Determination And Degradation Of Imidacloprid Residue In Tea And Soil

This paper reported the method of determination of residual imidacloprid in tea and soil by HPLC. Imidacloprid was extracted with an ultrasonic bath by methylalcohol, and then reextracted by dichloromethane, cleaned up by Florisil column and Na₂SO₄, eluted with mixture of petroleum ether:ethyi(95:5,V/V), petroleumether:ethyi(3:1,V/V). Imidacloprid could be detected by HPLC technique and a good chromatographic separation. The minimum amount of detection was 1.0× 10^-9g. The detectable limit of concentration was 0.01mg/kg. The average recovery of imidacloprid and variation coefficient was 80.56%-90.01% and 0.29% -3.46%, respectively.Residual trial of 70% imidacloprid were conducted at FAFU. The result showed that under applied level of 80g/hm², the half-life of imidacloprid was 5.05 days in tea leaves and 9.49 days in soil.Tea were treated one and two times and interval of 7 days with the dosages of 40g/hm² and 80g/hm² during the growing season of tea. The residue of imidacloprid on tea were <0. 01mg.kg^-1-0. 903mg.kg^-1 in soil were 0. 074mg.kg^-1-0. 318mg.kg^-1 after the last application 7, 21days. There were positive relation between residue and amount as well as times sprays for, and negative relation residue and the days from last application to harvest.Imidacloprid is a nicotinic insecticides. Our government has not formulated the rules of application and MRL on tea. Based on the result of the trial and reference to foreign MRL, we suggest that the dosages of Imidacloprid applied on tea be 40g/hm² and one time during the tea growing period, secure interval time be 21 days and MRL be 0.01mg.kg^-1 in tea.