal-organic framework as the core.The structure of the material was analyzed by a series of characterization tools,which showed that the molecularly imprinted layers（about 20 nm）were successfully polymerized on the surface of the metal-organic framework in a typical core-shell structure.The dynamic-static adsorption experiments showed that the prepared hybrid material has a large adsorption capacity(102.5 mg g^-1)and a fast adsorption capacity（only 5 min）.An SPE-HPLC-MS/MS method based on ZIF-8@MIPs was developed for the detection of six strobilurin fungicides in different agricultural products under optimal conditions（p H=7,20%ACN-H₂O on sample;1 m L H₂O as washing solvent;2 m L ACN as elution solvent）.The method showed good linearity in the range of 5～200 ng m L^-1 with R² greater than 0.9990.Good recoveries（83.5%to 129.0%）were obtained at three different levels in the agricultural products（apple,pear,banana,cabbage,cabbage and cucumber）with RSDs of 0.5%to10.2%.The limits of detection and limits of quantification were 0.01～1.12 ng g^-1 and0.03～3.73 ng g^-1,respectively.These results indicate that ZIF-8@MIPs have good potential for the enrichment and separation of trace strobilurin fungicides in different agricultural products,and the established method has the advantages of high sensitivity and good selectivity.