Yuanbo Li

Chiral Triazole Fungicide Difenoconazole: Absolute Stereochemistry, Stereoselective Bioactivity, Aquatic Toxicity, and Environmental Behavior in Vegetables and Soil

In this study, the systemic assessments of the stereoisomers of triazole fungicide difenoconazole are reported for the first time, including absolute stereochemistry, stereoselective bioactivity toward pathogens (Alternaria sonali, Fulvia fulva, Botrytis cinerea, and Rhizoctonia solani), and toxicity toward aquatic organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Moreover, the stereoselective degradation of difenoconazole in vegetables (cucumber, Cucumis sativus and tomato, Lycopersicon esculentum) under field conditions and in soil under laboratory-controlled conditions (aerobic and anaerobic) was investigated. There were 1.33-24.2-fold and 1.04-6.78-fold differences in bioactivity and toxicity, respectively. Investigations on the stereoselective degradation of difenoconazole in vegetables showed that the highest-toxic and lowest-bioactive (2S,4S)-stereoisomer displays a different enrichment behavior in different plant species. Under aerobic or anaerobic conditions, (2R,4R)- and (2R,4S)-difenoconazole were preferentially degraded in the soil. Moreover, difenoconazole was configurationally stable in the test soil matrices. On the basis of biological activity, ecotoxicity, and environmental behavior, it is likely that the use of pure (2R,4S)-difenoconazole instead of the commercial stereoisomer mix may help to increase the bioactivity and reduce environmental pollution.

Simultaneous determination of cyflumetofen and its main metabolite residues in samples of plant and animal origin using multi-walled carbon nanotubes in dispersive solid-phase extraction and ultrahigh performance liquid chromatography–tandem mass spectrometry

A rapid and effective method for the simultaneous determination of cyflumetofen and its main metabolite residues in samples of plant and animal origin (tomato, apple, eggplant, soybean, green tea, fish, and pork liver) was developed using ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Samples were extracted with acetonitrile and cleaned-up with multi-walled carbon nanotubes (MWCNTs). The determination of the presence of target compounds was achieved in less than 4.0min using an electrospray ionization source in the positive mode (ESI+) for cyflumetofen and 2-(trifluoromethyl) benzamide (B-3) and the negative mode (ESI-) for α,α,α-trifluoro-o-toluic acid (B-1). The entire method was validated by evaluating the repeatability, linearity, precision, trueness, and matrix effect. Average recoveries of the analytes were in the range of 79.3-117.6% with relative standard deviation values below 7.6%. Limits of quantification (LOQs) ranged from 0.7 to 9.8μgkg(-1), which were lower than the maximum residue limits (MRLs) for the cyflumetofen found in foods in Japan.

Simultaneous enantioselective determination of triazole fungicides in soil and water by chiral liquid chromatography/tandem mass spectrometry.

The manuscript concerns the development and validation of a novel and sensitive multi-residue method for simultaneous enantiomeric analysis of 8 triazole fungicides (tetraconazole, fenbuconazole, epoxiconazole, diniconazole, hexaconazole, triadimefon, paclobutrazol, and myclobutanil) in soil and water using chiral liquid chromatography coupled with tandem mass spectrometry. The separation and determination were performed using reversed-phase chromatography on a cellulose chiral stationary phase, a Chiralcel OD-RH (150 mm × 4.6 mm) column, under isocratic conditions using a mixture of ACN-2 mM ammonium acetate in water (55/45, v/v) as the mobile phase at 0.45 mL/min flow rate. The effects of three cellulose-based columns and three amylose-based columns on the separation were also investigated. The QuEChERS (acronym for quick, easy, cheap, effective, rugged and safe) method and solid-phase extraction (SPE) were used for the extraction and clean-up of the soil and water samples, respectively. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. Under optimal conditions, the mean recoveries for all sixteen enantiomers from the soil samples were 76.4-108.1% with 2.6-12.0% intra-day relative standard deviations (RSD) and 4.2-14.1% inter-day RSD at 5, 25 and 50 μg/kg levels; the mean enantiomer recoveries from the water samples were 81.2-106.5% with 2.1-11.5% intra-day RSD and 3.4-13.6% inter-day RSD at 0.25, 0.5 and 2.5 μg/L levels. Coefficients of determination R2 ≥ 0.9989 were achieved for all studied analytes in the soil and water matrix calibration curves within the range of 1.0-125 μg/L. The limits of detection (LOD) (S/N=3) for all enantiomers in the soil and water were less than 1.0 μg/kg or μg/L, whereas the limit of quantification (LOQ) (S/N=10) did not exceed 3.0 μg/kg or μg/L. The results of the method validation confirm that this proposed method is convenient and reliable for the enantioselective determination of the enantiomers of triazole fungicides in soil and water.

