Xiangyun Wang

Residue analysis and degradation studies of fenbuconazole and myclobutanil in strawberry by chiral high-performance liquid chromatography-tandem mass spectrometry.

A simple and sensitive enantioselective method for the determination of fenbuconazole and myclobutanil in strawberry was developed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Fenbuconazole and myclobutanil residues in strawberry were extracted with acetonitrile containing 1% acetic acid, and an aliquot was cleaned up with PSA (primary and secondary amine) and C(18) sorbent. The direct resolution of fenbuconazole and myclobutanil enantiomers was performed on a cellulose tris (3,5-dimethylphenylcarbamate) column using acetonitrile-0.1% formic acid solution (60:40, v/v) as the mobile phase. Quantification was achieved using matrix-matched standard calibration curves, and the limits of quantification for fenbuconazole and myclobutanil enantiomers in strawberry were both 2 μg/kg. The method was successfully utilized to investigate the probable enantioselective degradation of fenbuconazole and myclobutanil in strawberry. The results showed that the degradation of the fenbuconazole and myclobutanil enantiomers in strawberry followed pseudofirst-order kinetics (R(2) > 0.97). The results from this study revealed that the degradation of fenbuconazole in strawberry was not enantioselective, while the degradation of myclobutanil was enantioselective, and the (+)-myclobutanil showed a faster degradation than (-)-myclobutanil in strawberry, resulting in the relative enrichment of (-)-myclobutanil in residue. The results could provide a reference to fully evaluate the risks of these two fungicides.

Enantioselective degradation of tebuconazole in cabbage, cucumber, and soils

The enantioselective degradation of tebuconazole has been investigated to elucidate the behaviors in agricultural soils, cabbage, and cucumber fruit. Rac-tebuconazole was fortified into three types of agricultural soils and sprayed foliage of cabbage and cucumber, respectively. The degradation kinetics, enantiomer fraction and enantiomeric selectivity were determined by reverse-phase high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) on a Lux amylose-2 chiral column. The process of the degradation of tebuconazole enantiomers followed first-order kinetic in the test soils and vegetables. It has been shown that the degradation of tebuconazole was enantioselective. The results indicated that the (+)-S-tebuconazole showed a faster degradation in cabbage, while the (-)-R-tebuconazole dissipated faster than (+)-S-form in cucumber fruit and the test soils.

The toxicity of cadmium to three aquatic organisms (Photobacterium phosphoreum, Daphnia magna and Carassius auratus) under different pH levels

This study investigated the effect of pH on cadmium toxicity to three aquatic organisms: Photobacterium phosphoreum, Daphnia magna and Carassius auratus. The acute toxicity of Cd(2+) to P. phosphoreum and D. magna at five pH values (5.0, 6.0, 7.0, 8.0, and 9.0) was assessed by calculating EC50 values. We determined that Cd(2+) was least toxic under acidic conditions, and D. magna was more sensitive to the toxicity of Cd than P. phosphoreum. To evaluate Cd(2+)-induced hepatic oxidative stress in C. auratus at three pH levels (5.0, 7.25, 9.0), the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase), the level of glutathione and the malondialdehyde content in the liver were measured. Oxidative damage was observed after 7d Cd exposure at pH 9.0. An important finding of the current research was that Cd(2+) was generally more toxic to the three test organisms in alkaline environments than in acidic environments.

HPLC-MS/MS enantioseparation of triazole fungicides using polysaccharide-based stationary phases.

The enantiomeric separation of 21 triazole fungicides was carried out on four polysaccharide-derived chiral stationary phases in the reversed phase separation mode using high performance liquid chromatography coupled with tandem mass spectrometry. All fungicides were detected in electrospray ionization (ESI) positive mode with selected reaction monitoring (SRM). Complete enantioseparation was achieved for 21 fungicides except for difenoconazole based on cellulose tris (3,5-dimethylphenylcarbamate) and cellulose tris (3-chloro-4-methylphenyl carbamate) columns by optimizing experimental conditions including mobile phase and column temperature. Mobile phase was 0.1% formic acid aqueous solution mixed with methanol or acetonitrile in different proportions. Among all the fungicides, 15 with two enantiomers and three with four stereoisomers (bitertanol, bromuconazole, and cyproconazole) were successfully separated at 25°C. Enantioseparation for the other three fungicides (propiconazole, triadimenol, and difenoconazole) with four stereoisomers could be achieved by changing the column temperature from 10 to 40°C. Propiconazole and triadimenol were enantioseparated on baseline at 40 and at 35°C, respectively, and difenoconazole was enantioseparated partially with the R(s) > 1.1 at 25°C. Moreover, linearities and limits of detection (LODs) of 21 fungicides except for difenoconazole were studied, showing coefficients of determination (R(2)) higher than 0.99 and LODs lower than 2.5 μg/L.

