Research On Intelligent Extraction Method Based On Poly (N-isopropylacrylamide) Sensitivity

Polyisopropylacrylamide（PNIPAM）is a temperature and acidity sensitive polymer which has three types including linear polymer,covalently cross-linked polymer and surface grafted material.Linear polymers with isopropylacrylamide（NIPAM）as a monomer are hydrophilic and soluble in water at temperatures below their low critical phase transition temperature（LCST）.When the solution temperature is higher than the LCST,PNIPAM is hydrophobic and precipitates from the aqueous solution.Adjusting the temperature allows reversible dissolution and precipitation of this polymer in aqueous solution.The NIPAM covalently cross-linked polymer has acidity sensitivity,and changing the pH can adjust its degree of swelling and pore size,thus affecting its adsorption properties.This research established a new method of phase transition dispersive extraction（PTDE）and in tube solid-phase microextraction based on the sensitive characteristics of PNIPAM linear polymer and covalently cross-linked polymer,respectively.The main contents are as follows:Synthesized PNIPAM linear polymer and established a new phase transition dispersive extraction based on its temperature sensitivity.PNIPAM was dissolved in the sample solution below the LCST,and PNIPAM was dissolved in water as a linear polymer to adsorb2-naphthol in the solution through hydrogen bonding and hydrophobic effects.When the solution is heated to a temperature higher than the LCST,PNIPAM molecules curl,precipitate,and encapsulate 2-naphthol,assisted by the salting out effect.Then redissolve the precipitated PNIPAM in a small volume of water whose temperature is below the LCST,causing separation and enrichment of 2-naphthol.The PTDE method greatly improved the dispersity of materials in dispersive extraction,which replaced centrifugation with temperature triggered liquid-solid separation and simplified the extraction separation process,meanwhile,in the extraction and desorption processes,no organic solvents were used.Thermogravimetric analysis indicated that PNIPAM has good thermal stability.Infrared spectroscopic analysis showed that the wavelength of IR characteristic peaks changed before and after PNIPAM adsorbed 2-naphthol,verifying the hydrogen bonding and hydrophobic interaction between PNIPAM and 2-naphthol.An analytical method（PTDE-HPLC-UV）for the determination of2-naphthol residues in citrus was established under the optimized conditions of sample solution acidity,ionic strength,stirring time and speed.The linear range of this method was0.4-1000μg·kg^-1（R²=0.9996）,the detection limit（LOD,S/N=3）was 0.12μg·kg^-1,and the recovery was 97.1%-101.3%,the enrichment factor was 90.9.The NIPAM covalently cross-linked polymer monolithic column（P-NIPAM-MAA-co-DVB）was prepared under optimized synthetic conditions using NIPAM and methacrylic acid（MAA）as dual monomers,p-diethylene benzene（DVB）as cross linker,and AIBN as initiator,and was applied to solid-phase microextraction（SPME）.The NIPAM co monolithic column was characterized by SEM,FT-IR,TGA and nitrogen adsorption desorption experiments.The characterization results showed that the NIPAM copolymerized monolith was synthesized successfully with a specific surface area of 266.6 m²·g^-1,which exhibited good thermal stability and moreover,the framework to pore bicontinuous structure characteristic of monolith.Comparative experiments showed that MAA in monolithic column effectively improved the stability in alkaline environment of this material.The copolymerization monolithic column enabled the simultaneous adsorption of phenolics with polycyclic aromatic hydrocarbons such as fluorene,phenanthrene,and fluoranthene in a weak acid environment.When eluted with a strong base solution,phenolics ionized while their solubility in water increased,meanwhile the hydrogen bonding interactions between phenolic compounds and the monolithic column were disrupted.Therefore,phenolic compounds were effectively eluted,while polycyclic aromatic hydrocarbons compounds combined with polymer monoliths mainly in hydrophobic interaction andπ-πaction were not easily eluted by basic solution,thus achieving the effective elution of phenolic compounds and achieving the effect of secondary separation.The method was linear in the range of 1.0-200μg·L^-1for p-phenol,m-cresol,and o-nitrophenol,0.3μg·L^-1for p-nitrophenol,2,4-dichlorophenol,and p-tert-butylphenol.The intra and inter day precisions（RSDs）were less than 9.8%.The spiked recoveries were in the range of 86.3%-114.1%.