Modified Melamine Foam In The Pipette-tip For Solid-phase Extraction Of Organophosphorus Pesticides In Foods

Organophosphorus pesticides（OPPs）,a kind of high-efficiency and broad-spectrum pesticides,are widely used in fruits and vegetables,grains,oil crops,and other fields.Residual OPPs have caused serious pollution to the environment and crops.From farmland to the table,the accumulation of residual OPPs through the food chain may lead to the disturbance of cholinesterase activity in humans,damaging the nervous system or causing serious diseases.Therefore,the rapid analysis method is important to ensure food safety and avoid excessive agricultural residues harming the health of consumers.Due to the complexity of food substrates,the pretreatment of samples before testing is an essential step.Rapid sample pretreatment can effectively improve the analysis efficiency.Pipette-tip solid-phase extraction（PT-SPE）has the advantages of portability,controllability,and easy operation,contributing to achieving rapid extraction of the OPPs.Furthermore,the recoveries of OPPs mainly depend on the selection of adsorbents.Metal-organic frameworks（MOFs）show good adsorption capacity of OPPs due to the large surface area and diverse pore size structure.In this work,the melamine foam（MF）was modified with metal ion and MOFs for PT-SPE.Combined with fluorescence and gas chromatography analysis,rapid extraction of glyphosate in water samples and OPPs in fruit and vegetables was realized,respectively.The main research contents and results are as follows:（1）To achieve rapid extraction of glyphosate in aqueous solution,titanium ion modified MF was prepared.Firstly,polydopamine（PDA）was synthesized by self-polymerization at room temperature on MF substrate,and MF/PDA/Ti⁴⁺was prepared after the titanium ion was immobilized by PDA.MF/PDA/Ti⁴⁺was filled into the pipette-tip,then the PT-SPE method was established to extract glyphosate from aqueous solutions.The morphology,elemental composition and chemical binding state of MF/PDA/Ti⁴⁺were characterized,which confirmed the porous structure of MF and the successful modification of PDA and Ti⁴⁺.The adsorption experiments showed that MF/PDA/Ti⁴⁺had good adsorption ability for glyphosate through electrostatic interaction and there were multiple adsorption active centers on the MF/PDA/Ti⁴⁺.Secondly,the extraction and elution cycles were optimized by filling MF/PDA/Ti⁴⁺into the pipette-tip,and the extraction process could be completed within 2 min.Combined with fluorescence analysis,the limits of detection（LOD）of this method was 4.9μg/L,and this method can be applied in rapid extraction of tap water,lake water,tea drink,and orange juice.In addition,MF/PDA/Ti⁴⁺showed good selectivity for glyphosate while the recoveries for other OPPs were less than 5%.（2）The MF was modified with MOFs to extract multiple OPPs simultaneously.First of all,Ti-MIL-125 and Fe-MIL-101 were presynthesized,which were fixed on MF by polyvinylidene fluoride（PVDF）as the crosslinking agent to prepare MF/PVDF/MOFs.The morphology,crystal structure and functional groups of MF/PVDF/MOFs were characterized,indicating that Ti-MIL-125 and Fe-MIL-101 were successfully synthesized and distributed on MF.The Fe-MIL-101 and Ti-MIL-125 showed good adsorption ability for OPPs,which was mainly due to the hydrogen interaction,π-πinteraction,and the multiple porous structures.Secondly,the extraction conditions were optimized after MF/PVDF/MOFs were filled into the pipette-tip.Combined with gas chromatogram-flame thermionic detector analysis,the LODs of this method were 0.03～0.14μg/L.The PT-SPE method based on MF/PVDF/MOFs was used for rapid extraction of OPPs from fruits and vegetables（<3 min）and the recoveries ranged from 75.3% to 118.8%.