Enantioselective analysis and degradation studies of isocarbophos in soils by chiral liquid chromatography-tandem mass spectrometry

In vitro profiling of pesticides within the Tox21 10K compound library for bioactivity and potential toxicity

Pesticides include a diverse class of toxic chemicals, often having numerous modes of actions when used in agriculture against targeted organisms to control insect infestation, halt unwanted vegetation, and prevent the spread of disease. In this study, the in vitro assay activity of pesticides within the Tox21 10K compound library were examined. The assays in which pesticides showed significantly more activities than non-pesticide chemicals revealed potential targets and mechanisms of action for pesticides. Furthermore, pesticides that showed promiscuous activity against many targets and cytotoxicity were identified, which warrant further toxicological evaluation. Several pesticides were shown to require metabolic activation, demonstrating the importance of introducing metabolic capacity to in vitro assays. Overall, the activity profiles of pesticides highlighted in this study can contribute to the knowledge gaps surrounding pesticide mechanisms and to the better understanding of the on- and off-target organismal effects of pesticides.

Dissecting the Enantioselective Neurotoxicity of Isocarbophos: Chiral Insight from Cellular, Molecular, and Computational Investigations

Chiral organophosphorus pollutants are found abundantly in the environment, but the neurotoxicity risks of these asymmetric chemicals to human health have not been fully assessed. Using cellular, molecular, and computational toxicology methods, this story is to explore the static and dynamic toxic actions and its stereoselective differences of chiral isocarbophos toward SH-SY5Y nerve cells mediated by acetylcholinesterase (AChE) and further dissect the microscopic basis of enantioselective neurotoxicity. Cell-based assays indicate that chiral isocarbophos exhibits strong enantioselectivity in the inhibition of the survival rates of SH-SY5Y cells and the intracellular AChE activity, and the cytotoxicity of (S)-isocarbophos is significantly greater than that of (R)-isocarbophos. The inhibitory effects of isocarbophos enantiomers on the intracellular AChE activity are dose-dependent, and the half-maximal inhibitory concentrations (IC₅₀) of (R)-/(S)-isocarbophos are 6.179/1.753 μM, respectively. Molecular experiments explain the results of cellular assays, namely, the stereoselective toxic actions of isocarbophos enantiomers on SH-SY5Y cells are stemmed from the differences in bioaffinities between isocarbophos enantiomers and neuronal AChE. In the meantime, the modes of neurotoxic actions display that the key amino acid residues formed strong noncovalent interactions are obviously different, which are related closely to the molecular structural rigidity of chiral isocarbophos and the conformational dynamics and flexibility of the substrate binding domain in neuronal AChE. Still, we observed that the stable "sandwich-type π-π stacking" fashioned between isocarbophos enantiomers and aromatic Trp-86 and Tyr-337 residues is crucial, which notably reduces the van der Waals' contribution (ΔG_vdW) in the AChE-(S)-isocarbophos complexes and induces the disparities in free energies during the enantioselective neurotoxic conjugations and thus elucidating that (S)-isocarbophos mediated by synaptic AChE has a strong toxic effect on SH-SY5Y neuronal cells. Clearly, this effort can provide experimental insights for evaluating the neurotoxicity risks of human exposure to chiral organophosphates from macroscopic to microscopic levels.

Fast detection of isocarbophos using bis-propargylcalix[4]arene-stabilized silver nanoparticles

Bis-propargylcalix[4]arene-stabilized silver nanoparticles (BPCA-Ag NPs), as a chemosensor for detecting an isocarbophos (ICP) pesticide in an aqueous medium, are reported in this work. The nanoparticles were characterized by UV-visible spectroscopy, dynamic light scattering, zeta potential and high-resolution transmission electron microscopy techniques. It was observed that the BPCA-Ag NPs had a high selectivity for isocarbophos with a detection limit of 1.0 × 10^-6 M. According to the result of this research, the BPCA-Ag NPs were found to be useful for the colorimetric detection of isocarbophos in an aqueous medium. It provides a new method for in situ detection of isocarbophos using host-guest interaction.

