Quantitative Analysis Of Myclobutanil And Indoxacarb Enantiomers Residue In Vegetable And Fruit

Chiral pesticides are mostly commercialized as racemates, that is, mixtures of enantiomers, which may selectively interact with biological systems and nantioselective toxicity, and possibly bring harm to man and environment. But the research on chiral pesticides enantiomers is in its infancy, studies about the degradation and toxicology of enantioselectivities is relatively less. It is of great significance to develop enantiomeric analysis methods of chiral pesticides for the individual enantiomer to supply more accurate method for evaluating the foods and environmental risk. The methods have been developed for the determination of myclobutanil and indoxacarb enantiomers residue in vegetable and fruit. And UPLC-MS/MS used in the analysis of chiral pesticides has strong support ability for the fate of enantiomers. The dissertation consisted of four chapters.It briefly outlined the basic concept of chiral pesticides and research status situation of theirs environment behavior, elaborated with emphasis on the current progress of enantioselectivities. Finally, it proposed the objectives and significance of the research.The enantiomer of myclobutanil was resolved under reverse phase ultra liquid chromatography-mass spectrometry (UPLC-MS/MS) using Chiralcel OD-RH with acetonitrile-water as a mobile phase. The effects of the content of acetonitrile in mobile phase, flow-rate and temperature on the chiral separation of myclobutanil were studied, and the enantiomers were identified by a chiral detector. The results showed that good enantiomeric separations were achieved with both CSPs under experiment of flow-rate 0.5mL/min, acetonitrile-water 60:40 in volume and temperature is 25 oC. The first enantiomer is (+)-myclobutanil and the next one is (-)-myclobutanil.A method was developed for determining myclobutanil enantiomers residue in cucumber and soil by ultra liquid chromatography-mass spectrometry. Myclobutanil was extracted with acetonitrile and cleaned up with SPE, detected by ultra liquid chromatography-mass spectrometry under multiple reaction monitoring mode. Average recoveries of myclobutanil in cucumber samples were found in the range of 77.6 %～100.7 % at spiking levels from 0.01 mg/kg to 0.2 mg/kg with relative standard deviations of 4.6 %～15.1 %. Limit of detections of myclobutanil enantiomers were 1.95~2.01μg/kg , while limit of quantifications were 6.50~6.71μg/kg.Average recoveries of myclobutanil enantiomer in soil samples were found in the range of 91.5 %~116.9 % at three spiking levels from 0.01 mg/kg to 0.2 mg/kg with relative standard deviations of 1.9 %~5.1 %. Limit of detections of myclobutanil enantiomer were 1.95~2.57μg/kg,while limit of quantifications were 6.50~8.58μg/kg,respectively.Enantiomeric separation of indoxacarb was performed by high performance liquid chromatography with the coating-typeamylose-tris [(S)–α-methyphenylcarbamate] used as the chiral stationary phase (CSP). The chromatographic conditions were optimized by studying the influences of the mobile phase composition including the concentration and type of the alcohol modifiers in hexane on enantiomers separation. The data indicated that the resolution of indoxacarb enantiomers decreased with the modifier contents in hexane increased. Correspondingly, as alcohol modifier, ethanol had a better modifier effect than isopropanol. The effect of temperature on chiral separation was investigated and it showed that a higher column temperature resulted in a higher separation efficiency for indoxacarb in the temperature range of 15～35 oC.An effective chiral analytical method was developed for resolving the enantiomers and quantitative determination of indoxacarb in vegetable and fruit. Indoxacarb was extracted with acetonitrile and cleaned up with SPE, detected by HPLC-AS column. The average recoveries in all matrixes of the pesticide ranged from 87.0 % to 116.9 % at 0.05, 0.1 and 5 mg/kg. The precision associated with the analytical method, expressed as RSDr, were <10.1% for the pesticide in all matrixes. LOD was 0.025 ~0.035 mg/kg and LOQ was 0.05 mg/kg for each enantiomer of indoxacarb in different matrixes.