| Tea from China to the world has become one of the world's most popular drinks.After tea is brewed with boiling water,it has a fragrant odor.It can improve the health of your bones,reduce obesity,delay aging,and prevent cardiovascular diseases.Different types of pesticides are used in the cultivation of tea plants,of which the most widely used are organophosphorus pesticides(OPPs).Due to a large number of applications or improper methods of use,some pesticide residues in tea will inevitably occur,posing a potential threat to the health of tea drinkers.In view of this,all countries in the world have introduced relevant regulations in order to limit the maximum residue limit of such pesticides and seriously affect China's tea export trade.In response to this problem,this paper used tea matrix and tea broth matrix as the research substrate,Five organophosphorus pesticides(dichlorvos,dimethoate,chlorpyrifos,isocarbophos,and triazophos)with a wide range of applications were selected.The combined use of modified QuEChERS-GC-FPD and DLLME-GC-FPD was established.The results of the study are as follows:The paper improved the traditional QuEChERS method,selected PSA,GCB,Fe3O4,MWCNTs as a new scavenger combination to replace the traditional scavenger,and determined that 2.0 mL of acetonitrile,40 mg NaCl,40 mg Trisodium citrate dihydrate,20 mg disodium citrate sesquihydrate was needed for every 0.50 g of tea sample.For each 1.0 mL extract,a combination of 40 mg NaCl,150 mg anhydrous magnesium sulfate,25 mg PSA,7.5 mg GCB,30 mg Fe3O4 nanoparticles,and 15 mg MWCNTs was added.The recoveries of the five organophosphorus pesticides in the blank tea samples obtained by this method ranged from 80%to 108.3%with relative standard deviations of 2.58%to 7.31%,which met the detection of pesticide residues in tea import and export.Agilent 6890N(FPD)gas chromatograph was used to analyze the residual organophosphorus pesticides in tea samples.Optimize the gas chromatographic detection conditions,and finally select 350? as the optimum injection port temperature.The optimal carrier gas flow rate is 0.2 mL/min,and the injection volume is 1?L without splitting injection.Using retention time qualitative,matrix external standard method.At the same time,the situation of target interference by the matrix was analyzed and studied.The blank matrix extract was used to prepare the standard solution to eliminate the matrix effect.The five organophosphorus pesticides had a good linearity in the range of 0.5?200 pg/L.The correlation coefficients were all greater than 0.998.The detection limits were between 0.608 and 4.420 ?g/kg,and the limits of quantitation were between 3.448 and 10.736 ?g/kg.In the study of the tea soup base system,the blank tea was spiked and the tea was brewed by boiling water to obtain the labeled tea soup to simulate the real sample.It was determined that the five kinds of OPPs to be tested could be maximized when the brewing time was 10 minutes.The DLLME method was used to extract and enrich the tea broth system,and the optimization results showed that every 5 mL of tea broth required 60 ?L of chlorobenzene and 800 ?L of acetone as dispersant to form three-phase milk in the aqueous phase.The detection limits of the five organophosphorus pesticides in the tea soup determined by this method were between 0.026 and 0.794 ?g/L,and the enrichment factor was between 178 and 435.The RSD values of the retention time and peak area were lower than 0.58%and 5.18%,respectively,while the RSD values of the retention time and peak area were less than 1.42%and 7.28%,respectively.The average recoveries of the five OPPs ranged from 83.75%to 103.08%,and the RSD ranged from 2.74%to 7.68%,both of which met the pesticide residue testing requirements.The real samples of 10 tea samples commercially available in Wuhan were spot-checked by the two established methods,and the QuEChERS pretreatment method was used to determine the tea substrate matrix system and the DLLME pretreatment method to determine the target residue detection results of the tea matrix system.The test results for the same batch of tea samples were basically consistent,and the residuals detected were all below the maximum residue limit of the national standard.The pesticide residues in the tea broth were less than about ten times the pesticide residues in the tea.The results of sample pretreatment and analysis directly on the tea soup show that this method is closer to the actual scene of life and has more practical significance.It meets the requirements for detection and analysis of pesticide residues in tea. |
PDF Full Text Request