Solid-phase Microextraction Based On Carbon Fiber Brush And Its Application In Environmental Analysis

As an excellent sample pretreatment technique,solid-phase microextraction（SPME）has attracted more and more attention.In order to extract various analytes in different samples,SPME has been developed into a variety of forms.Fiber SPME is the earliest form,which integrates sampling,extraction,concentration,purification,and sampling injection into one single step.It is a green sample preparation method with no or only less organic solvent.Although it stands out in the field of sample pretreatment,it still has some shortcomings.Only one fiber for extraction greatly limits the amount of extraction coating and the number of adsorption sites,resulting in low extraction capacity and low extraction efficiency.As one of the four functional fibers in China,carbon fibers have the characteristics of micron diameter,excellent mechanical property,and graphitization structure on the surface.They also have good adsorption performance for hydrophobic organic compounds,and have a wide application prospect in aerospace,water pollution treatment,and other fields.The brush of carbon fibers consists of a large number of carbon fibers with micron diameter,making it has high adsorption surface area.The brush can not only be directly applied as a SPME material,but also be used as a support,which can be modified with the extraction coating,effectively increasing the adsorption sites and further improving the extraction efficiency.Based on these consideration,the research ideas are as follows:firstly,a brush of carbon fibers is prepared from a commercial bar of carbon fibers,and introduced into SPME field to develop“brush solid-phase microextraction”.Combined with gas chromatography,a method was established for the analysis of trace polycyclic aromatic hydrocarbons（PAHs）in environmental water samples.Furthermore,covalent organic frameworks（COFs）with high surface area and excellent pore structure were used to functionalize the brush of carbon fibers.Nano-COFs coating was in-situ grown onto the surface of carbon fibers,and a high-performance"brush solid-phase microextraction"material was developed for the highly sensitive detection of PAHs in real water samples.（1）Research and application of the brush of carbon fibers for solid-phase microextractionThe commercial carbon fiber bar was burned to prepare the brush of carbon fibers,which was introduced into SPME field as a new extraction material.The SPME material possesses a large number of carbon fibers,which overcomes the problem about only a single extraction fiber in the traditional SPME.Scanning electron microscopy,Raman spectroscopy,and X-ray photoelectron spectroscopy were used to characterize the surface morphology and chemical composition of the fibers in the brush,and the excellent physical and chemical properties were confirmed.Combining carbon fiber brush-based SPME with gas chromatography,the extraction conditions（extraction time,extraction temperature,stirring rate,and ionic strength）and desorption time were optimized.The optimal extraction conditions were determined as 30^oC of extraction temperature,30 min of extraction time,1600 rpm of stirring rate,20%（w/v）of KCl in the sample,and 3.0 min of desorption time at 300 ^oC.The method was established under the optimal conditions with high sensitivity(limits of detection,0.01-0.20μg L^-1)and wide linear concentration range(0.60-100μg L^-1).Finally,the analytical method based on carbon fiber brush was evaluated by detecting trace PAHs in environmental water samples,and the relative recoveries were 86.1%-116%.（2）Research and application of covalent organic frameworks functionalized carbon fiber brush for solid-phase microextractionUsing a carbon fiber brush as a support,1,3,5-tris（4-aminophenyl）benzene and1,4-divinyl-2,5-diuronic benzene as the monomers,a coating of nano-COFs particles was in-situ grown on the surface of carbon fibers by Schiff base reaction at room temperature.The preparation of COFs coating was optimized by controlling the concentration of monomers.The COFs coating was characterized by scanning electron microscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The COFs coating not only increased the surface area of fiber brush for extraction,but also provided strongπ-πstacking and hydrophobic interactions towards PAH analytes,which can effectively improve the extraction efficiency.Therefore,a novel high-performance brush-based SPME material was developed.The extraction and desorption conditions were optimized by selecting the COFs-functionalized carbon fiber brush with the best extraction efficiency.An efficient（extraction time,40 min）and sensitive(limits of detection,0.005-0.05μg L^-1)method was established for the determination of PAHs.The method was successfully applied for the analysis of actual samples and satisfactory results were obtained.The extraction performance of carbon fiber brush before and after the functionalization of COFs was compared.The results showed that the extraction capacity of COFs coating was 5.8-14 times of that from bare carbon fiber brush.Compared with several common commercial SPME fibers（75μm PA,100μm PDMS,and 50/30μm DVB/CAR/PDMS）,the COFs-coated carbon fiber brush showed better extraction performance for the highly hydrophobic analytes.Its extraction capacity was 2.1 to 8.8 times that of commercial SPME fibers.