Stereoselective determination of famoxadone enantiomers with HPLC‐MS/MS and evaluation of their dissipation process in spinach

A simple and enantioselective method for the determination of famoxadone enantiomers in spinach using reversed-phase HPLC-MS/MS is presented. Famoxadone residues in spinach were extracted with acetonitrile and an aliquot was cleaned up with PSA (primary and secondary amine, Si-(CH(2))(3)-NH-(CH(2))(2)-NH(2)) and C(18) sorbent, which were powder material. Chiral stationary phase (CSP), cellulose tris(3,5-dimethylphenylcarbamate), was successfully applied to separate two enantiomers using methanol/formic acid-ammonium acetate buffer as mobile phase. The MS/MS fragmentation pathway of ammonium adduct famoxadone molecules ion at m/z 392 was analyzed and an odd electron fragment ion at m/z 238 was observed. Excellent linearity was achieved for each enantiomer over a range of concentrations from 0.5 to 1500 μg/L with coefficients more than 0.99. Average recoveries at five different levels (1, 2.5, 12.5, 250 and 1250 μg/kg, for each enantiomer) ranged from 80.8 to 96.5% with RSD of 4.8-13.4%. The famoxadone enantiomers LODs in spinach were determined to be both 0.3 μg/kg with LOQs of 1 μg/kg. Based on this method, the dissipation process of famoxadone enantiomers in spinach under open field and greenhouse conditions was characterized, providing guidance to the proper and safe use of this fungicide in agriculture.

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

An enantioselective method is presented for the determination of isocarbophos in soil by liquid chromatography coupled with tandem mass spectrometry. The pesticide residues in soil samples were extracted with acetonitrile, and complete enantioseparation was obtained on an amylose tris(3,5-dimethylphenylcarbamate) chiral column using acetonitrile/2 mM ammonium acetate solution containing 0.1% formic acid (60:40, v/v) as the mobile phase. The absolute configuration of isocarbophos enantiomers was determined by the combination of experimental and calculated electronic circular dichroism spectra. The method was utilized to investigate the degradation of isocarbophos in soils (Changchun, Hangzhou, and Zhengzhou) under sterilized or native conditions. Isocarbophos enantiomers were configurationally stable in the selected soils, and the pesticide degradation was not enantioselective in the sterilized condition. The degradation behavior of rac-isocarbophos was different under native conditions, with no enantioselectivity in the Changchun soil and with the S-(+)-isocarbophos enriched in the Hangzhou and Zhengzhou soils.

Environmental behavior of the chiral organophosphorus insecticide acephate and its chiral metabolite methamidophos: enantioselective transformation and degradation in soils.

Acephate is a widely used organophosphorus insecticide globally, although there are some concerns about its usage with regard to acute consumer exposure and side-effects on nontarget organisms. These concerns are always attributed to the acephate metabolite methamidophos. In the many reports about the environmental behavior of acephate and its metabolite, none pay any attention to the chirality of them. In this study, the enantiomeric transformation and degradation of acephate was investigated in three soils under laboratory conditions using enantioselective GC-MS/MS. Racemic and enantiopure compounds were incubated in separate experiments. The degradation of racemates was shown to be enantioselective in unsterilized soils but not in the sterilized soils, thus confirming the enantioselectivity was microbially based. The priority of enantiomer degradation and transformation varied among soils and racemates. R-(+)-methamidophos was enriched in the Zhengzhou soil, but degraded faster in the Changchun and Nanchang soils than its antipode. For acephate, the Nanchang soil enriched R-(+)-acephate, and S-(-)-acephate accumulated in the other two soils. Acephate and methamidophos were both configurationally stable in soil, showing no interconversion of R-(+)- to S-(-)-enantiomers, or vice versa. The conversion of acephate to methamidophos proceeded with retention of configuration. Generally, the degradation followed approximate first-order kinetics, but showed significant lag phases.