Simultaneous determination of five pyrazole fungicides in cereals, vegetables and fruits using liquid chromatography/tandem mass spectrometry

The sensitive analytical method using quick, easy, cheap, effective, rugged, and safe (QuEChERS) procedure for simultaneous determination of five novel pyrazole fungicides residues in cereals (rice and wheat), vegetables (cucumber, tomato, and lettuce), and fruits (apple and grape) was developed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The five pyrazole fungicides (bixafen, fluxapyroxad, furametpyr, pyraclostrobin, and rabenzazole) were extracted from seven matrices using acetonitrile and subsequently cleaned up by octadecylsilane (C(18)) or graphitized carbon black (GCB) prior to LC-MS/MS analysis. The determination of the target compounds was achieved in less than 3.0min using an electrospray ionization source in positive mode (ESI+) for furametpyr, pyraclostrobin, and rabenzazole, while negative mode (ESI-) for bixafen and fluxapyroxad. The method showed excellent linearity (at least R(2)≥ 0.990) for all studied analytes. The limits of detection were below 3.0 μg kg(-1), and the limits of quantification did not exceed 9 μg kg(-1) in all matrices. The overall average recoveries in rice, wheat, cucumber, tomato, lettuce, apple, and grape at three levels (10, 100 and 1,000 μg kg(-1)) were ranged from 70.0% to 108% with all RSDs values less than 20.9% for all analytes. The method is demonstrated to be convenient and reliable for the routine monitoring of pyrazole fungicides in cereals, vegetables and fruits.

Enantioselective analysis of triazole fungicide myclobutanil in cucumber and soil under different application modes by chiral liquid chromatography/tandem mass spectrometry.

A sensitive and enantioselective method was developed and validated for the determination of myclobutanil enantiomers by chiral liquid chromatography coupled with tandem mass spectrometry. The separation and determination were performed using reversed-phase chromatography on a Chiralcel OD-RH column, with ACN-water (70/30, v/v) as the mobile phase under isocratic conditions at 0.5 mL/min flow rate. The matrix effect, linearity, precision, accuracy, and stability were evaluated. The proposed method then was successfully applied to the study of enantioselective degradation of rac-myclobutanil in cucumber and soil under different application modes. The results showed that the preferential degradation of (+)-myclobutanil resulted in an enrichment of the (-)-myclobutanil residue in plant and soil. Moreover, in cucumber, the stereoselective intensity of myclobutanil under root douche treatment was stronger than that under foliar spraying treatment, whereas in soil, the intensity was exactly opposite. The probable reasons underlying these enantioselective effects were also discussed. This study highlighted the importance of examining the fate of both enantiomers in the greenhouse system for the correct use of chiral pesticides.

