| Tea is rich in nutrients,and China has been trading with many countries and regions.Due to the increasingly strict restrictions on pesticide residues in tea in developed countries and regions such as the European Union and Japan,China’s tea exports have also been greatly affected.At present,the level of pesticide residue analysis and detection technology in China is relatively lagging.The pre-processing operation of the national standard method is complicated and takes a long time.The extraction and purification process requires the use of more organic reagents.The detection instruments are expensive and not universal.Therefore,this paper takes dicofol and fenvalerate in tea as research objects,and studies the pretreatment methods and detection techniques of tea samples to meet the detection requirements of two pesticide residues in tea in different grassroots laboratories.The main findings of this project are as follows:A pretreatment method for multi-walled carbon nanotube-dispersion solid phase extraction was studied.The recovery rate of the two pesticides was optimized,and the extraction solvent,solid-liquid ratio,PSA and MWCNTs were optimized by single factor test and orthogonal test.The results showed that the optimal pretreatment conditions were acetonitrile(1% acetic acid)as the extraction solvent,the ratio of material to liquid was 1:4,the amount of PSA was 150 mg,and the amount of multi-walled carbon nanotubes was 250 mg.The optimized pretreatment conditions were tested using three different types of fermented teas: green tea,green tea and black tea.The recoveries of the two pesticides were between 92.50% and 104.17%.The method has high accuracy and is applicable.Detection of two pesticide residues in three types of tea.Based on the national standard(GB/T 23204-2008),the chromatographic conditions of gas chromatography-mass spectrometry were optimized and combined with multi-walled carbon nanotube-dispersion solid phase extraction pretreatment method for method validation.The calibration curve was prepared by adding the blank tea sample matrix to reduce the matrix interference.The two pesticides were in the linear range of 0.02 μg/mL~1 μg/mL,and the detection limit was 0.004 mg/kg~0.010 mg/kg.The limit of quantification was 0.016 mg/kg~0.038 mg/kg,the recovery rate was 90.74%~99.58% and the RSD was 1.61%~5.41% under the three spiked concentrations,which met the requirements for pesticide residue detection in tea.In this paper,a gas chromatography method based on multi-walled carbon nanotubedispersion solid phase extraction as a pretreatment method was established with reference to relevant literature.Methodologically verified: the two pesticides have a good linear range from 0.02 μg/mL to 1 μg/mL,r>0.999,the detection limit is 0.008 mg/kg~0.014 mg/kg,and the limit of quantification is 0.025 mg/kg~0.042 mg/kg,the recoveries were 85.03%~93.03% and the RSD was 1.01%~5.90% under the three spiked concentrations,indicating that the analytical method has good separation effect and accurate and reliable results.By comparing the multi-walled carbon nanotube-dispersion solid phase extraction/GCMS method,multi-walled carbon nanotube-dispersion solid phase extraction/GC method and the national standard method studied in this paper,multi-walled carbon nanotubes-dispersed The GC-MS method after pre-solid phase extraction has the advantages of time saving,less organic solvent,simple operation,low cost,fast analysis time,low detection limit and high sensitivity.Compared with the national standard method,the new GC method is compared with the national standard method.The linear range,the detection limit and the recovery rate all meet the testing requirements of the national standard,and the stability of the method is good,the instrument is cheap,and the popularity is high,which can be applied to the promotion of basic laboratory. |
