| Quick,easy,cheap,effective,rugged,and safe method is a simple and straightforward extraction technique that extensively adopted for extracting pesticides from agricultural products.It exhibits the advantages of simple operation,less analysis time,high recovery,less solvent consumption,etc.,which meet the requirement of “green chemistry”.However,a limitation associated with this technique was the matrix-induced signal enhancement effect,which was resulted from the insufficient purification,when it was combined with GC-MS/MS.Furthermore,the usage of little amount of organic solvent would still endanger the health of operators to some extent.In this dissertation,two novel QuEChERS protocols based on materials with green chemistry characteristics,including nitrogen-doped graphite carbon(recycled from industrial waste of dicyandiamide sludge)and natural deep eutectic solvent,were developed and combined with GC-MS/MS for the extraction of organochlorine and pyrethroid pesticides in fruits and vegetables.In addition,the matrix effects of fruits and vegetables on pesticides would seriously affect the accuracy of quantification.Therefore,in this dissertation,the matrix effects of organochlorine and pyrethroid pesticides in the QuEChERS process were systematically studied.The details were as follows:Nitrogen-doped graphite carbon,which was simply prepared from dicyandiamide sludge by calcination and acid wash,was originally used as the sorbent of QuEChERS method.The main experimental parameters which influenced the extraction efficiency and clean-up efficiency,such as types of extraction solvent,types of buffer systems,types and amounts of the sorbents,were optimized.Under the optimal conditions,a modified QuEChERS protocol with nitrogen-doped graphitized carbon as clean-up sorbent was developed to determine 27 organochlorine and pyrethroid pesticides in tomatoes,combining with gas chromatography coupled to tandem mass spectrometry.Compared with the traditional QuEChERS-GC-MS/MS method,higher recoveries and lower matrix effects were obtained by the developed method.In addition,since nitrogen-doped graphite carbon was derived from dicyandiamide sluge,the proposed QuEChERS method exhibited additional advantages of environmental-friendly and low-cost.It could be considered that the proposed method was very promising in pesticides analysis in agricultural products and could be a good alternative for traditional QuEChERS method.Twelve types of hydrophobic natural deep eutectic solvents were prepared by direct heating method,and the structures and thermal stabilities were characterized by NMR,FT-IR and TG.The effects of the types,molar ratios and concentrations of deep eutectic solvents on the GC-MS/MS response of pyrethroids were investigated.Results showed that deep eutectic solvents with lactic acid and decanoic acid as hydrogen bond donor could significantly improve the response and reduce the matrix effect of pyrethroids,indicating that the acid-based deep eutectic solvents could act as an analytical protectant to compensate and eliminate the matrix effect of pyrethroids in GC-MS/MS.Then the extraction efficiencies of pyrethroids using acid-based deep eutectic solvent as QuEChERS extractant were evaluated,the key parameters including types,molar ratios and volumes of deep eutectic solvents were optimized.Under the optimal conditions,a novel QuEChERS-GC-MS/MS method with natural deep eutectic solvent of menthol: decanoic acid(1:1,molar ratio)as both extractant and analytical protectant was developed for determination of seven pyrethroids in tomatoes.Compared with the traditional method,the modified QuEChERS-GC-MS/MS method exhibited higher recoveries(82.7-99.9%),lower matrix effects(6-32%)and less solvent consumption(5 m L).In addition,as menthol: decanoic acid(1:1)is inherently hydrophobic,when it was used as an extractant,phase separation could be easily achieved without the addition of salt,which not only simplifies the operation steps,but also lowers the material costs.Therefore,hydrophobic natural deep eutectic solvent could be a green substitute for acetonitrile in the QuEChERS extraction.The hydrophobic natural deep eutectic solvents-based QuEChERS method exhibited the advantages of effective,economical,non-toxic,safe and environmental-friendly,which provided a new reference for the analysis of pesticide residues in fruits and vegetables.In order to expand the application scope of the new QuEChERS method with menthol: decanoic acid(1:1)as both extractant and analytical protectant,the matrix compensation effects of menthol: decanoic acid(1:1)on organochlorine and pyrethroid pesticides in six fruits and vegetables,including tomatoes,cucumbers,apples,cabbages,eggplants and papayas,were evaluated;and the matrix compensation effects of internal standard addition method were also evaluated.Results showed that when using traditional methods combined with internal standard correction,the matrix effects of pyrethroids cannot be effectively compensated.However,when using the novel method with deep eutectic solvent as protectant combined with internal standard correction,the absolute values of the matrix effects of 27 pesticides were obviously decreased to below 25%,which indicated the method nearly eliminated the matrix effects of pyrethroids between solvent solutions and sample solutions,and demonstrated that deep eutectic solvent of menthol: decanoic acid(1:1)could be used as the analytical protectant of organochlorine and pyrethroid pesticides in tomato,cucumber,apple,cabbage,eggplant and papaya.In addition,the accuracy of quantitative analysis of pyrethroids in different fruits and vegetables calculated by analytical protectant addition method was accessed,and the results were compared with those calculated by the matrix-matched standard solution calibration method.Results showed that the spiked recoveries of seven pyrethroids in 6 kinds of fruits and vegetables were all in the acceptable range of 80-120% when they were calculated by analytical protectant addition method;moreover,the differences between analytical protectant addition method and matrix-matched standard solution calibration method were not significant.It indicated when using the new QuEChERS-GC-MS/MS method to analyze organochlorine and pyrethroid pesticides in fruits and vegetables,it was no need to prepare matrix-matched calibration standards,which offered great convenience for routine daily analysis. |
