Study On Molecular Design And Mechanism Of Complex Extractants Containing Ionic Liquids For Microextraction Phoxim

DLLME as a detection method is widely used in organophosphorus pesticides.However,traditional DLLME often use toxic extractants such as haloalkanes,which cause some harm to the environment.Ionic liquids as an environmentally solvents and its superior solubility are widly used in DLLME.Due to the larger cationic structure of the ionic liquid,the viscosity of the ionic liquid is relatively large,which reduces the extraction performance of the ionic liquid extractant.In response to these problems,this paper presents a new extractant-composite extractant composed of ionic liquid and molecular solvent.Adding a small amount of molecular solvent can greatly reduce the viscosity of ILs.At the same time,suitable molecular solvents can not only be used as viscosity reducing agents,but also can be used in extraction.Because there are many types of ionic liquids,it is very important to choose suitable ionic liquids as the extraction agent,and it is also very important to choose suitable molecular solvents to improve the extraction capacity.The content of this article is as follows:1.The molecular connectivity index method was used to calculate the polar indices of different ionic liquids and phoxim,using the closeness of the polarity index between the ILs and phoxim,then combining the actual conditions to select the appropriate ionic liquid extractant as[HMIM][PF₆],and the COSMO-SAC model was used to verify the reliability of the selected ILs.2.According to the factors such as density,miscibility,extraction performance and molecular connectivity index method,four molecular solvents such as chlorobenzene,trichloromethane,butyl acetate and hexyl acetate were preliminarily selected.Through density density function theory,the influence of four molecular solvents on ionic liquids was explored.The study show that the addition of molecular solvent increases the length of the hydrogen bond between cation and anion in the ILs,the order is butyl acetate>hexyl acetate>Chlorobenzene>Chloroform;The addition of molecular solvent can transfer the charge between the anions and cations of the ionic liquid,which will reduce the hydrogen bonds formed between the cation and the fluorine atom to some extent.The order of the four solvents was hexyl acetate>butyl acetate>chloroform>chlorobenzene;Computation and analysis of the interaction energies of the composite system show that the mutual energy between esters and ionic liquids is the largest,the esters has the greatest influence on the interaction between anions and cations of ionic liquids.According to the configuration and charge analysis,it can be seen that the addition of the two esters can reduce the interaction between the anionic and cationic ions of the ionic liquid,which in turn leads to a decrease in the viscosity of the ionic liquid.Since the water solubility of butyl acetate is greater than that of hexyl acetate,it is not conducive to the extraction.Therefore,the hexyl acetate was selectedas the compound extractant with ionic liquid.At last,the extraction mechanism of the composite extractant was discussed to prove that the compound extractant can effectively improve the extraction effect.3.Ultrasound-assisted compound extractants were combined with HPLC to disperse phoxim in water samples.Experiments have shown that the addition of a small amount of molecular solvent can improve the extraction efficiency of ionic liquids.The optimized experimental conditions were as follows:water volume 8 mL,compound ratio（ILs:hexyl acetate）was 70μL:30μL,sonication for 15 min,ice bath for 25 min.Under this operating condition,there was a good linear relationship between phoxim in the linear range of1-500μg/L,relative standard deviation of 2.9%and detection limit of 0.18μg/L.The method has the advantages of simple operation,high enrichment rate,high recovery rate,low cost,and use of a low-toxicity extractant,it also reduced the harm to the environment.