Rapid determination and dietary intake risk assessment of 249 pesticide residues in Panax notoginseng

UPLC-MS/MS and GC-MS/MS were used to establish a method to simultaneously determine various pesticide residues in Panax notoginseng. Results showed that the limits of detection of 249 pesticides were all 5-10 μg/kg. The detection rate of pesticides in 121 P. notoginseng samples was 93.39%, and 19 pesticides were detected. According to the US Code of Federal Regulations, the Chinese Pharmacopoeia recommended algorithm, and the Japanese "positive list system", the pass rates of pesticide residues were 100%, 99.17%, and 89.26%, respectively. The chronic risk quotient (ADI%) and acute risk quotient (ARfD%) of P. notoginseng were 0.00-0.12% and 0.00-0.15%, respectively. In summary, the detection method established in this study can be used for routine analysis of various P. notoginseng pesticide residues. The pesticide residues in the main root samples of P. notoginseng were at a safe level and unlikely pose health risks to consumers.

Old pesticide, new use: Smart and safe enantiomer of isocarbophos in locust control

Locust plagues are still worldwide problems. Selecting active enantiomers from current chiral insecticides is necessary for controlling locusts and mitigating the pesticide pollution in agricultural lands. Herein, two enantiomers of isocarbophos (ICP) were separated and the enantioselectivity in insecticidal activity against the pest Locusta migratoria manilensis (L. migratoria) and mechanisms were investigated. The significant difference of LD₅₀ between (+)-ICP (0.609 mg/kg bw) and (-)-ICP (79.412 mg/kg bw) demonstrated that (+)-ICP was a more effective enantiomer. The enantioselectivity in insecticidal activity of ICP enantiomers could be attributed to the selective affinity to acetylcholinesterase (AChE). Results of in vivo and in vitro assays suggested that AChE was more sensitive to (+)-ICP. In addition, molecular docking showed that the -CDOKER energies of (+)-ICP and (-)-ICP were 25.6652 and 24.4169, respectively, which suggested a stronger affinity between (+)-ICP and AChE. Significant selectivity also occurred in detoxifying enzymes activities (carboxylesterases (CarEs) and glutathione S-transferases (GSTs)) and related gene expressions. Suppression of detoxifying enzymes activities with (+)-ICP treatment suggested that (-)-ICP may induce the detoxifying enzyme-mediated ICP resistance. A more comprehensive understanding of the enantioselectivity of ICP is necessary for improving regulation and risk assessment of ICP.

Enantioselective degradation of the organophosphorus insecticide isocarbophos in Cupriavidus nantongensis X1T: Characteristics, enantioselective regulation, degradation pathways, and toxicity assessment

The chiral pesticide enantiomers often show selective efficacy and non-target toxicity. In this study, the enantioselective degradation characteristics of the chiral organophosphorus insecticide isocarbophos (ICP) by Cupriavidus nantongensis X1^T were investigated systematically. Strain X1^T preferentially degraded the ICP R isomer (R-ICP) over the S isomer (S-ICP). The degradation rate constant of R-ICP was 42-fold greater than S-ICP, while the former is less bioactive against pest insects but more toxic to humans than the latter. The concentration ratio of S-ICP to R-ICP determines whether S-ICP can be degraded by strain X1^T. S-ICP started to degrade only when the ratio (C_S-ICP/C_R-ICP) was greater than 62. Divalent metal cations could improve the degradation ability of strain X1^T. The detected metabolites that were identified suggested a novel hydrolysis pathway, while the hydrolytic metabolites were less toxic to fish and green algae than those from P-O bond breakage. The crude enzyme degraded both R-ICP and S-ICP in a similar rate, indicating that enantioselective degradation was due to the transportation of strain X1^T. The strain X1^T also enantioselectively degraded the chiral organophosphorus insecticides isofenphos-methyl and profenofos. The enantioselective degradation characteristics of strain X1^T make it suitable for remediation of chiral organophosphorus insecticide contaminated soil and water.

