Covalent Organic Framework TpBD For Solid Phase (Micro-) Extraction Of Phthalate Esters In Food

Phthalate esters（PAEs）are commonly used as plasticizers to increase the flexibility,transparency and longevity of plastics.Since PAEs are physically bonded to the polymer matrix rather than chemically bonded,they are easily migrated from food packaging to food.In addition,PAEs can be released into the environment during manufacture,application,and handling,and absorbed into the food chain by plants and animals.Because of the potential carcinogenicity and developmental toxicity,many countries have established limits on PAEs in food.Therefore,it is of great significance to establish pre-enrichment and trace determintion methods for PAEs in food.Covalent organic frameworks（COFs）are a new type of porous material with adjustable pore size,large specific surface area,good thermal stability and chemical stability,which makes COFs have good application prospects in the field of separation.In this paper,the magnetic solid phase extraction（MSPE）adsorbent TpBD/Fe₃O₄and solid phase microextraction（SPME）fiber TpBD-TiO₂ coating were prepared.Taking PAES as the research object,the separation and enrichment pretreatment methods was establish based on solid phase（micro）extraction.And then,the pretreatment methods were combined with GC-MS/MS to determine a variety of PAEs in eight kinds of beverages and three greenhouse vegetables.The main studies and results are as follows:（1）The magnetic covalent organic framework material TpBD/Fe₃O₄ was synthesized by a facile co-precipitation method.The material was used as MSPE adsorbent and combined with GC-MS/MS technology to establish a method for the determination of 15 PAEs,which was applied to the determination of beverage samples.The crystal structure,molecular structure,element distribution,morphology and magnetization of TpBD/Fe₃O₄ were characterized by X-ray Diffraction（XRD）,Fourier Transform Infrared Spectroscopy（FT-IR）,Energy Dispersive X-Ray Spectroscopy（EDX）,Transmission Electron Microscopy（TEM）and Vibrating Sample Magnetometer（VSM）.A new method for the determination of 15 PAEs in eight beverages by MSPE-GC-MS/MS was established by optimizing extraction time,elution time,adsorbent dosage,ionic strength,desorption solvent and desorption volume.The limits of detection（LODs）of this method is 0.005-2.748μg/L（signal-to-noise ratio S/N=3）.The intra-and inter-day relative standard deviation（RSDs）values were less than 8.8%and 9.9%,respectively.The prepared adsorbent can be reused after washing with methanol.The method has been successfully applied to the determination of PAEs in kinds of beverages,and the recoveries are 79.8%-121.8%,and the RSDs are less than 11.9%.This work provides a simple（one-step）,fast（30 min）magnetization method for COFs that can be applied to the enrichment and separation of PAEs in beverage samples from different matrices.（2）Titanium wire was selected as the substrate of the solid phase microextraction（SPME）fiber,and TiO₂ nanotube arrays were formed on the surface of the fibers by electrochemical anodic oxidation,with Ti-OH groups provided at the same time.Ti-OH groups were modified into amino groups by APTES,then COF material TpBD was covalently bonded to titanium wire by in-situ growth method to prepare TpBD-TiO₂ coated SPME fiber.A trace detection method for 11 PAEs was established by TpBD-TiO₂ fiber-GC-MS/MS,and the SPME fiber was used for headspace extraction of trace amounts of PAEs in vegetables.The crystal form,molecular structure,morphology and specific surface area of the composite COF TpBD-TiO₂were characterized by XRD,FT-IR,Scanning Electron Microscopy（SEM）and N₂ adsorption.The extraction time and temperature,desorption time and temperature,and ionic strength conditions were optimized.The enrichment factor（EF）and lifetime of the solid phase microextraction fibers were also investigated.The EF is between 226 and 2154,and the enrichment effect can still retain more than 95.2%of the first use effect when the number of uses exceeds 150 times.The limits of detection of this method was 0.001-0.188μg/L（S/N=3）,and the RSDs between single needle and needle-to-needle were less than 9.4%and 10.8%,respectively.Quantitative determination of PAEs in vegetable samples（tomato,lettuce,cucumber）was achieved by standard addition.