Study On The Simultaneous Detection Method For Multi-residue Of Agricultural Chemicals In Orchard Soil

The excessive and unreasonable use of agricultural chemicals brought about serious harm to the environment, reduced the quality of agricultural products, and led to the potential harm to human health. Food safety problem caused by the agricultural chemicals residues has occurred from time to time. After our country joined WTO, the developed country increased the detection range of agricultural chemicals residues of imports agricultural products and reduced the maximal residue limits of agricultural chemicals by its technical advantages. This caused a large amount of agricultural products of China exceeded the limit standards of agricultural chemicals, and were rejected or returned, and thus brought serious challenge to agricultural products trade. In order to protect human health and normal export trade of our country, it is a pressing matter to control pesticide residues. The foundation is to establish sensitive and reliable detection method for multi-residues of agricultural chemicals.After the investigation of the agricultural chemicals commonly used in orchard soil in Gold Orchard of Chongqing, some agricultural chemicals including herbicides (paraquat and glyphosate), insecticides and their metabolites (dimethoate, omethoate, bifenthrin, and cyhalothrin), and fungicide its metabolite (thiophanate methyl and carbendazol) were selected as research objects in this study. Based on the properties of agricultural chemicals, the conditions of sample extraction and purification were optimized, and established simultaneous detection methods by using high performance liquid chromatography (HPLC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the main results obtained were summarized as follows:1. A simultaneous determination method for the residues of paraquat and glyphosate in orchard soil was developed. Optimize the extraction conditions of soil samples, with potassium dihydrogen phosphate buffer (pH=6.5) as extracting agent with ultrasonic extraction. The working conditions of chromatographic instrumentation for paraquat and glyphosate were obtained, i.e., acetonitrile-potassium dihydrogen ph(?)phate (heptane sulfonate, pH=2.5) was used as the mobile phases with UV detection at265nm. Two herbicides were separated within13min with good linear ranges. The average spiked recoveries of paraquat and glyphosate ranged from74.86%to95.73%with the relative standard deviations (RSDs) of1.57%～5.67%, and the limits of detection were93and60μg/kg, respectively.2. Simultaneous determination methods for the residues of insecticide, fungicide and their metabolites in orchard soil were developed. The working conditions of HPLC and LC-MS/MS instrumentation for omethoate, dimethoate, carbendazol, thiophanate methyl, cyhalothrin and bifenthrin were obtained. Soil samples were extracted by dichloromethane-methanol (V/V=1/1), cleaned up by LC-AI-N solid phase extraction (SPE) column. For HPLC analysis, the average spiked recoveries of omethoate, dimethoate, carbendazol, thiophanate methyl, cyhalothrin and bifenthrin ranged from71.77%to120.89%with RSDs of4.19%-9.54%, and the limits of detection were90,80,64,38,0.032and34μg/kg, respectively. For LC-MS/MS analysis, the average spiked recoveries of the above6compounds ranged from72.02%to110.56%with RSDs of2.66%-7.99%, and the limits of detection were0.5,0.2,0.2,0.5,1and1μg/kg, respectively.3. The proposed HPLC and LC-MS/MS methods were successfully applied to detect the actual soil samples collected from Gold Orchard of Chongqing. The results showed that trace bifenthrin was detected in pear orchard soil with the amount of2.5g/kg.