Enantioselective determination of triazole fungicide simeconazole in vegetables, fruits, and cereals using modified QuEChERS (quick, easy, cheap, effective, rugged and safe) coupled to gas chromatography/tandem mass spectrometry

A rapid and effective method for enantioselective determination of simeconazole enantiomers in food products (cucumber, tomato, apple, pear, wheat and rice) has been developed. The enantiomers were resolved by capillary gas chromatography (GC) using a commercial chiral column (BGB-172) and a temperature program from 150°C (held for 1 min) and then raised at 10°C min(-1) to 240°C (held for 10 min). This enantioselective gas chromatographic separation was combined with a clean-up/enrichment procedure based on the modification of QuEChERS (quick, easy, cheap, effective, rugged and safe) method. Co-extractives were removed with graphitized carbon black/primary secondary amine (GCB/PSA) solid-phase extraction (SPE) cartridges using acetonitrile:toluene (3:1, v/v) as eluent. Gas chromatography/ion trap mass spectrometry (GC-ITMS) with electron ionization (EI) was then used for qualitative and quantitative determination of the simeconazole enantiomers. Two precursor-to-product ion transitions (m/z 121-101 and 195-153) with the best signal intensity were chosen to build the multiple-reaction monitoring (MRM) acquisition method. The limits of detection for each enantiomer of simeconazole in six food products ranged between 0.4 and 0.9 μg kg(-1), which were much lower than maximum residue levels (MRLs) established by Japan. The methodology was successfully applied for the enantioselective analysis of simeconazole enantiomers in real samples, indicating its efficacy in investigating the environmental stereochemistry of simeconazole in food matrix.

Simultaneous enantioselective determination of fenbuconazole and its main metabolites in soil and water by chiral liquid chromatography/tandem mass spectrometry

A novel and sensitive method was developed for the simultaneous determination of fenbuconazole and its main metabolites enantioselectively using chiral liquid chromatography coupled with tandem mass spectrometry. The separation and determination were performed using reversed-phase chromatography on a cellulose chiral stationary phase, a Chiralcel OD-RH (150 mm×4.6 mm) column, under isocratic conditions at 0.5 mL/min flow rate. The effects of three cellulose-based columns and three amylose-based columns on the separation were also investigated. The elution orders of the eluting enantiomers were identified by an optical rotation detector. The QuEChERS (acronym for Quick, Easy, Cheap, Effective, Rugged and Safe) method and solid-phase extraction (SPE) were used for the extraction and clean-up of the soil and water samples, respectively. Parameters including the matrix effect, linearity, precision, accuracy and stability were evaluated. Under optimal conditions, the mean recoveries for all enantiomers from the soil samples were 82.5-104.1% with 2.7-9.5% intra-day relative standard deviations (RSD) and 5.7-11.2% inter-day RSD at 5, 25 and 50 μg/kg levels; the mean enantiomer recoveries from the water samples were 81.8-104.6% with 2.6-11.4% intra-day RSD and 5.3-10.4% inter-day RSD at 0.25, 0.5 and 2.5 μg/L levels. Coefficients of determination R2≥0.9991 were achieved for each enantiomer in the soil and water matrix calibration curves within the range of 1.0-125 μg/L. The limits of detection (LOD) for all enantiomers in the soil and water were less than 0.8 μg/kg, whereas the limit of quantification (LOQ) did not exceed 2.5 μg/kg. The results of the method validation confirm that this proposed method is convenient and reliable for the enantioselective determination of the enantiomers of fenbuconazole and its main metabolites in soil and water.

Enantioselectivity in tebuconazole and myclobutanil non-target toxicity and degradation in soils

Tebuconazole and myclobutanil are two widely used triazole fungicides, both comprising two enantiomers with different fungicidal activity. However, their non-target toxicity and environmental behavior with respect to enantioselectivity have received limited attention. In the present study, tebuconazole and myclobutanil enantiomers were isolated and used to evaluate the occurrence of enantioselectivity in their acute toxicity to three non-target organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Significant differences were found: R-(-)-tebuconazole was about 1.4-5.9 times more toxic than S-(+)-tebuconazole; rac-myclobutanil was about 1.3-6.1 and 1.4-7.3 more toxic than (-)-myclobutanil and (+)-myclobutanil, respectively. Enantioselectivity was further investigated in terms of fungicide degradation in seven soil samples, which were selected to cover a broad range of soil properties. In aerobic or anaerobic soils, the S-(+)-tebuconazole degraded faster than R-(-)-tebuconazole, and the enantioselectivity showed a correlation with soil organic carbon content. (+)-Myclobutanil was preferentially degraded than (-)-myclobutanil in aerobic soils, whereas both enantiomers degraded at similar rates in anaerobic soils. Apparent correlations of enantioselectivity with soil pH and soil texture were observed for myclobutanil under aerobic conditions. In addition, both fungicides were configurationally stable in soils, i.e., no enantiomerization was found. Enantioselectivity may be a common phenomenon in both aquatic toxicity and biodegradation of chiral triazole fungicides, and this should be considered when assessing ecotoxicological risks of these compounds in the environment.

