| Welsh onion, a traditional condiment vegetable, which is one of China’s the most important export vegetables. The risk of pathogens, pests and weeds epidemic when crops are grown under such intensive regimes and the increase of the multiple crop indexes. The use of chemical pesticides is still one of the most important instruments for pest control. However, in recent years, welsh onion for export often encounters with the foreign technical barriers because that pesticides residues exceed maximum residue limit. Choosing the low-risk pesticides and developing rapid detection of pesticide residues are both the key of preventing pesticides residues exceed maximum residue limit. They are also the basic of controlling pesticides residues, ensuring food safety and avoiding trade dispute between countries.This research, optimized the steps before samples extract and purification, developed a simple, rapid and high sensitiveness analysis method of gas chromatography-mass spectrometric (GC/MS) in welsh onion. Established an analysis method of liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) in welsh onion depending on some new kinds of pesticides that were widely used, thermally unstable and highly polar in recent years. Meantime, the characters of multi-pesticides residues in spring welsh onion were also determined. The results of this research would be the theoretical basis of rationally use of pesticides in welsh onion and better deal with the foreign technical barriers. The results are as follows:1. A GC/MS method was developed by optimizing the procedure of extraction and purification for the determination of193pesticide residues in welsh onion. The analytes were extracted from the samples using1%acetic acid acetonitrile. The extracts were cleaned up by SPE column filled with C18/PSA, eluted using acetonitrile, and followed by determination with GC-MS at selected ion monitor mode (SIM) using TPP as internal standard. All of the tested pesticides showed good linear relationship (r≥0.9967) between10μg/L to1000μg/L The limits of detection (LOD) and limits of quantification (LOQ) of the method were0.04μg/kg-8.11μg/kg,0.13μg/kg-27.03μg/kg. The mean recoveries for welsh onion, spinach, strawberry and apple samples at three spiked concentrations levels of10,20,50μg/kg were73.3%-108.8%, with relative standard deviations (RSD, n=6) was2.8%-11.9%. The method was simple, sensitive and accurate, and could be used for the routine analysis of193pesticide residues in welsh onion.2. A method was established to determine36pesticides that were thermal unstable or/and high polar residues in welsh onion. The analytes were extracted from the samples using1%acetic acid acetonitrile, and purified by dispersion solid phase extration using C18and PSA as solidphase, then analyzed by HPLC/MS/MS with multiple-reaction monitoring (MRM), quantified using an external standard. The interference of matrix was reduced by the matrix-matched calibration standards curve. A good linear of the calibration curve developed were exhibited over a concentration range of1μg/L to100μg/L for the36pesticides with a correlation coefficient of0.99960to0.9999.The limits of quantification were0.22μg/kg to9.80μg/kg and the limits of detection were0.07μg/kg to2.94μg/kg. The mean recoveries for welsh onion, spinach, strawberry and apple samples at three spiked concentrations levels of5,10,20μg/kg were82.3%-107.4%with relative standard deviations (RSD, n=6) of2.0%-10.0%.3. A method was established to determination of cyromazine residuse in welsh onion. The samples were extracted with acetonitrile and purified by dispersion solid phase extraction using PSA as solid phase. Then analyzed by HPLC-MS/MS with mulpitle-reaction monitoring (MRM) under positive ion mode of electrospray ionization (ESI), quantified by the external standard. The results showed that the good linearity was achieved in the range of2-200μg/L for cyromazine, the linear correlation coefficient was0.9995. The fortified recovery at level of10,20,50μg/kg ranged from80.6%to87.2%, with relative standar deviation of2.8%～6.1%. The limit of detection for cyromazine in welsh onion was0.58μg/kg and the limit of quantification was1.94μg/kg。4. The field residue dynamics study and final residue trials of pyrimethanil and diethofencarb in spring welsh onion growing of gray mold in Shandong province, China were designed. The field residue dynamics study showed that the half-lives of pyrimethanil and diethofencarb in welsh onion was4.1d and3.1d, respectively. It is shown that pyrimethanil and diethofencarb belonged to non-persistent pesticides (Ti/2<30d). When the welsh onion was sprayed of26%pyrimthanil-diethofencarb WP for2～3successive times at application dose (pyrimthanil180g ai/hm2, diethofencarb288g ai/hm2) and at double dose(pyrimthanil360g ai/hm, diethofencarb576g ai/hm), at7,14and21th day after the last application, the final residues of pyrimethanil and diethofencarb in welsh onion were between0.007～0.560mg/kg and ND～0.394mg/kg, respectively, which were below the MRLs of Japan, the United States of America (USA) and European Union (EU), which are the major importing country of welsh onion.5. The field residue dynamics study and final residue trials of dimethomorph in spring welsh onion growing of blight and/or downy mildew in Shandong province, China were designed. The field residue dynamics study showed that the half-lives of dimethomorph in welsh onion was3.5d. It’s shown that dimethomorph belonged to non-persistent pesticides (T1/2<30d). When the welsh onion was sprayed of50%dimethomorph WP for2-3successive times at application dose (360g ai/hm2) and at double dose(720g a i/hm2), at7th,14th and21th day after the last application, the final residues of dimethomorph in welsh onion were between0.0094-0.681mg/kg, which were below the MRLs of Japan, the United States of America (USA) and European Union (EU), which are the major importing country of welsh onion.6. The field residue dynamics study and final residue trials of myclobutanil in spring welsh onion growing of rust disease and/or brown patch in Shandong province, China were designed. The field residue dynamics study showed that the half-lives of myclobutanil in welsh onion was3.4d. It’s shown that myclobutanil belonged to non-persistent pesticides (T1/2<30d). When the welsh onion was sprayed of12.5%myclobutanil EC for2-3successive times at application dose (62.5mg a.i./kg) and at double dose (125.0mg a.i./kg), at7th and14th day after the last application, the final residues of myclobutanil in welsh onion were between0.003-0.017mg/kg, which were below the MRLs of Japan, the United states of America (USA) and European Union (EU), which are the major importing country of welsh onion.7. The field residue dynamics study and final residue trials of phendimethalin in spring welsh onion when transplanting in Shandong province, China were designed. The field residue dynamics study showed that the half-lives of phendimethalin in welsh onion was3.8d. It’s shown that phendimethalin belonged to non-persistent pesticides (T1/2<30d). When the soil of planting welsh onion was handled by33%phendimethalin EC at application dose (742.5g ai/hm2) and at double dose (1485g ai/hm2), at80th day after application, namely time for harvesting the final residues of phendimethalin in welsh onion were below the limit of detection for phendimethalin in welsh onion (0.88μg/kg), which were below the MRLs of Japan, the United States of America (USA) and European Union (EU), which are the major importing country of welsh onion.8. The field residue dynamics study and final residue trials of cyromazine in spring welsh onion when transplanting in Shandong province, China were designed. The field residue dynamics study showed that the half-lives of cyromazine in welsh onion was8.8d. It’s shown that cyromazine belonged to non-persistent pesticides (T1/2<30d). When the root of welsh onion was poured by50%cyromazine WP at application dose (450g ai/hm2) and at double dose(900g ai/hm2), at80th day after application, namely time for harvesting the final residues of cyromazine in welsh onion were below the limit of detection for cyromazine in welsh onion (0.88μg/kg), which were below the MRLs of Japan, the United States of America (USA) and European Union (EU), which are the major importing country of welsh onion. |
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