Determination Of Pesticide Residues In Fruits And Vegetables Using HPLC Coupled With Covalent Organic Frameworks-based Magnetic Solid-phase Extraction

In modern agriculture,fungicides and pesticides are widely used to protect crops.Because of their stability,mobility,and long-term effects on organisms,they are one of the most dangerous environmental pollutants.Pesticide residues in the environment,fruits and vegetables can enter the human body along the food chain,which seriously affects human health.At present,researches on the detection methods of pyrethroids,amide fungicides and phenylpyrazoles have attracted much attention.The main analytical methods involved include high performance liquid chromatography（HPLC）,gas chromatography-mass spectrometry（GC-MS）,and liquid chromatography-mass spectrometry（LC-MS）,and so on.For the detection of pesticide residues in environmental,fruit and vegetable samples,the sample matrix is usually complicated,and the level of pesticide residues is lower than the detection limit of many analytical methods.In order to reduce the interference of the matrix on the determination of pesticide residues and improve the detection sensitivity,sample pretreatment is a very effective method.There are many sample preparation techniques used in the literature to detect pesticide residues,such as solid-phase extraction,liquid-liquid extraction,solid-phase microextraction,and stirring rod adsorption extraction.However,these traditional technologies often require complicated operation steps and consume large amounts of organic solvents,which is harmful to the environment.In this study,we briefly introduce the research background of pesticide residues and review the hazards of pyrethroids,amide fungicides,phenylpyrazole insecticides,the characteristics of common detection methods and sample preparation techniques.In order to achieve rapid,simple,and efficient pre-enrichment and detection of trace pesticide residues in fruit and vegetable samples,we conducted the following studies:A novel magnetic solid-phase extraction adsorbent（Fe₃O₄-NH₂@TpPa-1）was synthesized by ultrasonic method and characterized by transmission electron microscopy,infrared spectroscopy,X-ray diffraction,and hysteresis loops.The adsorption and extraction mechanism of this adsorbent on typical pyrethroid pesticides was discussed.The optimal conditions for solid-phase extraction and magnetic separation were discussed.Using HPLC conbined with ultraviolet detection（HPLC-UV）,a rapid,sensitive and reliable method for detecting pyrethroid pesticide residues has been constructed.Under the optimal conditions,four pyrethroids can be determined simultaneously with a detection limit of 2.47-4.87 ng·m L^-1,a relative standard deviation of peak areas between 1.56%-2.00%,and a recovery rate of85.19%-101.12%.Fe₃O₄-NH₂@TpMA magnetic solid-phase extractant was synthesized by a solvothermal method,and its structure was characterized by transmission electron microscopy,infrared spectroscopy,N₂ isotherm adsorption line,hysteresis loop and other means.The mechanism of adsorption and extraction of ester pesticides,along with the optimal conditions for solid-phase extraction and magnetic separation were discussed.Under the optimal conditions,the extraction efficiency of pyrethroids,amide fungicides,and fipronil was discussed.Chromatography-ultraviolet detector has established a simple,sensitive and reliable method for the determination of trace pyrethroids by HPLC-UV.The detection limits of the four pyrethroids ranged from0.67-0.77 ng·mL^-1.The relative standard deviations of the peak areas were between0.21%-0.34%,and the recoveries were between 90.92%-101.77%.Fe₃O₄@mTiO₂@TpBD magnetic composite material was synthesized by a solvothermal method.After a series of characterization,the material was used to extract eight pesticides including pyrethroid,amide fungicides,and fipronil.Combined with HPLC-UV,high sensitivity,simple operation and good repeatability method for the detection of trace pesticide residues in fruits and vegetables has been established.Under the optimal experimental conditions,eight kinds of pesticides can be determined simultaneously with a detection limit of 0.43-2.63 ng·m L^-1,The relative standard deviations of the peak areas were between 0.47%-0.57%,and a recovery rate between 70.88%-103.52%.