Development and Validation of Multiclass Chiral Pesticide Residues Analysis Method in Tea by QuEChERS Combined Liquid Chromatography Quadruple-Linear Ion Trap Mass Spectrometry

BACKGROUND

No single pure enantiomeric pesticide residues was investigated and set regulations for tea quality safety and risk assessment.

OBJECTIVE

Due to lack of chiral pesticide analysis method and data, the Maximum residue limits (MRLs) about the chiral pesticides in tea was unknown.

METHOD

An analytical method for the determination of chiral pesticide residues by QuEChERS combined chiral liquid chromatography quadruple/linear ion trap mass spectrometry (LC-MS/MS-Qtrap) was developed and applied to the analysis of various teas.

RESULTS

The mean recoveries for pesticides enantiomers ranged from 75.9% to 112.4%. Reproducibility represented by relative standard deviation percentage was 10% or less. Good linearity was achieved for all enantiomers with determination coefficients (r2) greater than 0.99. The detection of limit (CCα) and quantification of limit (CCβ) were 0.2 ∼1 µg/kg and 0.5∼5 µg/kg, respectively.

CONCLUSIONS

The method was suitable for monitoring the enantiomeric pesticide residues in various teas.

HIGHLIGHTS

Enantioselective multiclass pesticide residues were determined in various teas by LC-MS/MS-Qtrap, additional Qtrap scan functions greatly enhance the performance of screening, confirmation, and identification of chiral pesticides.

Enantioselective behaviors of cis-epoxiconazole in vegetables-soil-earthworms system by liquid chromatography-quadrupole-time-of-flight mass spectrometry

Cis-epoxiconazole is a widely used triazole fungicide for control and prevention of a series of fungal diseases in fruits, vegetables, teas and grains. The present work aimed at exploring enantioselective behavior of cis-epoxiconazole in the vegetable-soil-earthworm system. Firstly, the absolute configuration of cis-epoxiconazole enantiomers was ascertained. Secondly, enantioselective degradation of cis-epoxiconazole in cabbage, pakchoi and pepper were performed under field trials, which has not been previously reported. Enantioselective degradation occurred in cabbage and pepper samples. 2R, 3S-(+)-cis-epoxiconazole was degraded faster than 2S, 3R-(-)-cis-epoxiconazole in cabbage, while the reversed results were obtained in pepper. No enantioselective degradation was observed in pakchoi. Finally, soil is the principal reservoir of environmental pesticides, so the enantioselective behaviors of cis-epoxiconazole in soil and soil organism (earthworm, Eisenia fetida) were evaluated. Similar bioaccumulation curves in earthworms and degradation curves in soil were observed under the exposure levels of 1 and 10 mg/kg. Accumulation factors (AFs) indicated earthworms had weak bioaccumulation potential to cis-epoxiconazole in the contaminated soil, and no obvious enantioselectivity was observed. The different enantioselectivities in different vegetables illuminated that preferentially enriched enantiomer might impose higher risk on human health than the other one, and the high risk enantiomer required further assessment. These results may reduce the uncertainty of cis-epoxiconazole to the environmental risk assessment.

Dual-modal aptasensor for the detection of isocarbophos in vegetables

An aptamer-based colorimetric-phosphorescent assay was developed for the detection of isocarbophos. The colorimetric assay relied on the aggregation of gold nanoparticles (AuNPs) caused by the competitive binding of aptamer between isocarbophos and AuNPs in the presence of a high salt concentration. The further addition of persistent luminescence nanorods (PLNRs) into the system showed the phosphorescence sensitively proportional to the concentration of isocarbophos, due to the inner filter effect between PLNRs and AuNPs. The assay showed good linearity within 50-500 μg/L and 5-160 μg/L, and limit of detection of 7.1 μg/L and 0.54 μg/L in colorimetry and phosphorescence mode, respectively. The feasibility of this approach for food analysis was demonstrated with the sensitive and selective determination of isocarbophos residues in vegetables.

