A New Method for Residue Determination of Thiamethoxam in Soil

Thiamethoxam{3-(2-chlorothiazol-5-ylmethyl)-5-methyl-4-nitroimino-1,3,5-oxadiazinane}belonging to a new class of insecticides known as neonicotinoids, has been widely used in China and other countries. A new method to analyze the residue of thiamethoxam in soil was established. Residues of thiamethoxam were extracted from soil by methanol in an ultrasonic bath, and cleaned up with a silica gel column, 20 μL of final solution was injected into a C18 reversed-phase column (250 mm×4.6 mm), a mixture of acetonitrile and water at a ratio of 80/20(V/V) as mobile phase. The quantification of the insecticide thiamethoxam was conducted by using UV detection at 254 nm wavelength. The result showed that the average recoveries and coefficient of variations of the method were 78.9%~90.1%, 2.52%~5.67% for soil sample, respectively. The minimum detectable amount of thiamethoxam was 9.6×10-8 g and the minimum detectable concentration of thiamethoxam in the soil samples were 0.024 mg·kg-1. These results showed that the method met the demands of pesticide residue analysis.