| Solid-phase microextraction(SPME),based on the distribution equilibrium between sample and extraction coating,is a simple,convenient,efficient,solvent-free and environment-friendly sample pretreatment technique.SPME integrates sampling,extraction,concentration and injection into one step,and has been widely used in environmental monitoring,drug analysis and food safety and medical research.In-tube solid-phase microextraction(IT-SPME)performed extraction by an extraction tube,can be easily combined with high performance liquid chromatography(HPLC)for on-line detection of various targets.The extraction coating plays a critical role in sensitivity,capability and repeatability.Organic aerogels are potential extraction materials for IT-SPME because of their unique three-dimensional network structure,high nano porosity,low density,huge surface area and good mechanical strength.Melamine-formaldehyde(MF)aerogel,as a typical organic aerogel,has displayed excellent extraction performance in sample preparation.However,there are some weaknesses such as poor extraction selectivity and efficiency,long gel reaction time,which limit its further development and application.Previous studies have shown that nanomaterials can overcome the defects of MF aerogel.In this paper,boron nitride nanosheets(BNNs),graphene oxide(GO)and silver nanoparticles(Ag NPs)were chosen to functionalize MF aerogel to obtain new extraction materials,which were introduced into IT-SPME as extraction coatings.And then several new extraction tubes were developed and evaluated by coupling with HPLC.Some analytical methods were established and applied to the detection of trace polycyclic aromatic hydrocarbons(PAHs)in drinking water,environmental water and soil.The main contents and results are as follows:1.Basalt fibers,as one of the four high-performance fibers developed in China,were selected as the substrate on which BNNs functionalized MF aerogel coating were in-situ prepared for IT-SPME.The coating was characterized by scanning electron microscopy(SEM)and dispersive X-ray spectroscopy(EDS).A bundle of basalt fibers coated with aerogel was placed into polyetheretherketone(PEEK)tube to obtain fibers-filled SPME tube.Combining the tube with HPLC-DAD,the extraction selectivity was investigated using several types of organic compounds(plasticizer,estrogen and PAHs),PAHs were chosen as the model analytes for further testing.The introduction of BNNs increased the enrichment capacity of MF aerogel to 1.1-5.7 times.The main factors of the extraction efficiency,such as sampling volume,sampling rate,methanol content and desorption time,were investigated and optimized.Under the optimum conditions(extraction volume of 70 m L,sampling rate of 2.00 m L min-1,methanol content of 1.0%(v/v),desorption time of 2.0 min),the online IT-SPME-HPLC-DAD method was established with good linearity in the range of 0.030-20?g L-1(r?0.9990),and limits of detection(LODs)were in the range of 0.005-0.010?g L-1.Compared with other analytical methods,the method has better sensitivity as well as shorter extraction time.The method was finally successfully used to the determination of trace PAHs in rainwater and soil samples and the spiked recoveries ranged from 81.3%to 120.0%.2.GO was used to modify MF aerogel for getting GO/MF aerogel composite,which was coated onto the surface of stainless steel wire as a extraction coating.The GO/MF aerogel coating was characterized by SEM and X-ray photoelectric spectroscopy(XPS),indicating that GO was successfully introduced into MF aerogel and the porosity of MF aerogel was improved.Four modified wires were placed into a PEEK tube(0.75 mm i.d.,30 cm)to develop a new extraction tube.Coupling with HPLC,the tube demonstrated excellent extraction capacity for PAHs,and GO increased the capacity of MF aerogel to 2.5 times.The main extraction and desorption conditions were optimized,and then the online IT-SPME-HPLC-DAD analytical method was established.The LODs of eight PAHs were0.001-0.005·?g L-1,the quantitative detection range of the analytes was 0.003-20·?g L-1,and the analytical precision was good(intra-day RSD%?4.8%,inter-day RSD%?8.6%).Higher sensitivity,wider linear range,and shorter extraction time than that from some reported methods.It proved that the method is suitable for highly selective and sensitive detection of PAHs from real sample.In addition,the tube has good stability and can be applied to weakly acidic or alkaline samples.3.Based on the coordination effect of Ag NPs and aromatic compounds,Ag NPs were used to functionalize MF aerogel for improving the extraction ability for PAHs.Ag NPs were grown onto the surface of MF aerogel by in-situ reduction reaction,and the prepared Ag NPs/MF aerogel was coated onto the surface of stainless steel wire as a new extraction material.Then the wires were packed into PEEK tube.By means of SEM,XPS and X-ray powder diffraction,the concentration of silver nitrate in reduction reaction was optimized,and Ag NPs/MF aerogel with optimal extraction efficiency was obtained.The LOD was as low as0.003·?g L-1,and the enrichment effect was as high as 1998-3237.The sensitivity of HPLC-DAD was improved by three orders of magnitude,and the highly sensitive analysis and detection of trace PAHs in drinking water and environmental water samples were realized.The extraction capacity of MF aerogel for PAHs was improved by 166.4%due to Ag NPs.The method in this study shows stable extraction performance and satisfactory recovery,so the Ag NPs/MF aerogel has a good application prospect in IT-SPME.Compared with other methods for detection of PAHs,the LODs and linear range of the method are close to or better than others,but the sensitivity needs to be further improved.MF aerogel was functionalized with BNNs and modified on the surface of basalt fibers.It can not only support the aerogel skeleton structure,but also enhance the interaction between the extraction coating and PAHs.The introduction of GO increases the porosity of MF aerogels and improves the mass transfer efficiency in the extraction process.Meanwhile,GO and PAHs can produce?-?interaction,which enhances the extraction efficiency of functionalized aerogels for PAHs.Ag NPs were modified onto the surface of MF aerogel,which increased the adsorption site for the analyte and significantly improved the extraction efficiency of aerogel.The introduction of three nanomaterials has significantly improved the mechanical strength and adsorption properties of MF aerogels,which can expanded the types and application prospects of aerogels.The method of in-situ growth of aerogel coating on the surface of basalt fibers with micron diameter can load more aerogel material than those aerogel coatings on the surface of stainless steel wire,which is more conducive to obtain high enrichment capacity.The combination between IT-SPME and HPLC for online test,not only save time but also improve the accuracy of analysis and detection. |
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