Comprehensive Study of Isocarbophos to Various Terrestrial Organisms: Enantioselective Bioactivity, Acute Toxicity, and Environmental Behaviors

The enantioselective bioactivity, toxicity, and environmental behaviors of isocarbophos (ICP) were investigated. The order of the bioactivity and toxicity was S-(+) ≥ rac > R-(-), and the difference of R-(-) and S-(+) was up to 232 times. The usage of S-(+)-ICP may efficiently reduce the usage amount of rac-ICP by 35% under the same effect, and the toxicity was not increased. Based on the toxic unit analysis, the additive effect and synergistic effect of ICP enantiomers were found in the four nontarget organisms, and R-(-)-ICP might cooperate the side-effects of S-(+)-ICP. The accumulation of rac-ICP in earthworms was enantioselective with an enantioenrichment of R-(-)-ICP, so the usage of racemic ICP might increase the exposure risk of R-(-)-ICP to earthworms. From the comprehensive results, the production of enantiomer enriched S-(+)-ICP might increase bioactivity and reduce environmental pollution, while the toxicity of S-(+)-ICP to other nontarget organisms needs to be further assessed.

A systemic study of enantioselectivity of isocarbophos in rice cultivation: Enantioselective bioactivity, toxicity, and environmental fate

The enantioselective bioactivity and acute toxicity to target and non-target model species, and environmental fate of isocarbophos (ICP) in rice cultivation were investigated systematically. Bioactivity and toxicity of S-(+)-ICP was significantly greater than R-(-)-ICP, and the difference was 2.9-101 times. Based on the toxic unit analysis, the toxic interaction of ICP enantiomers for target pests was synergistic effect, while for non-target fish was concentration addition or antagonistic effect. Rac-ICP displayed equivalent bioactivity to S-(+)-ICP under the equal dosage, but the toxicity of rac-ICP to the tested fishes reduced at least 2 times. Rac-ICP is more suitable than optically pure S-(+)-ICP for rice cultivation based on the toxicity and bioactivity results. In environmental behavior experiments, the main metabolite of ICP, isocarbophos oxon (ICPO) was detected in rice plants, water, rice and rice hull samples. S-(+)-ICP and S-(+)-ICPO were more persistent than the R-form in these matrices. The comprehensive data of ICP enantiomers in rice cultivation will improve environmental and ecological risk assessment, and using racemate may be more safe and reasonable in rice cultivation system.

A potential biomarker of isofenphos-methyl in humans: A chiral view

Isofenphos-methyl (IFP) is a very active and persistent chiral insecticide. However, IFP has lower activity against acetylcholinesterases (AChEs). Previously, it was confirmed that phosphorothioate organophosphorus pesticides with N-alkyl (POPN) require activation by oxidative desulfuration and N-dealkylation. In this work, we demonstrated that IFP could be metabolized in human liver microsomes to isofenphos-methyl oxon (IFPO, 52.7%), isocarbophos (ICP, 14.2%) and isocarbophos oxon (ICPO, 11.2%). It was found that (R)-IFP was preferentially degraded compared to the (S)-enantiomer, and the enantiomeric fraction (EF) value reached 0.61 at 60 min. However, (S)-enantiomers of the three metabolites, were degraded preferentially, and the EF values ranged from 0.34 to 0.45. Cytochrome P450 (CYP) isoforms CYP3A4, CYP2E1, and CYP1A2 and carboxylesterase enzyme have an essential role in the enantioselective metabolism of IFP; but, the enzymes that participate in the degradation of IFP metabolites are different. The AChE inhibition bioassay indicated that ICPO is the only effective inhibitor of AChE. The covalent molecular docking has proposed that the metabolites of IFP and its analogs after N-dealkylation and oxidative desulfuration will possess the highest inhibitory activity against AChE. This study is the first to demonstrate that ICPO can be regarded as a potential biomarker for the biomonitoring of IFP and ICP exposure in humans.