Simultaneous determination of pyrethrins residues in teas by ultra-performance liquid chromatography/tandem mass spectrometry.

A sensitive and effective method for the simultaneous quantitative determination of pyrethrin residues in teas was developed and validated using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The six major constituents of the pyrethrins (pyrethrin I and II, jasmolin I and II, and cinerin I and II) were successfully separated and independently confirmed in a single run within approximately 5 min. The multi-residue analysis of pyrethrins in teas involved simply extraction with acetonitrile, clean-up using a multilayer solid phase extraction cartridge, and subsequent separation by a hydrophilic end-capped Aquasil C18 columns with detection by tandem mass spectrometry using an electrospray ionization source in positive mode (ESI+). Recovery studies were carried out at three spiked levels (0.05, 0.1, 0.5 mg kg(-1)). The overall average recoveries using this method in green teas and black teas at the three concentration levels ranged from 76.15% to 101.86% with relative standard deviations (RSDs) in the range of 2.71-12.93% (n=5) for all analytes. The limits of detections (LODs) were below 0.009 mg kg(-1), which were lower than the maximum residue limits (MRLs) of 0.5 mg kg(-1) in tea samples established by the European Union legislations in 2008, while the limits of quantification (LOQ) did not exceed 0.03 mg kg(-1). This study provides a theoretical basis for China to draw up MRLs for pyrethrins in teas.

Environmental behavior of the chiral triazole fungicide fenbuconazole and its chiral metabolites: enantioselective transformation and degradation in soils.

Fenbuconazole is a widely used systemic agricultural fungicide of the triazole class with one chiral center. In the present study, the enantioselective degradation of fenbuconazole and its chiral metabolites, RH-9129 and RH-9130, in two soils under aerobic and anaerobic conditions were investigated using a chiral OD-RH column on a reversed-phase liquid chromatography-tandem mass spectrometry system. Under aerobic or anaerobic conditions, the results showed the occurrence of enantioselectivity with (-)-fenbuconazole preferentially degraded in both soils. Further enantioselective analysis of converted products showed that the concentrations of four RH-9129 and RH-9130 stereoisomers were different from each other under both aerobic and anaerobic conditions. The four stereoisomer concentrations followed the order (-)-RH-9129 > (+)-RH-9129 > (-)-RH-9130 > (+)-RH-9130 in Langfang alkaline soil. However, in the case of Changsha acidic soil, different RH-9129 and RH-9130 stereoisomer patterns were produced in the order (-)-RH-9129 > (+)-RH-9129 > (+)-RH-9130 > (-)-RH-9130. The (-)-RH-9129 stereoisomer had the highest concentration formed by transformation of fenbuconazole in both soils. The degradation of RH-9129 and RH-9130 in the two soils is also stereoselective under both aerobic and anaerobic conditions, the results indicating that the (+)-RH-9130 enantiomer degraded faster than the (-)-RH-9130 enantiomer and the (+)-RH-9129 enantiomer degraded faster than the (-)-RH-9129 enantiomer. In addition, the (-)-RH-9129 isomer exhibited the slowest degradation rate in both soils. This study provides the first experimental evidence of stereoselective degradation and transformation of fenbuconazole as well as its chiral metabolites in the environment.