| As an indispensable part of agricultural production,pesticides are used extensively to increase crop yields.As a kind of food additives,preservatives can prolong the storage time of food by inhibiting the growth of microorganisms.However,excessive and unreasonable use of pesticides and preservatives can cause pollution of water bodies,soil,agricultural products and food.Therefore,it is particularly important to develop a fast,efficient,and low-cost sample preparation technology to cope with the trace detection of contaminants in complex matrix samples.In the work of this thesis,we developed five sample pretreatment techniques based on metal organic framework materials to extract triazine herbicide residues and paraben preservatives from food and environmental samples.High performance liquid phase chromatography-tandem mass spectrometry was employed for highly sensitive and selective detection of targets.A metal-organic framework material MIL-101(Cr)was prepared and used as the sorbent for a laboratory-made semi-automated microextraction in packed syringe(MEPS).Six triazine herbicides,including desmetryn,prometon,ametryn,prometryn,atraton,and dipropetryn,that are commonly found in corn samples,were extracted and determined by the MEPS method and high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS).Key parameters affecting the extraction efficiencies,including type of extraction solvent,type and amount of sorbent,time of ultrasonic extraction and adsorption,and type,volume and flow rate of elution solvent,were investigated.The limits of detection(LODs,S/N=3)and quantification(LOQs,S/N=10)for all analytes obtained by the proposed method were in the ranges of 0.014-0.116 ng g-1 and 0.043-0.348 ng g-1,respectively.These findings indicated that the proposed semi-automated MEPS method was easy and efficient for the extraction of triazine herbicides in corn samples.A simple and efficient integrated,laboratory-made,semi-automatic microextraction packed in a syringe(semi-automated MEPS)was first assembled and validated for the extraction of parabens in vegetable oils.Several representative metal-organic frameworks were prepared and used as sorbents for the direct extraction of analytes from diluted vegetable oils in a sealed syringe.The sorbent and adsorbed analytes were collected by an organic filter after syringe injection.After extraction,a simple device was used for the elution of analytes,which could greatly simplify the operation and reduce the total pretreatment time for oil matrix.HPLC-MS/MS was used to separate and quantify parabens.Key factors affecting the extraction efficiency were investigated,such as volume ratio of oil sample to n-hexane,ultrasound extraction time,type and amount of sorbent,as well as the type,volume,and flow rate of elution solution.Under optimal conditions,the proposed method achieved low limits of quantification(1.97-4.57ng mL-1).Relative standard deviations were calculated for all herbicides at two concentrations levels and were below 14.0%.Cellulose paper was coated with the metal-organic framework MIL-101(Cr)in a chitosan matrix and utilized for thin-film microextraction(TFME).The coated paper possesses excellent extraction efficiency for the triazine herbicides atraton,desmetryn,secbumeton,prometon,ametryn,dipropetryn,and dimethametryn.HPLC-MS/MS was applied to quantify target analytes.The effects of mass ratio of MIL-101(Cr)to chitosan,sample p H value,time of adsorption and desorption,and type and volume of desorption solvent on extraction efficiency were optimized.Under the optimal conditions,the method has limits of detection between 1.5 and22 ng L-1.The recoveries of triazines from spiked tap water,drinking water,lake water and river water range from 77.1 to 125.3%.The experimental results show that the use of cellulose acetate paper as the base material can significantly simplify the adsorption and desorption steps in solid phase extraction while saving sample pretreatment time.Several metal-organic framework-modified melamine sponge columns were first developed and used as laboratory-made solid-phase extraction columns.They were then filled in the cavity of medical syringes for the extraction of six triazine herbicides in vegetable oils.HPLC-MS/MS was used to characterize and quantify the target triazine herbicides.The metal-organic framework-sponge columns were prepared using a simple approach by embedding the solid particles in melamine sponge using polyvinylidene difluoride physical encapsulation.The method was applicable to a wide variety of metal-organic framework materials,and the incorporated materials retained their unique properties.Key factors that affect the extraction efficiency,including the MIL-101(Cr)amount,sample flow rate,type and volume of the eluting solvent,and flow rate of eluting solvent,were investigated.Under optimum conditions,the proposed method exhibited low limits of detection(0.017-0.096 ng mL-1)for six triazines.The relative standard deviations calculated for all herbicides ranged from 0.2 to 14.9%.This method can significantly reduce the amount of organic solvents,and can greatly simplify the pretreatment process of oil matrix samples,with higher extraction efficiency and more convenient operation.A novel vortex-assisted solid-phase extraction method based on MIL-68(Al)/Chitosan-melamine sponge column(or V-MIL-68(Al)/CS-SC-SPE)was designed and developed.The MIL-68(Al)/Chitosan-sponge column was prepared by a simple infiltration method and a preparation process that does not consume organic solvents.Scanning electron microscopy was used to characterize the functionalized sponge columns,and the skeleton and pores of the melamine sponge were successfully modified with the coating material(MIL-68(Al)and chitosan).Chitosan was used successfully not only as an adsorption adjuvant material,but also as an adhesive in the preparation of MIL-68(Al)/CS coating sponge materials.The presented method was further combined with HPLC and used in the determination of trace parabens in environmental water samples.Under the optimum conditions,the method was successfully used to detect the four kinds of parabens in different water samples(domestic water,lake water and river water).The limits of detection ranged between 0.21 and 0.50 ng mL-1,and the relative standard deviations for all parabens were below 10.8%.Melamine sponge was selected as an adsorbed base material in the vortex-assisted SPE to simplify the separation procedures under non-magnetic conditions.And the role of chitosan provides a new direction for the preparation of new functional sponges for detecting contaminants in other complex matrix samples. |
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