Stereoselective degradation behaviour of carfentrazone-ethyl and its metabolite carfentrazone in soils

The stereoselective environmental behaviour of carfentrazone-ethyl and its metabolite carfentrazone enantiomer in three types of soil were studied under aerobic conditions. Under aerobic conditions, significant stereoselective difference in the degradation behaviour of carfentrazone-ethyl and its metabolite carfentrazone enantiomer was observed in Jiangxi red soil, Jilin black soil and Anhui paddy soil. The EF values of the carfentrazone-ethyl enantiomers in Anhui paddy soil, Jilin black soil, and Jiangxi red soil were 0.67, 0.65 and 0.57, respectively. The EF values of the carfentrazone enantiomer in the three types of soil were 0.75, 0.80 and 0.76. No bidirectional chiral inversion of enantiopure carfentrazone-ethyl and carfentrazone enantiomers was observed in Jilin soil. As a result, R-(+)-carfentrazone-ethyl and S-(+)-carfentrazone in soil would be preferentially degraded, while S-(-)-carfentrazone-ethyl and R-(-)-carfentrazone were enriched. The results found in this paper could provide more scientific guidance for the risk assessments of carfentrazone-ethyl from a chiral perspective.

Enantioselective degradation and transformation of the chiral fungicide prothioconazole and its chiral metabolite in soils

Prothioconazole is a widely used chiral triazole fungicide. In this work, the enantioselective degradation and transformation of prothioconazole and its chiral metabolite prothioconazole-desthio in five kinds of soils were investigated under native and sterile conditions using reversed phase liquid chromatography tandem mass spectrometry with a Lux-cellulose-1 column. The results showed that an enantioselective degradation was observed with R-prothioconazole preferentially degraded in the five soils and enantiomeric fraction values that ranged from 0.32 to 0.41 under native conditions. Furthermore, the major metabolite prothioconazole-desthio was formed rapidly during prothioconazole dissipation. The prothioconazole-desthio enantiomers were degraded slowly, and there was a slight enantioselectivity with enantiomeric fraction values that ranged from 0.45 to 0.51 in the Nanjing and Jilin soils. Under sterile conditions, prothioconazole and its metabolite enantiomers were more slowly degraded with no enantioselectivity. The result of the incubation experiment with single enantiomers verified that R- and S-prothioconazole were transformed to R- and S-prothioconazole-desthio, respectively. No enantiomerization for prothioconazole and its chiral metabolite was observed. In addition, the excellent correlation between organic matter content and degradation rate indicated that organic matter could promote the degradation of prothioconazole and its metabolite enantiomers. The data in this study provide the experimental evidence of the stereoselective degradation and metabolism of both prothioconazole and its chiral metabolite in the environment.

Enantioselective analysis and degradation of isofenphos-methyl in vegetables by liquid chromatography-tandem mass spectrometry

The enantioselective degradation of isofenphos-methyl in cowpea, cucumber, and pepper under field conditions was investigated to elucidate the enantioselective environmental behaviors of this pesticide. The concentrations of the enantiomers were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The degradation rates of isofenphos-methyl enantiomers were the fastest in cowpea, followed by cucumber and pepper, with half-lives ranging from 1.48 to 8.06 days. The enantioselective degradation of isofenphos-methyl was characterized by calculating and comparing the values of enantiomer fraction (EF) and enantiomeric selectivity (ES). The degradation rates and enantioselectivities of isofenphos-methyl were different for the three vegetables. (R)-(-)-isofenphos-methyl was degraded faster than (S)-(+)-isofenphos-methyl in cowpea and cucumber, whereas (S)-(+)-isofenphos-methyl underwent preferential degradation in pepper. These results could serve as a reference for the study of enantioselective behavior of isofenphos-methyl in plants and further food safety evaluation, where the enantiomeric differences should be considered in the risk assessment.

Simultaneous Enantioselective Determination of the Chiral Fungicide Prothioconazole and Its Major Chiral Metabolite Prothioconazole-Desthio in Food and Environmental Samples by Ultraperformance Liquid Chromatography-Tandem Mass Spectrometry

