| The enantiomeric separation of five triazole fungicides was analyzed by high-performance liquid chromatography (HPLC) on the new coated type amylose-tris (5-chlorine-dimethy-phenylcarbamate) chiral stationary phase under reverses phase. Firstly, the effects of different mobile phase composition (acetonitrile/water) and temperature of column (5-45℃) in the chiral separation were investigated. Secondly, elution order of triadimenol, triadimefon, diniconazole and tebuconazole was measured by high performance liquid chromatography which coupled with CHIRALYSER-MP polarimetric detector. Thirdly, the analytical methods for enantiomers of tebuconazole in cabbage (plant), cucumber (fruit) and soil matrix were established. At last, stereoselective degradation of tebuconazole enantiomers in cabbage, cucumber and soil was investigated based on the analytical method. It was the first report about chiral separation of triazole pesticides as well as the study of stereoselective degradation of tebuconazole enantiomers in cabbage, cucumber and soil using amylose-tris (5-chlorine-dimethy-phenylcarbamate) chiral stationary phase. Results illustrated as follows:(1) The optimized separation of triadimenol enantiomers was 25℃with acetonitrile/water 30/70 (V/V), moreover, thermodynamical parameters illustrated that enantiomeric separation of triadimenol were driven by enthalpy. Triadimefon enantiomers were separated under the optimized proportion of acetonitrile/water 35/65 (V/V) as well as the temperature was 35℃, furthermore, thermodynamical parameters indicated that enantiomeric separation of triadimefon were driven by entropy. Baseline separation of diniconazole were not obtained within observed mobile phase (acetonitrile content ranged from 100% to 30%) and temperature (5-45℃), better separation achieved with acetonitrile/water 40/60 (V/V) and 25℃. Additionally, thermodynamical parameters illustrated that enantiomeric separation of diniconazole was driven by enthalpy. In terms of tebuconazole, baseline separation of enantiomers achieved with every proportion of acetonitrile/water, while the content of acetonitrile ranged from 100% to 40%, and thermodynamical parameters indicated that enantiomeric separation of tebuconazole were driven by enthalpy. No separation tendency was obtained on that chiral solid phase for hexaconazole enantiomers. Those factors which influenced the chiral separation mechanism were contributed by the structure of chiral solid phase, the composition of mobile phase, temperature as well as the configuration of solute which was considered to be the key character in chiral recognition when hexaconazole was not separated at the same conditions comparing with other four fungicides.(2) Based on former research, absolute configuration of fungicides was confirmed. Results illustrated that all (-)-R-enantiomers of triadimefon (acetonitrile/water 35/65, V/V), diniconazole (acetonitrile/water 40/60, V/V) and tebuconazole (acetonitrile/water 50/50, V/V) were eluted before the (+)-S-enantiomers.(3) Good linear calibration curves were obtained (R2>0.9997); average recoveries of tebuconazole ranged from 82.02±1.01% to 100.23±1.18% in cabbage, and from 85.03±0.20% to 91.73±4.20% in soil at the racemic fortified levels of 0.1~10.0mg/kg; average recoveries of tebuconazole in cucumber ranged from 91.21±2.95% to 101.11±5.73 % at the racemic fortified levels of 0.01~1.0mg/kg; the relative standard deviation (RSD) of the method was under 15.0%; The limit of detection (LOD) for both enantiomers was 0.01μg/g of soil and cabbage samples, and the limit of quantification (LOQ) was 0.025μg/g; The LOD and LOQ of method in cucumber were 0.001μg/g and 0.003μg/g respectively.(4) Degradation kinetics of tebuconazole in the test cabbage, cucumber and soil followed first-order kinetics; the stereoselective degradation of enantiomers was found in cabbage and cucumber, and the degrade pace of enantiomers was difference in the two matrixes; there was a preferential degradation of (+)-S-tebuconazole (T1/2=7.81) in cabbage, which faster than (-)-R-tebuconazole (T1/2=10.50), ES=-0.146, and EF peaked at 0.707±0.025 in the 28th day after foliar treatment. By comparison, preferential degradation of (-)-R-tebuconazole (T1/2 = 0.93) occurred in cucumber, which faster than (+)-S-tebuconazole (T1/2=1.68), ES=0.289, and EF reached to 0.310±0.19 in the 10th day after treatment; there was no obvious stereoselective degradation of tebuconazole enantiomers in tested soil, which the degrade pace of (+)-S-tebuconazole (T1/2=11.27) was almost the same as (-)-R-tebuconazole (T1/2=11.20), ES=0.003. |
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