Stir Bar Sorptive Extraction Based On Imine-linked Covalent Organic Frameworks For The Determination Of Trace Organic Pollutants Followed By High Performance Liquid Chromatography

Stir bar sorptive extraction(SBSE)is a kind of novel sample pretreatment technique with the advantages of simple operation,low consumption of chemical reagents and good reproducibility.In addition,SBSE also possesses the merit of high recoveries because the volume of extraction phase is larger than that of solid phase microextraction.As an environmentally friendly sample pretreatment technique,SBSE has been successfully applied in the separation and enrichment of organic pollutants.Up to now,several commercial coatings for SBSE have arisen for applications in the daily production and life.However,the varieties of these commercial coatings are limited,restricting wide applications of SBSE,and they also suffer from low extraction efficiency and slow extraction kinetics,which cannot satisfy the growing demands for analysis.Therefore,exploring new coatings with excellent performance and selectivity is beneficial to the development of SBSE.In recent years,covalent organic framework materials(COFs),a new type of porous polymers with large conjugated systems and rich pore structures,have become a kind of ideal adsorbent with great application potential.Moreover,COFs can be easily functionalized by selecting suitable monomers or post-synthesis modification to significantly improve its adsorption selectivity.Nowadays,COFs has been used as adsorbent in a variety of sample pretreatment techniques for the extraction of organic pollutants,but it is still in its infancy.Meanwhile,COFs with excellent performance are yet to be developed,and its application in SBSE needs to be further expanded.The purpose of this thesis is to prepare functionalized COFs by one-step synthesis method as SBSE coating materials,fabricate functionalized COFs coated stir bars via simple physical adhesive method,and ultimately establish new methods of SBSE coupled with high performance liquid chromatography(HPLC)-ultraviolet detector(UV)to analyze trace organic pollutants in different samples.The research contents are as follows:(1)An imine-linked COF named TAPB-DMTP-COF was synthesized from 2,5-dimethoxybenzene-1,4-dialdehyde(DMTP)and 1,3,5-tris(4-aminophenyl)benzene(TAPB)by simple room temperature synthesis method.The prepared COF showed a large specific surface area(2459 m~2/g),hydrophobic skeleton and abundant methoxyl group.Subsequently,it was coated on a bare glass stir bar by physical adhesion method to obtain TAPB-DMTP-COF coated stir bar for the extraction of non-steroidal anti-inflammatory drugs(NSAIDs).The self-made stir bars exhibited higher extraction efficiency(74-85%)and faster dynamics(50 min)towards NSAIDs over commercial ethylene glycol-Silicone(EG-Silicone)and polydimethylsiloxane(PDMS)coated stir bars(3-68%,180 min),and could be reused for 60 times with good mechanical properties.Based on it,a method of SBSE-HPLC-UV was constructed for the determination of four NSAIDs in environmental water samples.Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),zeta potential and water contact angle were used to study the adsorption mechanism between the coating and target analytes.It was preliminarily proved that the hydrogen bond formed between methoxyl group on TAPB-DMTP-COF and carboxyl on NSAIDs promoted the extraction.Additionally,π-πinteraction and hydrophobic interaction also contributed to the extraction.Under the optimized conditions,the linear range of the established method for interest NSAIDs was 0.2/1-500μg/L with limits of detection(LODs)varied from 0.039 to 0.312μg/L.The proposed method was applied for trace analysis of NSAIDs in Yangtze River water,East Lake water and Spring water samples,the recoveries in corresponding spiked samples were 84.7-104%,81.2-101%and 82.6-97.6%,respectively.(2)A fluorinated COF(COF-F-2,with fluoride content of 15.69%)was successfully fabricated from 2,3,5,6-tetrafluoro-1,4-benzenedimethanol and 1,3,5-tri(4-aminophenyl)benzene.Because of the fluorine-fluorine interaction,COF-F-2 may be an ideal extraction coating material for benzoylurea insecticides(BUs)composed of fluorine atoms,benzene rings and urea bridges.Based on it,COF-F-2 coated stir bars were prepared via physical adhesion method,and a new method of COF-F-2-SBSE-HPLC-UV was established for the determination of five BUs(diflubenzuron,hexaflumuron,novaluron,teflubenzuron and fluazuron)in pear juice and pear beverage samples.The extraction performance of home-made coated stir bars for five BUs was better than that of commercial EG-Silicone and PDMS coated stir bars(51-83%vs 4-42%).Meanwhile,COF-F-2 coated stir bars could be reused for 65 times,indicating that the self-made stir bars possessed admirable mechanical property.The adsorption behavior of BUs on COF-F-2 was studied by theoretical calculation and spectral characterization,along with adsorption experiment.The results revealed that interest analytes were adsorbed in the channels of COF-F-2 mainly through the halogen bond(O-F),hydrophobic interaction,electrostatic interaction andπ-stacking interaction.Under the optimal conditions,the linear range of the established method was 1.0/2.0-500μg/L,and the LOD was 0.301-0.672μg/L.The method was applied to the determination of BUs in pear juice and pear beverage,and none of the five target analytes were detected.A recovery experiment was conducted for these two samples,the spiked recoveries were 82.0-113%and 84.0-112%,suggesting that the established method was appropriate for the analysis of BUs in complex samples.