| Tobacco is an important economic crop. But the pests and diseases are important factors which affect our country's tobacco production and quality. As a result of extensive, substantial and long-term use of chemical pesticides in tobacco, the residues of pesticide in tobacco increases, and the insecticide resistance become more and more strong, All these mean "Three R" (Residue, Resistance, Resurgence) problem. In late years, because people enjoy a lot of vegetables, fruits and other food which have excessive pesticide residues, the pesticide poisoning incidents become increasingly frequent. In addition, in the current international trade, many developed countries take the pesticide residual limitations for warrant to conform to the WTO/SPS agreement, and set up technical barriers to trade, which has seriously affected the agricultural products' international trade in China. Therefore, for protecting of consumers' health, eliminating the technical barriers of China's agricultural exports and enhancing China's competitiveness in the international market of agricultural products, the issue of pesticide residues in tobacco causes the entire society's attention.Dimethachlon is a dicarboximides fungicide with low toxicity and high effectiveness. It is effective for Sclerotinia sclerotiorum, Alternaria alternate, Rhizoctonia cerealis and so on. It is necessary to develop a fast, exact and sensitive screening method to monitor levels of dimethachlon residue. In this paper, a method for determination of Dimethachlon in tobacco by high-performance liquid chromatography (HPLC) was proposed. The residual Dimethachlon in sample was extracted with acetonitrile, and purfied with florisil solid-phase extraction (SPE) column. After then it was analyzed with HPLC. In detail, the detection wavelength was 251 nm, the chromatography column was Kromasil C18 250mm*4.6mm*5μm and the mobile phase was 85%(V/V) acetonitrile aqueous solution, the flow was 0.80 mL/min.The results showed that the linear dynamic ranges of detection were 0.05-50μg/mL. The correlation coefficient was 0.9999. The limit of detection (LOD) of Dimethachlon was 0.01μg/mL. The average recoveries of Dimethachlon ranged 65.93% to 96.90%, when the added concentration of Dimethachlon ranged 0.05 to 10μg/mL. The relative standard deviations were in range of 1.10%～5.90%, The within-run relative standard deviations were less than 1.5%, the non-linear regression equation between Dimethachlon additive concentration and average recovery was applied. This results indicated that this method is easier, faster, sensitive and higher recovery than the results by Gas Chromatography. The method we developed in this paper can be applied to determine the residual Dimethachlon in tobacco.In order to evaluate the safety of dimethachlon to tobacco, offer rational drug use plan, and provide a scientific basis for widely use of Dimethachlon on agricultural crops. In this paper, we studied the dynamic and final residues of Dimethachlon in three kinds of tobacco in Yunnan Province (Yunyan 85, Yunyan 87, K326), the test results showed that Dimethachlon digested rapidly in the tobacco leaves, the half-life was between 5.07 and 5.25 days. Dimethachlon were treated two times and interval seven days with the dosage of 2000 mL·hm-2 during the growing season of tobacco. The terminal residues level of Dimethachlon in three tobacco (Yunyan 85, Yunyan 87, K326)were all less than 0.180 mg·kg-1 after Dimethachlon being applicated for 25 days. Under the experimental conditions, theere were positive relationship between residues and amount as well as times, and negative relationship between residues and the days from last application to harvest.
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