An efficient and sensitive chiral analytical method was established for the determination of the chiral fungicide prothioconazole and its major chiral metabolite prothioconazole-desthio in agricultural and environmental samples using ultraperformance liquid chromatography-tandem mass spectrometry. The optical rotation and absolute configuration of enantiomers were identified by optical rotation detector and electronic circular dichroism spectra. The elution order of prothioconazole and its chiral metabolite enantiomers was R-(+)-prothioconazole-desthio, S-(-)-prothioconazole-desthio, R-(-)-prothioconazole, and S-(+)-prothioconazole. The mean recoveries from the samples was 71.8-102.0% with intraday relative standard deviations (RSDs) of 0.3-11.9% and interday RSDs of 0.9-10.6%. The formation of prothioconazole-desthio was studied in soil under field conditions and enantioselective degradation was observed for chiral prothioconazole. Remarkable enantioselective degradation was observed: R-prothioconazole degraded preferentially with EF values from 0.48 to 0.37. Although prothioconazole-desthio is the most remarkably bioactive metabolite, no obvious enantioselective behavior was observed in soil. These results may help to systematically evaluate prothioconazole and its metabolites in food and environmental safety.

Validation of a Chiral Liquid Chromatographic Method for the Degradation Behavior of Flumequine Enantiomers in Mariculture Pond Water

In this work, flumequine (FLU) enantiomers were separated using a Chiralpak OD-H column, with n-hexane-ethanol (20:80, v/v) as the mobile phase at a flow rate of 0.6 mL/min. Solid phase extraction (SPE) was used for cleanup and enrichment. The limit of detection, limit of quantitation, linearity, precision, and intra/interday variation of the chiral high-performance liquid chromatography (HPLC) method were determined. The developed method was then applied to investigate the degradation behavior of FLU enantiomers in mariculture pond water samples. The results showed that the degradation of FLU enantiomers under natural, sterile, or dark conditions was not enantioselective. Chirality 28:649-655, 2016. © 2016 Wiley Periodicals, Inc.

Enantioseparation and determination of the chiral phenylpyrazole insecticide ethiprole in agricultural and environmental samples and its enantioselective degradation in soil

An effective method for the enantioselective determination of ethiprole enantiomers in agricultural and environmental samples was developed. The effects of solvent extraction, mobile phase and thermodynamic parameters for chiral recognition were fully investigated. Complete enantioseparation of the ethiprole enantiomers was achieved on a Lux Cellulose-2 column. The stereochemical structures of ethiprole enantiomers were also determined, and (R)-(+)-ethiprole was first eluted. The average recoveries were 82.7-104.9% with intra-day RSD of 1.7-8.2% in soil, cucumber, spinach, tomato, apple and peach under optimal conditions. Good linearity (R(2)≥0.9991) was obtained for all the matrix calibration curves within a range of 0.1 to 10 mg L(-1). The limits of detection for both enantiomers were estimated to be 0.008 mg kg(-1) in soil, cucumber, spinach and tomato and 0.012 mg kg(-1) in apple and peach, which were lower than the maximum residue levels established in Japan. The results indicate that the proposed method is convenient and reliable for the enantioselective detection of ethiprole in agricultural and environmental samples. The behavior of ethiprole in soil was studied under field conditions and the enantioselective degradation was observed with enantiomer fraction values varying from 0.494 to 0.884 during the experiment. The (R)-(+)-ethiprole (t1/2=11.6 d) degraded faster than (S)-(-)-ethiprole (t1/2=34.7 d). This report is the first describe a chiral analytical method and enantioselective behavior of ethiprole, and these results should be extremely useful for the risk evaluation of ethiprole in food and environmental safety.

Bioaccumulation of isocarbophos enantiomers from laboratory-contaminated aquatic environment by tubificid worms

The benthic fauna is of great importance to assess the environmental fate of contaminations in aquatic ecosystem. In this study, tubificids were exposed to both laboratory-contaminated aqueous phases and spiked sediment to study the bioaccumulation of isocarbophos (ICP). Two types of spiked sediments were used in the spiked sediment experiment. During the exposure period, an enantioselective bioaccumulation was found in spiked water treatment, with concentrations of the (-)-ICP higher than that of the (+)-ICP, but no enantioselectivity was detected in the spiked sediment treatments. However, different bioaccumulation patterns were observed in the two spiked sediment treatments. Results showed that for spiked forest field sediment (FF sediment) incubation, bioaccumulation was governed by the concentrations in soil. Whereas ICP was bioaccumulated dominantly from overlying water in spiked Chagan Lake sediment (CG sediment) test. The dissipation rates were proved different in the two sediments and ICP dissipated much faster in CG sediment than that in FF sediment. Significant difference in ICP's half-life was also observed between worm-present and worm-free treatments in FF sediment. The detections of concentrations in overlying water indicated that much more ICP diffused to aquatic phase with the present of tubificids.

