The Analysis Methods And The Residue Dynamics Study Of Metribuzin And Its Major Metabolites Of Tomatoes

Methods of gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry were developed to determine the residues of herbicide of metribuzin and its metabolites deaminodiketometribuzin(DADK), deaminometribuzin(DA), diketometribuzin(DK) in soils, tomatoes and its plants. The residue dynamics of metribuzin and its metabolites in tomato field were studied. The main contents and results were as follows:The methods of gas chromatography-mass spectrometry (GC-MS):five organic solvents of ethyl acetate, ethanol, methanol, acetone, and acetonitrile were selected as extractant, respectively, and then followed by ultrasonic extraction, shaking apparatus extraction and pressurized liquid extraction. Finally, the samples were purified by primary secondary amine (PSA) and solid phase extraction (SPE) micro-column, and detected by GC-MS. A large number of recovery experiments showed that the optimal pretreatment conditions of detecting metribuzin, DA, DK and DADK in soil, tomato plants and tomato fruits were:using acetonitrile as extractant combined with ultrasonic extraction and purified by PSA reagent and graphite carbon SPE column. When added0.1,0.5,1mg/kg mixture pesticides of metribuzin, DA, DK and DADK to blank samples, the average recoveries were76.79-90.47%,75.48-91.62%,73.79-90.82%and78.17-93.08%in soils respectively; the determination limits were0.0013,0.001,0.0013and0.0055mg/kg; and the relative deviations were from1.96to6.27%. As to tomato plants samples, the average recoveries were75.30-87.85%,72.16-81.76%,73.33-79.13%and73.2-85.0%respectively; the determination limits were0.004,0.005,0.004and0.011mg/kg; and the relative deviations were from1.71to5.98%. In tomato samples, the average recoveries were77.02-83.86%,76.34-78.7%,73.45-79.23%and75.57-85.13%respectively; the determination limits were0.002,0.004,0.003and0.010mg/kg; and the relative deviations were from1.80to6.80%. All the indicators met the requirements of guideline on pesticide trials.The methods of liquid chromatography-mass spectrometry:Xbridge C18separation column (2.1×30mm,3.5μm) and acetonitrile-water (V:V=75:25) were used to separate the mixture, electrospray ionization (ESI) was chosen to determine metribuzin and its metabolites with positive and negative scanning simultaneously. When added0.1,0.5,1mg/kg mixture pesticides of metribuzin, DA, DK and DADK to blank samples, the average recoveries were80.8-89.2%,83-87.3%,70.3-71.0%and71.6-74.4%; the determination limits were0.0010,0.0005,0.0080and0.0380mg/kg; and the relative deviation were from2.1to5.3%in soils respectively. As to tomato plants samples, the average recoveries were76.0-81.0%,74.4-90.1%,70.2-78.0%and70.0-73.0%; the determination limits were0.004,0.002,0.012and0.046mg/kg; and the relative deviations were from1.8to7.0%respectively. In tomato samples, the average recoveries were78.3-82.5%,79.9-88.0%,74.0-79.3%and71.3-72.0%; the determination limits were0.003,0.002,0.010and0.037mg/kg; and the relative deviations were from1.9to7.7%respectively. All the indicators met the requirements of guideline on pesticide trials.The dynamic and final residues of metribuzin and its metabolites in soils, tomatoes and its plants the degradation procedure of metribuzin was correspond to the mathematic pattern,C=C0e-kt, both in soil and in tomato plants. The dynamic equation in soil was y=4.6e-0.6667x and its half-life was1.04day; in tomato plants, the dynamic equation was y=0.52e-0.5464x and its half-life was1.27day. The residues of metribuzin and its metabolites in maturity tomatoes were determined by LC-MS and GC-MS at the same time. Except for DADK, metribuzin, DA and DK were not detected out, and the residue of DADK was0.019mg/kg in the low-dose pesticide area; in high-dose pesticide area, metribuzin and DA were not detected out, while DK, DADK contents were0.002,0.149mg/kg respectively.The methods were systematically studied that metribuzin and its major metabolite could be determined simultaneously. They were sensitive, simple and repeatable, which could be applied in the determination of large number of soil, fruits and vegetables.