Covalent Organic Frameworks Based Solid Phase Extraction-High Perfromance Liquid Chromatography For The Analysis Of Antibiotic Residues

Antibiotics have been widely used to treat bacterial infections as broad-spectrum antibacterial drugs since its discovery.In recent years,antibiotics residues in the environment and food samples has received extensive attention due to the increasing use of antibiotics.Antibiotic residues will enter the human body through the food chain,causing pathogenic injuries and making people resistant to drugs,posing a serious threat to human health.The quantitative analysis of antibiotic residues still face huge challenges due to low level of residues and complexity of the sample matrix.Solid phase extraction is one of the important techniques for the pretreatment of complex matrix samples due to its advantages of high efficiency,time saving,less consumption of organic solvents,simple operation and easy automation.The key factor to determine the efficiency of solid phase extraction is the performance of the adsorbent material.Covalent organic frameworks are a new generation of porous materials that are constructed from light elements and linked by covalent bonds.They possess many useful properties,such as high surface area,high thermal stability and controllable pore size,which endow them great potential in the analysis of antibiotic residues in food and environmental water samples.Based on the previous report,three covalent organic framework composite materials with high adsorption properties were synthesized and used in solid-phase extraction of antibiotics from animal-derived food and environmental water samples.The main contents are as follows:(1)The covalent organic framework Schiff base network-1(SNW-1)was synthesized based on the Schiff base reaction between terephthalaldehyde and melamine and characterized by scanning electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction and nitrogen adsorption-desorption isotherm analyses.The prepared SNW-1 was employed as pipette tip solid phase extraction adsorbent for the extraction of sulfonamides(SAs)prior to high performance liquid chromatography analysis.The parameters affecting the extraction efficiency,including the salt concentration,sample p H,amount of adsorbent,and eluent type s and volume were investigated in detail.Good linearities were obtained between the peak area and SAs concentration ranging from 5 to 500 ng m L^-1 with correlation coefficients(R²)higher than 0.9998.The limits of detection and RSDs were lower than 0.25 ng m L^-1 and 1.9%,respectively.The de veloped method was further applied for the determination of SAs in milk and honey samples with recoveries in the range of 85.8%-118.0%and RSDs less than 9.5%.The results demonstrate that the SNW-1 shows great potential for the enrichment of trace SAs in complex matrices.(2)A no vel material of COF-LZU1@PEI@Fe₃O₄ was synthesized by immobilization of COF-LZU1 onto the surface of polyethyleneimine-functionalized Fe₃O₄ nanoparticles(PEI@Fe₃O₄)and employed as adsorbent for magnetic solid phase extraction of tetracyclines(TCs).The COF-LZU1@PEI@Fe₃O₄ were characterized by SEM,Fourier transform infrared spectroscopy,X-ray diffraction and nitrogen adsorption-desorption isotherms analysis.COF-LZU1@PEI@Fe₃O₄ were cubic in shape with an average diameter of about 40 nm.The specific saturation magnetization was 64.22 emu g^-1.The BET surface area was about 37.44 m² g^-1 and the average pore diameter was about 30.38 nm.The parameters affecting the extraction efficiency,including the amount of adsorbent,sample p H and volume,extraction temperature and time,type and amount of eluent were investigated in detail.Good linearities were obtained between the peak area and tetracyclines concentration ranging from 5-500 ng m L^-1 with correlation coefficients(R²)higher than 0.9992and limits of detection lower than 0.51 ng m L^-1.The relative standard deviations(RSDs)of intra-day and inter-day were less than 5.7%and 7.4%,respectively.The developed method was successfully applied to the determination of tetracyclines in different environmental water samples with recoveries in the range of 87.0%-113.8%.(3)The core-shell structured magnetic covalent organic framework(Fe₃O₄@Tb Bd)adsorbent was de veloped for magnetic solid phase extraction(MSPE)of fluoroquinolones(FQs).The Fe₃O₄@Tb Bd were characterized by SEM,Fourier transform infrared spectroscopy,X-ray diffraction and the nitrogen adsorption-desorption isotherms analysis.Fe₃O₄@Tb Bd were spherical in shape with an average diameter of about 200 nm.The BET surface area was about 33.48 m² g^-1and the average pore diameter was about 19.45 nm.The specific saturation magnetization was 35.16 emu g^-1.The extraction conditions of three FQs were systematically optimized.The effects of the amount of adsorbe nt,sample volume,extraction time and temperature,sample p H,type and volume of eluent of three FQs were investigated.Good linearities were obtained between the peak area and FQs concentration ranging from 1-500 ng m L^-1 with correlation coefficients(R²)higher than 0.9991,limits of detection lower than 0.13 ng m L^-1.The relative standard deviations(RSDs)of intra-day and inter-day were less than 3.9%and 5.8%,respectively.The accuracy of the developed method was e valuated by measuring the extraction recovery of different river water samples,with recoveries in the range of83.7%-108.5%.