Preparation Of Novel Porous Materials-based Solid Phase Microextraction Fibers For The Determination Of Some Environmental Pollutants

The residues of organic compounds in environmental samples are directly related to human health and life safety,and they have become a focus of public concerns.Strengthening the detection of organic pollutants in the environment is of great significance for ensuring people’s health.However,a wide range of environmental pollutants,matrix complexity,the target analytes is low,which greatly increased the difficulty of the analysis.Sample preparation can reduce or eliminate matrix interferences and can concentrate analytes for trace analysis purposes.As a simple and efficient sample preparation technique,solid-phase microextraction（SPME）can integrate sampling,extraction,concentration and sample introduction into a single step.SPME has been widely applied in food,environmental and biological analysis due to its advantages such as simplicity,efficiency,ease of operation,and lack of solvent consumption.In this thesis,several analytical methods were developed for the sensitive determination of some pesticide residues or organic pollutants in fruit,vegetable or environmental samples by SPME technique coupled with gas chromatography-micro-electron capture（GC-μECD）,or gas chromatography-mass spectrometry（GC-MS）detection.The thesis is mainly concerned with the following aspects:（1）A novel covalent organic framework,Schiff base network-1（SNW-1）,was synthesized and used as a solid-phase microextraction（SPME）fiber coating material.The SNW-1 coated SPME fiber was fabricated by a covalent chemical cross-linking between the SNW-1 nanocomposite and a silanol-functionalized stainless steel wire substrate.Scanning electron microscopy and nitrogen isothermal adsorption results indicate that the new fiber coating exhibited a porous,homogenous surface with the Brunauer-Emmett-Teller surface of 668 m^2/g.The prepared fiber was explored for the SPME of phenols from honey samples prior to their determination by gas chromatography-mass spectrometry.The developed method had large enrichment factors（136⁸16）,low limits of detection（0.06⁰.2 ng/g）,good linearity(0.1¹00.0 ng/g and repeatability（<9.7%）for phenols.The recoveries for spiked phenols（1.0 ng/g and 10.0 ng/g）in wolfberry,robinia and codonopsis honey samples were in the range of 84.2%¹07.2%with the relative standard deviations ranging from 3.8%to 12.7%.The developed method was suitable for the determination of phenols from honey samples.（2）A porous aromatic framework of type PAF-6 was synthesized and explored as a coating onto a steel wire for use in solid-phase microextraction of polycyclic aromatic hydrocarbons（PAHs）,phthalate plasticizers,and n-alkanes.The extraction temperature,extraction time,salt concentration,agitation speed,desorption temperature,and desorption time were optimized.This method for SPME resulted in the enrichment factors ranging from122 to 1090 for PAHs（naphthalene,acenaphthene,fluorene,phenanthrene,anthracene,fluoranthene,pyrene）,from 122 to 271 for plasticizers（diisobutyl phthalate,dibutyl phthalate,benzyl butyl phthalate,dicyclohexyl phthalate）,and from 9 to 113 for n-alkanes（n-undecane,n-dodecane,n-tridecane,n-tetradecane,n-pentadecane,n-hexadecane,n-octadecane and n-eicosane）.The good extraction of the PAHs is assumed to be due to theirπ-stacking interaction and hydrophobic effect.The PAF-6 coated fibers are durable and can be reused more than 100 times without significant loss of extraction performance.In combination with GC-MS detection,the method has limits of detection in the range from 0.8to 4.2 ng/L in case of PAHs.The relative standard deviations for five replicate determinations of the PAHs by using one fiber are in the range from 5.2%to 8.5%.When using different fibers,they range from 7.1%to 9.6%.The recoveries of PAHs from water samples at a spiking level of 20 ng/L are in the range from 89.5%to 103.1%,with relative standard deviations ranging from 4.0%to 9.3%.（3）A hyper-crosslinked polymer benzenedimethanol,HCP-BDM,was synthesized and explored as a solid-phase microextraction（SPME）fiber coating material.To prepare the HCP-BDM,1,4-benzenedimethanol monomer was self-condensed via a simple Friedel-Crafts alkylation reaction.The physical-chemical properties of the HCP-BDM material were studied with scanning electron microscopy,nitrogen adsorption-desorption isotherms,thermogravimetric analysis and infrared spectroscopy.The HCP-BDM coated fiber demonstrated excellent adsorption performance for some organochlorine pesticides（OCPs）.A facile and effective HCP-BDM-assisted SPME method combined with gas chromatography-micro electron capture detection was developed for the determination of the OCPs from various vegetable samples.The linear ranges were observed from their corresponding limits of quantification（LOQs）to 50 ng/g for the OCPs,with the correlation coefficients of 0.9952⁰.9992.Their limits of detection for the OCPs at S/N=3 were in the range of 0.058 ng/g⁰.14 ng/g.The relative standard deviations（RSDs）for the fiber repeatability and fiber-to-fiber reproducibility were from 3.4%to 8.8%and from 6.7%to9.6%,respectively.The established method was finally applied to the determination of the OCPs from cucumber,Chinese cabbage and tomato samples with satisfactory recoveries and repeatability.（4）In this work,we present a facile and economical approach to synthesize a nanoporous carbon via a KOH chemical activation process using waste pomelo peels as the biomass precursor.The nanoporous carbon derived from pomelo peels exhibits a nanoporous structure（pore size,0.69 nm）and high surface area（1770 m²/g）.To evaluate the extraction performance of the nanoporous carbon,it was applied as a solid-phase microextraction coating for the enrichment of benzene homologues from water and soil samples prior to their determination by gas chromatography-mass spectrometry.The main influencing experimental parameters for the extraction were investigated and optimized.Under the optimum conditions,a good linearity for the signal response was achieved in the concentration range of 0.4 ng/L¹00.0 ng/L for water samples and 5.0 ng/kg¹000.0 ng/kg for soil samples with the determination coefficients（r）larger than 0.9989.The limits of detection（S/N=3）of the method ranged from 0.05 to 0.18 ng/L for water samples and from0.11 to 0.18 ng/kg for soil samples,respectively.The recoveries of the analytes were in the range of 81.3%¹12.0%with the relative standard deviations（RSDs）ranging from 1.5%to11.4%（n=5）.The single fiber repeatability and fiber-to-fiber reproducibility values expressed as RSDs were in the range of 2.4%⁸.1%and 5.9%⁹.9%,respectively.The method was simple,convenient and feasible for the determination of benzene homologues in real samples.