| As the increasingly used of chiral pesticide in the agricultural production,chiral pesticide poses a serious problem to agricultural environment and biological safety.Chiral pesticide enantiomers have the same physical and chemical properties and used as mixtures,butchiral enantiomers often show significant stereoselectivity in chiral environment.The separation of chiral compounds and corresponding simultaneous determination method are the basis of the study on the stereoselective environmental behavior,activity,toxicity and correlative ecological risk of enantiomers.Therefore,it is helpful to solve the problem by carrying out the enantiomers separation analysis and metabolic study of chiral pesticides based on liquid chromatography-tandem mass spectrometry for its high selectivity,high sensitivity,and simple preliminary treatment.In this paper,the chromatographic separation and corresponding simultaneous determination methods of a variety of fungicides with asymmetric C,S and P atom as chiral center were established.Furthermore,the environmental behavior of triazole fungicides on fruits as well as vegetables and isocarbophos in soil was investigated.The main results were as follows:Firstly,mandipropamid enantiomers separation was investigated on five kinds of chiral analytical column using HPLC-MS/MS excellent separation effect was obtained on Lux Cellulose-2 column.The influence of mobile phase composition and column temperature enantiomers on the splitting was further investigated.Satisfactory separation was achieved within 4 minutes under the below conditions:Lux Cellulose-2 selected as the chiral column,the mobile phase being methanol(contains 0.1%formic acid):0.1%formic acid aqueous solution(85:15,v/v),the column temperature being 25?.Based on calculated circular dichroism(CD)spectrum and detected CD spectrum,the absolute configuration of mandipropamid enatiomers was identified.Based on the QuEchERS method,the detection method of the enantiomers in four kinds of fruit and vegetable samples(potatoes,peppers,grapes,watermelon)was established.The results showed that the method can meet the requirement of simultaneous determination of the mandipropamid enantiomers in fruits and vegetables by evaluating the accuracy and sensitivity.Secondly,separation of fenarimol and nuarimol enantiomers was investigated on Lux Cellulose-1,Lux Cellulose-2 and Lux Cellulose-3 using HPLC-MS/MS,and the results showed that Lux Cellulose-3 shown satisfied separation effect for both of fenarimol and nuarimol enantiomers.On the basis of the above results,the separation effect of the mobile phase composition and column temperature on the Lux Cellulose-3 was optimized.Finally,the optimal chromatographic separation conditions were under the below conditions:Lux Cellulose-3 chiral column,the mobile phase composed of methanol/0.1%formic acid(80:20,v/v),and the column temperature of 25?.Under this condition,the baseline separation of the two fungicides enantiomers can be achieved within 8 minutes.Based on calculated circular dichroism(CD)spectrum and detected CD spectrum,the absolute configuration of fenarimol and nuarimol enatiomers was identifi ed.Combined with QuEchERS method,simultaneous determination method of two fungicides in soil,fruit(apple,grape)and vegetable(cucumber and tomato)matrix was established.The results showed that this method could be used for the determination of the enantioselective degradation of fenarimol and nuarimol enantiomers in fruits,vegetables and environmental samples.Thirdly,three kinds of phenylamide fungicides(benalaxyl,furalaxyl and metalaxyl)enantiomers separation were investigated on five kinds of chiral column using HPLC-MS/MS.The results showed that baseline separation of three kinds of fungicides can be achieved at the same time on Lux Cellulose-4 chiral column.The best chromatographic separation conditions was confirmed as the mobile phase composed of acetonitrile/0.1%formic acid(45:55,v/v);the simultaneous determination of the three fungicides enantiomers in fruit(grape),vegetable(cucumber)were established using QuEChERS method.The results showed that this method can be used for the determination of the trace benalaxyl,furalaxyl and metalaxyl enantiomers in fruits and vegetables,and also used for the stereoselective degradation of enantiomers in other plant and environmental samples.Metalaxyl were determined in five grapes sample and two cucumber samples of sixty commercial samples,and the concentration ranged in 0.0068-0.23 mg kg-1.The significant differences in the enantiomers concentritons of metalaxyl showed that the stereoselective degradation may happen in cucumber and grape samples.Fourthly,the enantioseparation of twenty-one kinds of triazole chiral fungicides was