Simultaneous determination of florfenicol with its metabolite based on modified quick, easy, cheap, effective, rugged, and safe sample pretreatment and evaluation of their degradation behavior in agricultural soils

A simple and simultaneous method for the determination of florfenicol and its metabolite florfenicol amine in agricultural soils using modified quick, easy, cheap, effective, rugged, and safe sample pretreatment and reversed-phase high-performance liquid chromatography with tandem mass spectrometry is presented. Florfenicol and its metabolite florfenicol amine residues in agricultural soils were extracted with alkalized acetonitrile and an aliquot was cleaned up with Si(CH2)3NH(CH2)2NH2 and C18 sorbent, which were powder materials. High-performance liquid chromatography with tandem mass spectrometry was applied to simultaneously determine the level of florfenicol and florfenicol amine in agricultural soils. Excellent linearity was achieved for florfenicol and florfenicol amine over a range of concentrations from 0.1-500 μg/L with coefficients more than 0.99. Average recoveries at four different levels (0.005, 0.05, 0.5, and 5.0 mg/kg) for florfenicol and florfenicol amine ranged from 73.6-94.9% with relative standard deviations of 2.9-12.5%. The limits of detection for florfenicol and florfenicol amine in agricultural soils were 2.0 μg/kg, and the limits of quantification were 6.0 μg/kg. Based on this method, the degradation behavior of florfenicol and its metabolite florfenicol amine in three soils (Nanchang, Hangzhou, and Changchun) under sterilized and native conditions was investigated and the transformation rate of florfenicol amine from florfenicol was evaluated.

Simultaneous enantioselective determination of triazole fungicide flutriafol in vegetables, fruits, wheat, soil, and water by reversed-phase high-performance liquid chromatography

A novel and effective method for enantioselective determination of flutriafol enantiomers in food and environmental matrices (cucumber, tomato, grape, pear, wheat, soil, and water) has been developed. The (R)-(-)-flutriafol was first eluted and measured from electronic circular dichroism spectra using a cellulose tris(3-chloro-4-methyl phenyl carbamate) chiral column. The mean recoveries from the samples ranged from 82.9% to 103.4%, with intraday relative standard deviations (RSD) of 2.2-8.3% and interday RSD of 3.4-7.9%. Good linearity (R(2) ≥ 0.9989) was obtained for all analytes matrix calibration curves within the range of 0.1-10 mg/kg. The limits of detection for two enantiomers in the seven matrices were all below 0.015 mg/kg. The results show that the proposed method is convenient and reliable for the enantioselective detection of the flutriafol in the real samples and is applicable to the environmental stereochemistry of flutriafol in food and environmental matrices.

Enantiomeric separation of indoxacarb on an amylose-based chiral stationary phase and its application in study of indoxacarb degradation in water

Direct semipreparative enantioseparation of indoxacarb was performed on a semipreparative Chiralpak IA column using normal-phase high-performance liquid chromatography (HPLC) with n-hexane-isopropanol-ethyl acetate (70:20:10) mixture as mobile phase. Degradation of indoxacarb (2.33S + 1R) and its two enantiopure isoforms in three aqueous buffer solutions and four water samples collected from natural water sources was then elucidated by HPLC analysis on Chiralpak IA column. Degradation of all three indoxacarbs complied with first-order kinetics and demonstrated linearity with regression coefficients R(2) > n0.88. Indoxacarb (2.33S + 1R) underwent enantioselective degradation in river water, rain water, and buffer solution of pH 7.0. Enantiopure S-(+)-indoxacarb and R-(-)-indoxacarb were both found to be configurationally stable in water.