Research Of Solid Phase Micro-extraction Method And Pretreatment Coupled With GC-MS For Determination Of Persistent Organic Pollutants In Environment And Food

Polychlorinated biphenyls?PCBs?,a type of persistent organic pollutants,possess highly toxicity and carcinogenic.PCBs are easily deposited in the soil and can be enriched in the body through the food chain,which will harm the health of the public.So,it has become more important to detect PCBs in environment and foods.However,the content of PCBs in the environment and food is extremely low,and the sample matrix is more complicated,which brings great difficulties to the detection.Therefore,pre-processing is one of the key factors to detect PCBs.The traditional pretreatment methods,such as liquid-liquid extraction and solid-phase extraction,are often cumbersome and require a large amount of organic solvents,which will harm the environment and operators.Therefore,there is an urgent need to develop high-efficiency,green pretreatment methods for the determination of PCBs.In recent years,solid-phase microextraction?SPME?technology has been widely used in the detection of PCBs in the environment and food.The reason was due to that SPME is a simple,fast and environmentally friendly pre-processing method.As we all know,the key of solid-phase microextraction technology is to make coatings with high-adsorption amount and-selectivity.However,commercialized coatings are fragile and have some drawbacks in terms of selectivity and extraction efficiency.In this thesis,metal organic frameworks,covalent organic framework materials,MoS₂,TiO₂ have been introduced to improve the selectivity and sensitivity of coatings.Water was used as the extraction solvent in this study.With the aid of external forces?such as ultrasound-assisted,saponification,sealed heating?,the extraction efficiency is further increased.SPME with GC-MS method enables highly sensitive and high-throughput rapid detection of PCBs in environmental and food.This article is mainly divided into the following three aspects:1.Herein,an ultrasonic-assisted headspace solid phase micro-extraction?UA-HS-SPME?method was studied for extraction of 7 indicator PCBs:PCB28,PCB52,PCB101,PCB118,PCB138,PCB153,PCB180 from soil samples based on a novel poly-dopamine-metal-organic frameworks coated fiber?PDA-MIL-53?Fe??.The coating can be easily prepared and evenly covered on a stainless fiber by dipping the PDA fiber into the MIL-53?Fe?solution repeatedly for five times.The UA-HS-SPME assay is also environmentally friendly just by using water as solvent while not organic reagents then employing ultrasonic to assist the extraction.In order to obtain the best extraction efficiency,different experimental conditions were investigated,such as extraction time,addition of salts,pH and power of ultrasonic power.The optimum conditions are as following:10 g soil samples were blended with equal amount of water and loaded in 40 mL sealed headspace vial.Then the PDA-MIL-53?Fe?coated fiber was inserted in headspace of vial to extract PCBs for 60 min with the aid of 90W ultrasonic power at ambient temperature.The MIL-53?Fe?coating has higher selectivity and adsorption capacity to PCBs than the commercial SPME fibers such as Divinylbenzene/Carboxen/Polydimethylsiloxane.With the aid of ultrasonic wave,the developed UA-HS-SPME method only needs water as solvent and the extraction effectiveness can be further improved.The extracted PCBs presented favorable linearity with correlation coefficients of more than 0.992.The low detection limits for the seven PCBs can reach to between 0.05 and0.09 ng g^-1 using gas chromatography-mass spectrometry?GC-MS?for measurement.The novel fibers can be easily prepared and the batch-to-batch reproducibility was good with RDS<10%after being assessed on six independently synthesized preparations.And the developed SPME assay proved to be costless,reusable and easy for manipulation which enables it as a good candidate screening method for investigations of PCBs in environmental samples.2.Molybdenum disulfide/reduced graphene oxide?MoS2/RGO?composite material was synthesized as coating of fiber to extract seven indicator PCBs with codes of PCB28,PCB52,PCB101,PCB118,PCB138,PCB153,and PCB180 in food via a saponification-headspace solid-phase microextraction assay?saponification-HS-SPME?.The MoS₂/RGO coating was prepared and deposited on the stainless fiber with the help of silicone sealant as a probe.Alkali solution was used to dissolve fat and help releasing the PCBs to headspace for extraction under 100?.Following desorption in inlet,the targets were quantified by GC-MS.The effects of sorbent dosage,extraction time,added salts and stirring rate on extraction efficiency were investigated.The new coating is found to possess a higher adsorption amount for analytes which is about 1.1-2.9 folds comparing to the commercial SPME fiber which showed the highest adsorption of PCBs?divinylbenzene/carboxen/polydimethylsiloxane?and 1.5-2.7 folds to prepared RGO modified fiber.MoS₂ which was grown on the layers of RGO and formed pores,maybe play a key role in the enhanced adsorption capacity of graphene.Moreover,MoS2 also have strong affinity towards PCBs like graphene.The method is simple and environmentally friendly without any organic solution,and has good sensitivity,with detection limits less than 0.1 ng/mL,linearity?0.25-100ng/mL?and reproducibility?RSD?below 10%?for n=3?.The novel SPME fibers are inexpensive,reusable and can be easily prepared and manipulated.Moreover,the saponification-HS-SPME assay is enviromenatlly friendly for screening persistent organic polluants in dairy products.3.Herein,a kind of magnetic titanium dioxide@covalent organic frameworks?Fe3O4@TiO2@COFs?composite was synthesized as coating on Nd–Fe–B magnets for stir bar sorptive extraction?SBSE?of seven indicator polychlorinated biphenyls in vegetables.The Fe3O4@TiO2@COFs was prepared through assembly strategy using hydrothermal method.Then the stir bar was used to extract PCBs in vegetable samples.After being desorbed in n-hexane under strring,the analytes were measured by gas chromatography-mass spectrometry?GC-MS?.The advantages of assay are as following:The newly developed coating has three advantages.First,COFs possesses uniform structured cavities with pore size of 3.5 nm;thus PCBs whose size was less than 2 nm can freely pass through it,while the larger macromolecular impurities,e.g.protein and cellulose in complex vegetable matrices was excluded.Second,the inner flower-like mesoporous TiO₂ coating has good affinity towards some chlorine-containing organic compounds,which further enhances the selectivity of the coating to PCBs.Third,both TiO₂ and COFs have large specific surface area,the composite coating exhibit should high adsorption capacity towards PCBs because of the synergistic effects.Under the optimal conditions,the limits of detection?S/N=3?was measured(less than 0.1 ng g^–1),which exhibited good extraction capacity and selectivity.Moreover,it also showed good satisfactory linear ranging from 0.01 to 100 ng g^–1.Furthermore,the fabricated stir bar can be reused at least for 80 times with the recovery above 80%.Therefore,this method can be applied to the determination of PCBs residues in vegetables.