investigated on four different chiral stationary phases(Lux Cellulose-1,Lux Cellulose-2,Lux Cellulose-3 and Lux Amylose-2)using HPLC-MS/MS.Better separation was obtained on Lux Cellulose-1 and Lux Cellulose-2 compared with on Lux Amylose-2 for triazole fungicides enantiomers.Lux Cellulose-2 was a good supplement to the Lux Cellulose-1 column.The twenty fungicides were completely separated on the Lux Cellulose-1 and Lux Cellulose-2 by optimizing the experimental conditions.The method of enantioseparation of triazole fungicides is beneficial to the determination of these pesticides at lower concentrations in food and environmental samples,and it is also used to study enantioselective degradation behavior of these triazole fungicides.Fifthly,the stereoselective environmental behavior of triazole fungicides(tebuconazole,tetraconazole,myclobutanil and fenbuconazole)in strawberries was studied.The results showed that the degradation of R-and S-enantiomer of each fungicide on strawberries was well described by single first-order kinetics equation.(+)-Tebuconazole was preferentially degraded in strawberry and the EF value 30th day after spraying reached 0.401.Myclobutanil was degraded preferentially in strawberry,and the EF value reached 0.371 after 21 days.There was no significant enantioselectivity observed in degradation processes of tetraconazole and fenbuconazole in strawberry.Sixthly,the enantiomers separation of the phenylpyrazole insecticide ethiprole was investigated on Lux Cellulose-1,Lux Cellulose-2 and Lux Cellulose-3 chiral columns by HPLC-MS/MS.Satisfied baseline separation of ethiprole enantiomers was obtained on Lux Cellulose-2.The optimum chromatographic separation conditions used Lux Cellulose-2 chiral column,at column temperature of 25? with methanol/water(60:40,v/v)as mobile phase at flow rate of 0.25 mL min-1.In this condition,the baseline separation of the two enantiomers can be achieved in 15 minutes.On this basis,the method of simultaneous determination ethiprole enantiomers in rice substrates was established.The results showed that at levels,the average recoveries of the ethiprole enantiomers was 87.4%-97.8%with RSD in the range of 3.1%-9.3%at the spikied level of 0.01-0.2 mg kg-1,the detection limit(LOD)was confirmed as 0.001 mg kg-1 and the quantitative limit(LOQ)was 0.003 mg kg"1.It can be used for stereoselective detection of ethiprole in rice samples.Seventhly,The enantioseparation of isocarbophoswere investigated on six kinds of chiral columns(Lux Cellulose-1,Lux Cellulose-2 and Lux Cellulose-3,Lux Cellulose-4,Lux amylose-2 and Chiralpak AD-3R)by HPLC-MS/MS.As a result,with Lux-cellulose-1,Lux Cellulose-2,Lux-cellulose-4,Chiralpak AD-3R and Lux-amylose-2,'the baseline separation of the enantiomers can be achieved.The mobile phase and column temperature were further discussed on Chiralpak AD-3R.With Chiralpak AD-3R and acetonitrile-water(60:40,v/v)being the mobile phase,the enantiomers can be separated in 3 minutes.It is appliable for fast detection of isocarbophos enantiomers.Furthermore,the simultaneous determination method of isocarbophos enantiomers in orange pulp,peel,and kumquat was established.Based on calculated circular dichroism(CD)spectrum and detected CD spectrum,the absolute configuration of isocarbophos enatiomers was identified.The results showed that the average recoveries of soil samples spikied at 0.05,0.5 and 5.0 ?g kg-1 were 89.2-97.1%,RSD value was 2.1-8.8%,and LOD was confirmed as 0.005 mg kg-1.The average.recoveries of orange pulp,peel,and kumquat sample in 5,50,250 ?g kg-1 concentration were 76.1-95.4%,RSD value was less than 11.1%and LOD was in the range of 0.0002-0.0005 mg kg-1.It could satisfy the stereoselective detection of trace amounts of isocarbophos residues in soil and kumquat samples.Finally,an enantioselective method is established for the determination of isocarbophos in soil by HPLC-MS/MS.The pesticide residues in soil samples were extracted with acetonitrile,and complete enantioseparation was obtained on an amylose tris(3,5-dimethyl phenylcarbamate)chiral column using acetonitrile/2 mM ammonium acetate solution containing 0.1%formic acid(60:40,v/v)as the mobile phase.The method was utilized to investigate the degradation of isocarbophos in soils(Changchun,Hangzhou,andZhengzhou)under sterilized or native conditions.There was no enantioselectivity for isocarbophos enantiomers in the sterilized condition.The degradation behavior of rac-isocarbophos was various under native conditions,with no enantioselectivity in the Changchun soil and with the S-(+)-isocarbophos enriched in the Hangzhou and Zhengzhou soils.In addition,more isocarbophos was degraded under alkaline conditions. |
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