Determination Of Some Pollutants In Food And Environmental Samples By Solid Phase Microextraction With New Fibers Combined With Gas Chromatography

The residues of toxic compounds in food and environmental samples directly harm human health and life safety.Therefore,it is necessary to establish a sensitive and accurate measurement method to detect the residual amount of harmful substances in food and environmental samples.Due to the complex matrix of food and environmental samples,and the low content of target analytes,sample pretreatment is often necessary.To isolate the target analytes from samples,reduce or eliminate matrix interference,and to concentrate the target analytes for trace analysis purpose.Solid phase microextraction?SPME?is a green,solvent-free new sample pretreatment and it has received much attention due to its high extraction efficiency and ease of integration with other analytical instruments.Fiber coating is the core of the SPME technology.Although there are some commercial fiber coatings available today,the variety of them is still limited.Therefore,research on the development of novel fiber coatings is still a hot topic.In this thesis work,three different adsorbent materials were prepared and used to fabricate three different SPME fibers by applying sol-gel technique and physical coating method to coat them onto treated stainless steel wires.Then,the SPME methods with those fibers couped with gas chromatography or gas chromatography mass spectrometric detection were eatabolished for the determination of different types of organic pollutants?pesticides,polycyclic aromatic hydrocarbons,phthalate esters?in food and environmental samples.The thesis mainly involves the following research works:1.A covalent organic framework designated as TpPaNO₂ was synthesized by mechanochemical grinding method and then coated on stainless steel wire by sol-gel technique to prepare SPME fiber.The TpPaNO₂ fiber based SPME coupled with gas chromatography-electron capture detection was applied to determine the residues of eleven pesticides?trlfuralln,dicofol,?-endosulfan,p,p'-DDE,nitrofen,?-endosulfan,p,p'-DDD,p,p'-DDT,bifenthrin,permethrin and fenvalerate?in vegetable and fruit samples.The effects of extraction time,extraction temperature,sample pH,stirring rate and desorption temperature on the extraction efficiency were investigated.Under the optimized conditions,a good linearity for the signal response was achieved in the concentration range of 0.5-225?g kg^-1 for vegetable and fruit samples,and the limits of detection for the eleven pesticides were in the range of 0.04-0.25?g kg^-1.The recoveries of the eleven pesticides in the vegetable and fruit samples were 81.5%-111%with the relative standard deviations less than 11.2%.2.Stober method was used to synthesize carbon nanospheres with a uniformly distributed spherical morphology and a specific surface area of 776 m² g^-1.SPME fibers were prepared by using the carbon nanospheres as the coating materials.The fibers used to the SPME eight polycyclic aromatic hydrocarbons?Naphthalene,Biphenyl,Acenaphthene,Fluorine,Phenanthene,Anthracene,Fluoranthene and Pyrene?from water and soil samples.The experimental parameters which affect the extraction efficiency?extraction temperature,extraction time,stirring rate,headspace volume,salt content,desorption temperature?were studied.Under the optimized conditions,good linearity was obtained in the concentration range of 0.5-300?g L^-1 for water samples,and in concentration range of 6.0-2700?g kg^-1for soil samples,the detection limits for water samples were in the range of 0.12-0.45?g L^-1,and the detection limit for soil samples were in the range of 1.53-2.70?g kg^-1.The recoveries for water samples spiked with the eight polycyclic aromatic hydrocarbons were80.10%-120.1%with relative standard deviations less than 13.9%.The recoveries for soil samples were 80.40%-119.6%with relative standard deviations less than 14.4%.The method was simple,and suitable for determining the residues of polycyclic aromatic hydrocarbons in water and soil samples.3.Porous boron nitride with large surface area was synthesized by high temperature carbonization using melamine,urea and boric acid as precursors.The prepared porous BN was then coated onto a stainless steel wire by physical coating method for the preparation of SPME fibers.The prepared fibers were used for the SPME of seven phthalate esters?Diethyl phthalate?DEP?,Diallyl phthalate?DAP?,Diisobutyl phthalate?DIBP?,Dibutyl phthalate?DBP?,Butylbenzyl phthalate?BBP?,Dicyclohexyl phthalate?DCHP?,Di-2-ethylhexyl phthalate?DEHP??prior to their gas chromatography-mass spectrometric?GD-MS?detection.The experiments were conducted to optimize the experimental parameters for both the extraction and desorption steps,respectively.The single factor method for the paeameter of desorption temperature and the response surface method of central composite design?CCD?for the paeameter of the extraction time,extraction temperature,salt concentration and stirring rate were performed.Under the optimized experimental conditions,the linear range of the analytes for beverage samples with this method was between 0.03 and 30?g L^-1,the detection limits for bottled beverage samples were 0.01-0.04?g L^-1.The recoveries for spiked phthalate esters in bottled beverage samples were 82.95%-109.0%with relative standard deviations less than 11.9%.