Study On Selective Degradation Of Sulfoxaflor In Pu-erh Tea Processing

Objectives:China is a big country of tea production and consumption,and the problem of pesticide residues in tea is attracting more and more attention.There are no clear regulations on the use and limit of four kinds of chiral pesticides,triadimefon,benalaxyl,propiconazole and sulfoxaflor in Pu-erh tea.In order to provide scientific basis for the rational use of four kinds of chiral pesticides in Pu-erh tea,the stability of isomerization and the changes of sulfoxaflor were studied.Methods:The analytical methods of four chiral pesticides,triadimefon,benalaxyl,propiconazole and sulfoxaflor in Pu-erh tea were established by high performance liquid chromatography-tandem mass spectrometry combined with chiral columns,and the pretreatment methods were optimized,the final sample is selected for acetonitrile extraction,and purified by modified QuEChERS method;The chiralpak-IG chiral column and the CAPCELLPAK-C18 column were used in series to separate the four isomers of sulfoxaflor and the stability in methanol,water and acetonitrile solution was investigated;Through the small-scale fermentation and laboratory fermentation experiments of Pu-erh sun-dried green tea and laboratory experiments of fresh tea leaves with different water contents,the changes of sulfoxaflor in the fermentation and sun-dried process were investigated.Results:Triadimefon,benalaxyl,propiconazole and sulfoxaflor showed a good linear relationship in the range of 5 to 1000 ?g/L,the correlation coefficient(R2)?0.991,the detection limit was 1 to 2 ?g/kg,The limit of quantification is 3?6 ?g/kg.Sulfoxaflor will be transformed into achiral enantiomers in methanol and aqueous solution,and can be kept stable in acetonitrile solution,with a conversion rate of<10%in 7 days.Among them,isomer 1 and isomer 4 are converted to each other,and isomer 2 and isomer 3 are converted to each other,the conversion rate in methanol solution is isomer 4>isomer 3>isomer 2>isomer 1.The conversion rate in water isomer 4?isomer 3>isomer 2>isomer 1,and water>methanol.In the experiment of Pu-erh tea fermentation and fresh leaf drying,none of the four isomers of sulfoxaflor was found to be selectively degraded.In the laboratory fermentation process,sulfoxaflor was degraded slowly,and it degraded by 10%to 20%after 18 days of fermentation and sulfoxaflor is rapidly degraded during the fresh leaf drying process,and the content of sulfoxaflor is reduced by 70%?85%.Conclusions:In this study,the analytical methods of chiral isomers of triadimefon,benalaxyl,propiconazole and sulfoxaflor in Pu-erh tea were established,the pretreatment conditions were optimized.By separating the sulfoxaflor isomers,their stability in methanol,water and acetonitrile solvents was investigated.And the selective degradation behavior of sulfoxaflor in the fermentation process of Pu-erh tea and the sun drying process was studied.It can provide an effective and convenient analytical method for the detection of triadimefon,benalaxyl,propiconazole and sulfoxaflor in Pu-erh tea,and it can provide scientific basis for subsequent researches such as the formulation of the safe use limit of sulfoxaflor in Pu-erh tea and the selective environmental behavior of sulfoxaflor.