| In China, chlormequat (CQ) and mepiquat (MQ) are two main plant growth regulators which have been widely applied to agricultural production. With the development of toxicology, studies have shown that even below the acceptable daily intake levels (ADI), CQ still has a negative effect on animal's reproductive capacity. CQ was categorized as one of the suspected endocrine disruptors, according to Registry of Toxic Effects of Chemical Substances (RTECS), a chemical toxicity database, released by National Institute for Occupational Safety and Health (NIOSH). Just between May 2000 and August 2002, seventeen rapid alert notifications involved the detection of unacceptable chlormequat residues in fresh fruits, vegetables and baby foods were delivered by European Commission. In 2006, ketchups from twenty four factories in Xinjiang province were found with CQ and MQ residues far beyond EU standard and therefore were forbidden to export to EU, United States and Japan. In consequences, researchers are paying more attention towards CQ and MQ residues in agricultural products. But little research on CQ and MQ has done in China. The standard method for detecting CQ and MQ in tomatoes had not yet been established. Therefore, to develop a method to study CQ and MQ residues in tomatoes has a very practical significance.First, this study established the LC-MS/MS method to determinate CQ and MQ residues in tomatoes and tomato juice matrix. The instrument parameters, flow ratio, mobile phase, and pre-processing method have been optimized. The results showed that: the recovery of CQ and MQ in tomato matrix was between 86.9% and 104.49%, and the relative standard deviation was from 0.59% to 7.4%. In tomato juice matrix, CQ and MQ had the recovery between 98.66% and 116.95%, and the relative standard deviation was from 0.29% to 1.72%. The instrument detection limit for CQ and MQ were 0.05μg/kg, 0.07μg/kg, separately. The method detection limit was 0.005 mg/kg. These can fully meet the requirements of the international residue limits. At the same time, this method can be applied to rape, cucumber, grape and other different matrices. For quaternary ammonium diquat (DQ) and difenzoquat (DF), this method was also suitable.Based on the optimized method, 50 cheery tomato samples from Beijing markets were randomly selected in order to detect the residues of CQ and MQ in this study. The results reveled that: 34 samples out of 50 were found to have CQ residue from 0.01 mg/kg to 9.44 mg/kg, which made the detection rate 68%, 46% exceeded the maximum residue limit according to EU standard. 5 samples contained MQ residue from 0.01 mg/kg to 0.37 mg/kg, which made the detection rate 10%, 6% over the Japanese standard. In accordance with JMPR acute dietary risk assessment, this study estimated that CQ and MQ in tomato had the risk of 14% and 0.1%, separately. At the same time, our study also compared different cleaning methods on their residual effects. For CQ and MQ residues, washing with water or soaking for 30 minutes had no significant effect.This paper also focused on the preliminary residue of CQ and MQ in cherry tomato. In a field test carried out in Shandong province, the results showed that: CQ and MQ in soil can be easily degradated. The half life period of CQ and MQ are 12.4 day and 1 day, respectively. But the degradation of CQ and MQ in the fruits was not that significant. In Langfang plant simulation, we found the same pattern through experiment in 56 days. Although our research of CQ and MQ residues was in one place for one year, but it's recommended that industry and management should pay more attention to the experimental results.
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