Study On The Application Of Accelerated Solvent Extraction And Molecular Imprinting Technology In Pesticide Residue Analysis

In recent years, increasing attention has been paid to the quality and safety (QS) ofproducts and foodstuffs. In the determination of pesticide residues in agricultural productssamples, sample preparation is very important, because the matrix is complicated andconcentration of analyte is very low. It is important to develop fast, efficient, simple andgreen sample preparation method in order to obtain reliable, repeatable analytical result.Accelerated solvent extraction (ASE) is a new green extraction technique. ASE canextract different classes of pesticides residues which exist in numerous kinds of plant originfoods. It possesses many advantages such as easy to operate, less pollution to theenvironment by the organic solvent, less time, less solvent and automatic in the extractionprocedures comparing with other traditional extraction methods. Molecularly imprintedpolymers are specific polymer materials that have the selective binding ability to theparticular molecules. Molecularly imprinted polymers have many advantages of good affinity,high selectivity, powerful anti-interference performance, better stability, as well as long lifeand wide range of applications. Molecular imprinting technology had been used in manyfields such as pesticide residues analysis, food analysis, environmental monitoring, naturalproducts separation and chromatographic analysis. The selectivity of complex samplespretreatment was increased greatly when the accelerated-solvent-extraction technology andmolecularly-imprinted-solid-phase-extraction technology were applied together. And thepesticide residues in complex biological samples can be separated and enriched quickly andeffectively.First of all, it is described that the history and development of the accelerated solventextraction technology and molecularly imprinted technology, and the research advance wasreviewed.In chapter2, a new method for the determination of chlorantraniliprole (CAP) andspirodiclofen (SDF) residues in tobacco was developed by using liquid chromatography withdiode-array detection (LC-DAD) after accelerated solvent extraction (ASE) and silica gel clean-up. The conditions of ASE, silica gel clean-up and LC were investigated and optimized.A Waters C18column (250×4.6mm ID,5μm) was used for the LC using a mobile phasecomposed of methanol and water (90:10, v/v). Under optimal conditions, the linearity wassatisfactory in the range of0.03–1.5μg/mL with a correlation coefficient of0.9994for CAPand0.13–2.5μg/mL with a correlation coefficient of0.9991for SDF. The method limit ofquantification (LOQ) was16.5μg/kg for CAP, and64.3μg/kg for SDF, which is lower thantheir maximum residue limits (MRLs). The recoveries were88.5–102%with relative standarddeviations (RSDs) of2.7–6.9%for CAP, and87.7–98.5%with RSDs of1.8–5.9%for SDF.The proposed method is simple, rapid and effective, and provides the sensitivity and linearitynecessary for analysis of the pesticides in tobacco.In chapter3, a highly sensitive method was developed for the determination of theresidues of cyromazine (CYR) and its metabolite, melamine(MEL), in herbal and edible plantsamples by using reversed phase high-performance liquid chromatography–diode-arraydetection (RP-HPLC-DAD) with accelerated solvent extraction and solid phase extractioncleanup. The conditions of separation and detection were investigated and optimized. AWaters C18column (250x4.6mm，i.d.,5μm) was used for the RP-HPLC, with a mobilephase composed of0.1%trifluoroacetic acid solution and methanol (85:15, v/v, pH2.6).Under the optimized conditions, good linearity was achieved with a correlation coefficient of0.9998. The limits of quantification of the method were2.15μg/kg for CYR and2.51μg/kgfor MEL, which are maximum residue limits as low as three orders of magnitude. Therecovery values at three spiked concentrations were in the range of96.2–107.1%with relativestandard deviations (RSDs) of1.1–5.7%for CYR, and92.7–104.9%with RSDs of1.7–6.1%for MEL. The proposed method allows detection at levels as low as μg/kg levels for CYR andMEL. The method was validated by liquid chromatography–tandem mass spectrometry, andcan be used for the routine determination of CYR and MEL in herbal and edible plantsamples with the characteristics of speed, high sensitivity and accuracy, and low consumptionof reagents. In chapter4, molecular recognition mechanisms for melamine molecularly imprintedpolymers synthesized in ethanol-water system with melamine as template and methacrylicacid as organic functional monomer were examined by the molecular simulation and theexperimental validation with IR and1H NMR. It was found that amino in melamin withcarboxyl group of methacrylic can be combined to be more stable amido goup than hydrogenbond. Binding study demonstrated that the MIPs showed excellent affinity and highselectivity to melamine.In chapter5section1, a highly selective molecularly imprinted solid-phase extraction(MISPE) combined with ultra-performance liquid chromatography-PDA detection wasdeveloped for the simultaneous isolation and determination of cyromazine, melamine,ammeline and ammelide in milk samples. The new melamine molecularly imprintedpolymers (MIPs) was applied as a special sorbent for the selective solid-phase extraction(SPE) of melamine and it’s analogues from milk samples, showing high selectivity andaffinity to the melamine and cyromazine in milk. Used the MIPs as SPE sorbents couldeffectively eliminate the interferences of the milk matrix. Under the optimized conditions,good linearity of the method was obtained in a range of0.013~6.667μg/mL with thecorrelation coefficient of>0.999and the relative standard division of2.0–7.4%. The limits ofquantitation of this method were in a range of1.3ng/mL-6.7ng/mL. The proposed methodcould be applied for the selective extraction, separation and determination of melamine andit’s related compounds in milk samples.In chapter5section2, a highly sensitive method was developed for the determination ofthe residues of cyromazine(CYR), melamine(MEL) anddicyandiamide (DICY) in animaltissue samples by using ultra-high-performance liquid chromatography(UPLC)–PDA eλdetection with accelerated solvent extraction and MISPE cleanup. The conditions ofseparation and detection were investigated and optimized. A ACQUITY UPLC BEH HILIC(100x2.1mm，i.d.,1.7μm) was used for the UPLC, with a mobile phase composed of0.77‰ammonium acetate-acetic acid (pH=4.7) and methanol (4:96, v/v). Under theoptimized conditions, good linearity was achieved with a correlation coefficient of0.9999. The limits of quantification of the method were1.675μg/kg for DICY,5μg/kg for MEL and3.325μg/kg for CYR. The recovery values at three spiked concentrations were in the range of91.2-107%with relative standard deviations (RSDs) of1.7–8.3%for DICY,89.1–105%withRSDs of1.1–6.6%for MEL, and88.7–104%with RSDs of2.1–6.1%for CYR. The proposedmethod can be used for the routine determination of DICY, MEL and CYR in complexbiological samples with the characteristics of high sensitivity, accuracy, and speed.