Direct Chiral Determination of Acephate and Its Metabolite Methamidophos in Vegetables Using QuEChERS by Gas Chromatography–Tandem Mass Spectrometry

Currently, methamidophos, the main metabolite of acephate in the plants, has been paid particular attention in the risk evaluation of acephate because of its severely accurate toxicity, but the chirality of methamidophos and acephate has not been taken into account. In this study, a chiral separation and analysis method was developed to help evaluate the risks posing to the environment and human health. The efficiency of four commercial chiral capillary columns to accomplish enantioseparation of these two pesticides was firstly evaluated, and the chromatographic condition on the chose column BGB-176 SE was optimized. An analytical method for determination and confirmation of the enantiomers in vegetables by gas chromatography–tandem mass spectrometry was then developed with the column. QuEChERS was adopted to extract and clean the residues in vegetables. The mean recovery rates of quintuplicate results in cabbage and pakchoi ranged from 71.87 to 81.45xa0%; the relative standard deviation was less than 8.81xa0%. The limits of detection of enantiomers of acephate and methamidophos were 0.008 and 0.005xa0mg/kg, respectively. After the application of the method to vegetables from a market, it was proved that the metabolism of acephate and methamidophos in plants should be enantioselective.

Analysis of Tebuconazole and Tetraconazole Enantiomers by Chiral HPLC-MS/MS and Application to Measure Enantioselective Degradation in Strawberries

A rapid and sensitive enantioselective method for the determination of tebuconazole and tetraconazole enantiomers in strawberry has been developed. The enantiomers were resolved by high-performance liquid chromatography on a cellulose tris (3-chloro-4-methylphenylcarbamate) (Lux Cellulose-2) column using methanol–0.1% formic acid solution (70:30, v/v) as mobile phase. The chiral liquid chromatographic separation was combined with an extract/cleanup procedure known as the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. High-performance liquid chromatography-tandem mass spectrometry with electrospray ionization was then used for qualitative and quantitative determination of the enantiomers of tebuconazole and tetraconazole. Hexaconazole was used as an internal standard. The method provided high selectivity and sensitivity, and the limits of quantification for tebuconazole and tetraconazole enantiomers in strawberry were both 2.5xa0μg/kg. The method was successfully utilized to investigate the probable enantioselective degradation of tebuconazole and tetraconazole in strawberry. The results showed that the degradation of the tebuconazole and tetraconazole enantiomers in strawberry followed first-order kinetics (R2u2009>u20090.96). The results from this study revealed the degradation of tetraconazole in strawberry was not enantioselective, while the degradation of tebuconazole was enantioselective, and the (+)-tebuconazole showed a faster degradation than (−)-tebuconazole in strawberry. The results could provide a reference to fully evaluate risks of these two fungicides.

Enantioselective separation and simultaneous determination of fenarimol and nuarimol in fruits, vegetables, and soil by liquid chromatography–tandem mass spectrometry

AbstractA method for simultaneous enantioselective determination of fenarimol and nuarimol in apple, grape, cucumber, tomato, and soil was developed using liquid chromatography–tandem mass spectrometry. The enantioseparation results of the two fungicides through three different cellulose-based chiral columns are discussed. The influence of column temperature on the resolution of the enantiomers of the two fungicides was examined. Complete enantioseparation of the two fungicides’ enantiomers was obtained on a cellulose tris(4-methylbenzoate) column (Lux Cellulose-3) at 25xa0°C using methanol and 0.1xa0% formic acid solution (80:20, v/v) as mobile phase. The linearity, matrix effect, recovery, and precision were evaluated. Good linearity was obtained over the concentration range of 1–500xa0μgxa0L−1 for each enantiomer in the standard solution and sample matrix calibration solution. There was no significant matrix effect in apple, grape, cucumber, or tomato samples, but signal suppression was typically observed with the soil extracts. The mean recoveries, repeatability, and reproducibility were 76.5–103xa0%, 2.1–9.0xa0%, and 4.2–11.8xa0%, respectively. The limit of quantification for enantiomers of the two fungicides in fruits, vegetables and soil was 5xa0μgxa0kg−1. Moreover, the absolute configuration of the enantiomers of fenarimol and nuarimol was determined from a combination of experimentally determined and predicted electronic circular dichroism spectra.n FigurePredicted ECD spectra of nuarimol enantiomers (a) and fenarimol enantiomers (b). Experimentally measured ECD spectra of nuarimol enantiomers (c) and fenarimol enantiomers (d) in acetonitrile (20xa0mgxa0L−1)