Study On The Residue Analysis Method Of Four Herbicides Such As Quizalofop-P-Ethyl In Dandelion Tea

Dandelion（Taraxacum mongolicum Hand.-Mazz.）is a perennial herb belonging to the Compositae family.It can be eaten directly from fresh leaves or processed into various dandelion products,such as the leaf of dandelion tea and the root of dandelion tea.Dandelion tea is rich in vitamins and minerals,which plays an important role in human health.In recent years,with the increasing popularity of dandelion tea,the quality of dandelion tea has gradually been valued by people.During the planting process of dandelion,it is necessary to use some herbicides to control the grass weeds,but the subsequent problem is the residue of herbicides on the dandelion,posing a potential risk to the health of dandelion tea drinkers.The article mainly studies and established the residue detection methods of four herbicides（Haloxyfop-P-methyl;Quizalofop-P-ethyl;Fluazifop-P-butyl;Sethoxydim）in two substrates of dandelion leaf tea and root tea,providing scientific basis for the quality and safety evaluation of the four herbicides after use in dandelion field.The specific results are as follows:1.Optimization of mass spectrometry conditions:In order to obtain the optimal detection sensitivity of the four herbicides,a full scan of 0.5 mg/L of the four herbicides standard solutions was performed in the ESI+mode,and the precursor ion peaks of the four herbicides in the ESI+mode.Scanning in SIM mode optimized the intra source fragmentation voltages of the four herbicides,followed by product ion scanning,and selected two product ions with strong abundance,high response values,and little mutual interference as qualitative and quantitative ions for the four herbicides.The collision energy of the product ions was optimized to ensure the sensitivity and reproducibility of various herbicides.2.Optimization of chromatographic conditions:Under the same gradient elution conditions,the effects of four mobile phase conditions,namely,a:acetonitrile-pure water,b:acetonitrile-pure water containing 0.1%formic acid,c:acetonitrile-pure water containing 5mmol/L ammonium acetate,and d:acetonitrile-pure water containing 0.1%formic acid+5mmol/L ammonium acetate,the peak shapes of the four herbicides were sharper,The highest response value was obtained,d:acetonitrile-pure water obtaining 0.1%formic acid+5 mmol/L ammonium acetate was selected as the mobile phase for this method.3.Optimization of extraction solution:The extraction efficiency of methanol,ethyl acetate,acetone,acetonitrile,0.1%formic acetonitrile,0.2%formic acetonitrile,and 0.3%formic acetonitrile for four herbicides in dandelion tea was compared.The results showed that the extraction efficiencies of the four herbicides in dandelion tea were acetonitrile（92.4%～105.5%）,0.1%formic acetonitrile（88.5%～96.%）,0.2%formic acetonitrile（97.7%～102.6%）,0.3%formic acetonitrile（62.4%～91.2%）,ethyl acetate（104.1%～119.3%）,methanol（77.4%～139.0%）,and acetone（77.2%～120.9%）,respectively.Therefore,0.2%formic acid acetonitrile was selected as the extraction agent.Subsequently,the extraction efficiency of 5 mL,10 mL of water,and 20 mL 0.2%formic acetonitrile for dandelion tea was investigated,with recoveries of 96.9%to 99.3%and 105.7%to 122.2%.Therefore,5 mL of water immersion matrix was selected for extraction.The effect of 10 mL,15 mL,and 20 mL of 0.2%formic acetonitrile+5mL of water on the recovery rate was optimized.the recovery rates were 84.7%～106.2%,94.2%～106.1%,and 97.5%～107.9%,respectively.Therefore,5 mL of water and 20 mL of 0.2%formic acetonitrile were selected as the extraction solvents for this experiment,which met the residue detection standards and had significant purification effects on pigments.4.Optimization of purification agent:PSA,C₁₈ and GCB,three traditional QuEChERS purification materials,are combined to form different purification agent combinations,and the combination with the best purification effect is selected.The results showed that for root of dandelion tea,the combination of 50 mg C₁₈+80 mg PSA+150 mg anhydrous magnesium sulfate had the best purification effect,with a recovery rate of 93.4%～105.0%;For leaf of dandelion tea,the combination of 30 mg PSA+80 mg C₁₈+20 mg GCB+150 mg anhydrous magnesium sulfate has the best purification effect,with the recovery rate of 87.8%～101.4%.The reason for increasing the amount of GCB is that the pigment content of leaf of dandelion tea is large,and increasing the GCB content significantly reduced the impact of the pigment on the extraction efficiency,and GCB has a strong adsorption capacity for the Haloxyfop-P-methyl,with a significantly decrease in the recovery rate when increasing to 30 mg.Therefore,the dosage f GCB is selected as 20 mg purifying the leaf of dandelion tea.5.Method validation:The method established in this paper is verified.The results showed that the four herbicides showed very good linearity in the standard curve of different matrix matching,r was greater than 0.995;According to the minimum addition level,the limit of quantification（LOQ）of four herbicides in root of dandelion tea and leaf of dandelion tea is 0.01mg/kg;Under the conditions of three added concentrations（0.01 mg/kg,0.1 mg/kg,1.0 mg/kg）,the added recoveries of the four herbicides in root of dandelion tea are 93.4%～105.0%,the relative standard deviation（RSD）is 0.7%～3.3%,and the added recoveries in leaf of dandelion tea are 87.8%～101.4%,and the relative standard deviation（RSD）is 0.4%～5.0%.It can be seen that the accuracy and precision of the method meet the requirements of pesticide residue analysis.