Application Of Cucurbiturils Matrix Solid Phase Dispersion Extraction In Food Analysis

Matrix Solid-Phase Dispersion(MSPD)is a pretreatment method suitable for solid,semi-solid,and viscous samples.Its working principle is to add the dispersant directly to the sample,grind it evenly,and then install the column.Different elution solvents elute the sample column to finally elute the target analyte.Because of its outstanding advantages such as simple operation method,low cost,small amount of organic solvent and strong versatility,it has been widely used in trace analysis of pesticide residues in food in recent years.Cucurbiturils(Q[n])has unique molecular recognition ability and good thermal stability due to its unique structure.Therefore,in this experiment,a matrix solid phase dispersion extraction method with Cucurbit[7]urils as a dispersant was established,and high-performance phase liquid chromatography(HPLC)was used as a detection instrument.The four bipyridyl cationic herbicides(diquat,methyl(Purple essence,ethyl amethyst,wild swallow)were separated and detected.The main research contents are as follows:In Introduction,mainly introduces the hazards of pesticide residues in food;pesticide residue detection technology in food;pretreatment methods for pesticide residue detection in food;Principle of matrix solid phase dispersion(MSPD),effect of dispersant on MSPD method and application of MSPD method in pesticide residue;concept and research progress of Cucurbiturils.In Chapter 2,the crude product mixture containing a large amount of Cucurbit[7]urils(Q[7])is separated and purified by column chromatography.Use silica gel thin layer chromatography to track the composition changes of the eluent,collect Q[7]solution,spin to concentrate and precipitate with methanol,wash and filter with acetone,and dry under infrared lamp to obtain pure Q[7],and use ~1HNMR.characterization.To establish an analytical method for the determination of four bipyridyl cationic herbicides(Diquat?Paraquat?Ethyl viologen?Difenzoquat)residues in vegetables using Cucurbit[7]urils(Q[7])as a dispersant,matrix solid phase dispersion extraction and high performance liquid chromatography.Chromatographic conditions(detection wavelength,mobile phase and elution gradient)and pretreatment conditions(grinding time,ratio of dispersant to sample,type and amount of eluent,type and amount of eluent,eluent elution Speed)related experimental parameters are optimized,and the central composite design/response surface method is used to investigate the four factors of the optimized amount of eluent,the ratio of sample to Q[7]mass and the grinding time.The final optimal chromatographic conditions were determined as follows:the mobile phase consisted of acetonitrile(A)and a buffer solution containing0.1 mmol/L potassium dihydrogen phosphate(adjusted PH=2.5)containing 56 mmol/L sodium heptane(B).The stripping procedure is 0?18 min 88%B;18?40 min 65%B,the flow rate is 1 mL/min,the detection wavelength is 257 nm,and the injection volume is 20?L.The best pretreatment condition is:the mass ratio of vegetable sample to Q[7]is 1:1,20 mL of n-hexane:ethyl acetate:acetone(v/v 1:1:1)as eluent,5 m L Methanol containing 2%formic acid as eluent,and elutes at a rate of 5 s/drop.The best experimental conditions of the four factors obtained by the central composite design/response surface method are:amount of eluent 5.42?6.13 mL,mass ratio of sample to Q[7]206.07?217.07 mg,grinding time 4.98?5.61 min.Under the best experimental conditions,the measured linear range is 1?100?g/kg,the correlation coefficient(R~2)is between 0.9822?0.9875,and the detection limits and quantification limits of the four bipyridyl cationic herbicides are 0.031?0.288?g/kg and 0.102?0.961?g/kg.The method was applied to the actual samples of 8 vegetables(lettuce,cucumber,tomato,potato,sweet potato,cabbage,Chinese cabbage,pepper).The results showed that no Paraquat was detected in all vegetables.Ethyl viologen and difenzoquat were detected;diquat was detected in potato samples;Ethyl viologen,diquat and difenzoquat were detected in cucumber samples.8 kinds of vegetable samples were recovered at three concentration levels of 1?g/kg,10?g/kg,and 100?g/kg.The recovery rate of the4 pesticides in 8 kinds of vegetables was between 68.90%and 114.61%,The relative standard deviation(RSD)is 2.1%?9.0%.Experimental results show that this method can meet the trace analysis of pesticide residues in vegetables,and its detection limit is lower than the EU standard for maximum residues of pesticide residues in vegetables.At the same time,under the optimal conditions,the comparison effect between Q[7]and other common dispersants(silica gel,diatomaceous earth,magnesium silicate,neutral alumina)in MSPD method was investigated.The results showed that except magnesium silicate for the recovery of target analytes The rate is similar to Q[7],the recovery rate of the remaining three dispersants to the target analyte is very different from Q[7],and through chromatogram comparison,it can be found that Q[7]is more chromatographic than the other four dispersants.Cleaner,less impurity interference and good peak shape of each target analyte.In Chapter 3,the isothermal titration calorimetry(ITC)was used to examine the interaction between the Cucurbit[7]urils and the four bipyridyl cationic herbicides,diquat,methyl viologen,ethyl viologen and wild swallow.effect.Experiments show that the binding constants(Ka)of Q[7]and four bipyridyl cationic herbicides are3.216×10~5,4.399×10~6,6.523×10~6,and 6.556×10~6,respectively,and the number of binding sites(n)is approximately equal to 1.In summary,Q[7]has a strong binding ability with 4 bipyridyl cationic herbicides,and Q[7]has a good molecular recognition ability for 4 bipyridyl cationic herbicides,which serves as a retention target The role of the analyte.