Application Of Novel Microextraction Method-Liquid Chromatography-Tandem Mass Spectrometry To The Determination Of Pesticides Residual In Tea

As we all known, China is the biggest country which produces tea leaf in the world. Our tea safety is closely related to the health of people. Therefore, the development of efficient and accurate analytical methods for pesticides residues has become an important and urgent issue for tea security. Before analysis, due to the low or very low concentrations of analytes in tea, together with the complexity of tea matrices, a sample separation and/or a preconcentration technique is required. After purification and extraction of analytes, chromatographic separation and high sensitive detection are performed.Liquid-phase microextraction (LPME) and solid-phase microextraction (SPME) are two newly developed microextraction methods. The advantages of LPME method include little organic solvent consumption and high extraction efficiency. With the development of LPME, there have several different models, for example, single-drop microextraction, dynamic liquid-phase microextraction, hollow-fiber liquid-phase microextraction, dispersive liquid-liquid microextraction (DLLME) and solidification of floating organic-dispersive liquid-liquid microextraction (SFO-DLLME) and so on. The advantages of DLLME and SFO-DLLME methods include not only the merit of LPME but also rapidity, simplicity and low cost. These methods have been widely applied to various fields. In SPME method, sampling, extraction and preconcentration are integrated in a single step. It has developed into various models, such as fiber-SPME, in-tube SPME, stir bar sorptive extraction and monolith-SPME. In which, the monolith based-SPME has been used successfully in sample preparation and preconcentration due to its excellent merits, including little organic solvent consumption, simplicity and ease-to-use.In the present work, three novel sample preparation methods combined with liquid chromatography-tandem mass spectrometry were developed and applied to determine the pesticides residue in tea samples. The main contents of the study are as follows:1. A new dispersive solid-phase extraction (DSPE)-dispersive liquid-liquid microextraction (DLLME) method combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of triazoles pesticides residues in tea. DSPE with C18, primary secondary amine and florisil as sorbents was applied to clean up and minimize the matrix interfere from tea samples, it followed with preconcentration of target compounds in DLLME procedure. The effects of various experimental parameters on DSPE and DLLME procedure were studied systematically, such as the kinds and volume of sorbents, extraction solvent and dispersive solvent, extraction time. Under the optimum conditions, the method was evaluated in tea samples. The matrix-matched calibration curves of three triazoles had good linearity in the range of0.0125-50μg kg-1. The limits of quantification were between4.0and31.6ng kg". The relative standard deviations varied from3.6%to18.6%, respectively. The recoveries in three concentration levels were between91%and118%. The obtained results show that the proposed DSPE-DLLME-LC-MS method is potential for the trace analysis of fungicides in complex sample matrix.2. Dispersive solid-phase extraction (DSPE) and dispersive liquid-liquid microextraction (DLLME-SFO) based on solidification of floating organic drople method was developed for the determination of17pesticides residues in tea. LC-MS/MS was used to determine the multi-residues. In this experiment, multi-walled carbon-nanotubes was selected as sorbent in DSPE,1-dodecanol and ethanol were used as extraction solvent and dispersive solvent, respectively. The salt effect had been investigated. Under the optimum conditions, the method was evaluated in tea samples. The matrix-matched calibration curves of17pesticides had good linearity in the range of0.005-1000μg kg-1. The limits of quantification were between1.0ng kg-1and436.3ng kg-1. The relative standard deviations varied from2.3%to19.0%. The recoveries in three concentration levels were between72%and124%. This method was also applied to determine the multiple pesticides residue in various tea samples.3. Based on a poly (methacrylic acid-co-ethylene glycol dimethacrylate)(MAA-co-EDMA) monolith frit, a novel solid phase-miroextraction (SPME) method combining with liquid chromatography-tandem mass spectrometry was established for analysis of triazoles pesticides residues in tea samples. The monolithic frit was packed into a plastic micro-syringe as a solid support. The polymer monolith was synthesized within the porous polypropylene frit. The effects of various experimental parameters on polymerization conditions, polymer monolith frit solid-phase microextraction and desorption procedure were studied systematically. Under the optimum conditions, the method was evaluated in tea samples. The matrix-matched calibration curves of three triazoles had good linearity in the range of0.01-400μg kg-1. The limits of quantification were between1.0ng kg-1and315.0ng kg-1. The relative standard deviations varied from3.6%to21.3%. The recoveries in three concentration levels were between87%and120%. The proposed method was used for the determination of triazoles residue in tea samples.