| Hydrolysis and the photodegradation are the most important degradation pathways of pesticide, and have a decisive role for residence time of pesticide in the environment. This study choosed bifenazate as the research object, used HPLC to study its hydrolysis and photodegradation behaviors in different environments, and analyzed its degradation products after hydrolysis and photodegradation by LC-MS, then speculated its possible hydrolysis and photodegradation pathways. These results have important environmental ecology significance for guiding the scientific and reasonable use of bifenazate, and reduce its pollution to the environment, and its risk assessment. Main results are as follows :(1) Designed 9 new HPLC detection methods of bifenazate, and Agilent Eclipse Plus C18 as the chromatographic column (250 mm×4.6 mm,5 μm), DAD as the detectionacetonitrile:water= 70 : 30 as the mobile phase,0.8ml/min as the flow rate, injection volume,10μL, determine wavelength,230nm, showed the lowest LOD(0.01 mg·L-1) and shortest peak time, and target peak completely separated with artifactual bands, and had a good shape;(2) Established a new LC-MS detection menthod of bifenazate:ESI for the ion source; positive ion mode scanning; scanned area : 50 Da — 500 Da; IS : 5500 V; CUR:30.0 Psi; GS1:30.0 Psi; GS2:60.0 Psi; TEM:550℃; CAD:High; DP:25 V; EP:10 V; dwell time:0.3 second(3) Kind and volume of extraction and disperser solvent, extraction time, and salt effect in VALLME procedure were studied which could affect the extract efficiency, results showed 0.3mL dichloroethane as extractant, 1mL acetone as disperser solvent, extraction for lmin with vortex assistance, no salt in the sample solution, centrifugation at 4500 rpm for 5min showed the best extract efficiency (than 89% for recovery) and good repeatabilities were obtained with relative standard deviation (% RSD) less than 5.7%;(4) The hydrolysis speed of bifenazate became slower with the initial concentration increased; with temperature increased, the speed of hydrolysis reaction became faster, the activation energy and temperature had negative correlation and the absolute values of activation entropy had positive correlation with temperature; the speed became faster with the value of pH increased, belonging to basic hydrolysis, its degradation mechanism maybe related to its ester bond in its chemical construction; the speeds of bifenazate in river water, lake water, tap water and sterile river water were positive correlation with the pH of waters, all hydrolysis reactions of bifenazate fitted to first order pharmacokinetic model;(5) The speeds of photodegradation of bifenazate in different illuminants were 300W high pressure mercury lamp was faster than 15W UV lamp,300W xenon lamp slowest, and from fast to slow was ethyl acetate, acetonitrile, methanol, acetone; acetonitrile had no photosensitivity and optical quenching, so we could infer that ethyl acetate had photosensitization on bifenazate photodegradation, while methanol and acetone had photoquenching effect on bifenazate photodegradation;(6) In 15 W UV lamp, with the value of pH increased, the speed of photodegradation of bifenazate was faster; in different natural waters, the speed of photodegradation from fast to slow was sterile river water, sterile lake water, tap water, river water, lake water, pure water, and had positive correlation with the pH of waters;(7) Via LC-MS, traced analysis the hydrolysis product of bifenazate, and we got the graphs of the TIC and MS of hydrolysis products of bifenazate; and via qualitative analysis, we speculated three kinds of hydrolysis product of bifenazate, i.e. C17H18N2O3, C14H12N2O and C13H12O; according to the hydrolysis products and the way of chemical bond rupture, we preliminary presumpted that the hydrolysis way was: bifenazate turned into bifenazate diazene under the action of water molecular, then ester bond of diazene was attacked by OH", and came up basic hydrolysis with bond rupture, producd carboxylic acid, carboxylic acid moved forward with hydrolysis, formed smaller molecular weight and simpler structure,4-methoxy-biphenyl;(8) Via LC-MS, traced analysis the photolytic products of bifenazate, and we got the graphs of the TIC and MS of photolytic products of bifenazate; and via qualitative analysis, we speculated five kinds of photolytic product of bifenazate, i.e. C17H18N2O3, C14H12N2O3, C12H10, C13H13NO, C13H12N2O and two kinds of unknown structure products (The relative molecular masses of the ionization ion were 217.6/239.3 and 242.2); according to the photolytic products and the way of chemical bond rupture, we preliminary presumpted that the photolytic way was : bifenazate under the action of UV lamp, turned into bifenazate diazene, then ester bond of diazene was attacked by OH, and came up basic hydrolysis with bond rupture, producd carboxylic acid, carboxylic acid moved forward under the action of photon, formed 4-methoxy-biphenyl-3-yl-diazene, then gradually formed 4-Methoxy-biphenyl-3-ylamine, biphenyl. |
