A Novel Extraction Method And Its Application To The Analysis Of Pesticide Residues In Tea Samples

Food is the material basis for human survival and development, food safety problem is not only the most basic quality requirements, but also the major problem related to people’s health. The analys is of pesticide residues in food samples has received increasing attention in the last few decades, there are strict regulations about maximum residue limits (MRLs) of pesticides in food established by several international organizations and countries. Multi-pesticides residues in food matrix are difficult to analyze due to the very low amounts, the complexity of the sample matrices and many interfering substances coexisting. Therefore, it is of significance to develop rapid, simple, and effective methods for the analysis of trace-level multi-residue pesticides in food samples.In recent years, solid phase extraction and liquid phase microextraction have attracted considerable attention due to the advantages of reduction of organic solvent, shortening the extraction time and high extraction effectivity, and they have been applied widely to the analysis of multi-pesticide residues in different sample matrices. Based on these, a lot of new types of sample preparation techniques are developed, such as molecularly imprinted solid-phase extraction, magnetic solid-phase extraction, dispersive solid phase extraction and dispersive liquid-liquid microextraction. Molecularly imprinted polymers present a number of advantages including ease of preparation, high thermal and chemical stability and high selectivity, these makes them very attractive metrials as SPE sorbents. In ispersive solid phase extraction, sorbents are dispersed into sample solutions and used for absorb interfering substances, and this method is used for multi-residue analysis of pesticides in food samples. These methods have their own advandages, and have been widely applied in medicine, food and environmental fields and so on.In our research, three novel sample preparation methods are developed and have been used for the analysis of multi-pesticides residues in tea samples combining with high performance liquid chromatography-tandem mass spectrometry. The main study contents are listed as follows:1. Based on molecularly imprinted polymers, a molecularly imprinted solid-phase extraction (MISPE) method was developed for selective extraction and analysis of triazine herbicides residues in tea samples by coupling to LC-MS/MS. A molecularly imprinted polymer with propazine as template was synthesized and used as solid phase extraction sorbents. The infrared spectra (IR), selectivity and thermal stability properties of the MIP were characterized, and a series of experimental parameters were optimized systematically. Under optimized conditions, the detection limit (LOD) of0.2ng kg-1were obtained, the average recoveries for five triazine herbicides were in the range of75-137%. The simple, selective, sensitive and effective method was successfully applied for the determination of five triazines in seven real tea samples.2. A novel extraction technique by combining the dispersive liquid-liquid microextraction (DLLME) and magnetic solid-phase extraction (MSPE) was developed for the analysis of multi-pesticides residues in tea samples. In DLLME, a low-density organic solvent (1-octanol) was selected as extraction solvent, and no disperser solvent was used. The hydrophobic magnetic nanoparticles were synthesized and utilized to adsorb1-octanol in MSPE. The parameters that affect extraction and desorption were optimized systematically. The intra-and inter-day relative standard deviations (RSDs, n=6) were2.3-8.5%and5.3-12.4%, respectively. The calibration curves of analytes showed good linearity in the range of0.05-100μg kg-1. The average recoveries for multi-pesticides residues were in the range of70-109%. These satisfactory results demonstrated that the developed method is reliable for the analysis of trace multi-pesticides residues in tea samples.3. A multi-residue method based on modified QuEChERS sample preparation was developed for analysis of multi-pesticides residues in tea samples by LC-MS/MS. Tea sample preparation utilized a modified QuEChERS method with acetonitrile as extraction solvent followed by sample cleanup using C18sorbent and multi-walled carbon nanotubes (MWCNTs). The parameters that affect sample preparation and cleanup were optimized systematically. Under the optimized conditions, the basic analytical parameters including linearity (r>0.9985), limit of detection (LOD≤18.4ng kg-1), precision (RSD≤12.6%) and recovery (R=71-116%) were evaluated in tea matrix. Finally, the QuEChERS method was successfully applied for the determination of eighteen pesticide residues in tea samples by coupling to liquid chromatography-tandem mass spectrometry.