Zenglong Chen

Green and sensitive supercritical fluid chromatographic-tandem mass spectrometric method for the separation and determination of flutriafol enantiomers in vegetables, fruits, and soil.

A green and sensitive chiral analytical method was developed to determine flutriafol enantiomers in vegetables (tomato, cucumber), fruits (apple, grape), and soil by supercritical fluid chromatography-tandem mass spectrometry. The enantioseparation was performed within 3.50 min using Chiralpak IA-3 column with CO2/methanol (88:12, v/v) as the mobile phase at a 2.2 mL/min flow rate. The postcolumn compensation technology provided with 1% formic acid/methanol greatly improved the ionization efficiency of mass spectrometry. Column temperature, auto back pressure regulator pressure, and flow rate of compensation solvent were optimized to 30 °C, 2200 psi, and 0.1 mL/min, respectively. The simple and fast QuEChERS pretreatment method was adopted. Mean recoveries for flutriafol enantiomers were 77.2-98.9% with RSDs ≤ 9.6% in all matrices. The limits of quantification ranged from 0.41 to 1.18 μg/kg. Well-applied to analyze authentic samples, the developed method could act as a versatile strategy for the analysis of flutriafol enantiomers in food and environmental matrices.

Stereoselective analysis of novel chiral fungicide pyrisoxazole in cucumber, tomato and soil under different application methods with supercritical fluid chromatography/tandem mass spectrometry.

Various new chiral pesticides have been registered and used in crop yields. However, few studies have focused on the environmental behavior of such new registered chiral compounds on the stereoisomer level. In this study, an effective and sensitive chiral analytical method was first developed to detect pyrisoxazole stereoisomers and then further applied to investigate the stereoselective dissipation in vegetables and soil using supercritical fluid chromatography/tandem triple quadrupole mass spectrometry. Optimal separation condition was achieved with IA column using CO2/MeOH (75:25) as mobile phase at 2.0 mL/min in 5 min, 35 °C and 2400 psi. The average recoveries in all of the matrices at four spiking levels ranged from 84.0% to 105.6%. Significant stereoselective dissipation was observed in cucumber and tomato under both application modes. (-) Pyrisoxazole A and (-) pyrisoxazole B were preferentially degraded in cucumber under foliar spraying mode. In contrast, (+) pyrisoxazole A and (-) pyrisoxazole B were preferentially degraded in cucumber under soil irrigation mode. (-) Pyrisoxazole A and (-) pyrisoxazole B were degraded faster than their antipodes in tomato under both application modes. However, no significant stereoselectivity was observed in soil. The results of this study could help facilitate more accurate risk assessments of pyrisoxazole.

Simultaneous determination of fipronil and its major metabolites in corn and soil by ultra-performance liquid chromatography-tandem mass spectrometry

A simple, quick, effective method was developed for the determination of fipronil and its three metabolites in soil and corn by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Samples were extracted with acetonitrile and cleaned-up with C18, C18/PSA, PSA/GCB for soil, corn grain, and corn straw, respectively. The optimization of MS/MS parameters was performed in multi-reaction monitoring (MRM) mode, and electrospray ionization (ESI) in the negative mode was selected. The mean recoveries of the four compounds in soil, corn grain, and corn straw matrices at four fortification levels were in the range of 82.4% to 104.6%; the intra-day and inter-day RSDs ranged from 1.2% to 7.7% and 2.4% to 9.4%, respectively. The LODs of fipronil and its three metabolites in soil, corn grain, and corn straw matrices were estimated to be 0.5–2.5 μg kg−1, the LOQs were 5 μg kg−1 for soil and corn grain, and 10 μg kg−1 for corn straw. The developed method was also applied to the study of fipronil dissipation in soil and corn. The results further confirmed the reliability and efficacy of the proposed method for routine pesticide residue monitoring in soil and corn samples.

Response surface methodology for the enantioseparation of dinotefuran and its chiral metabolite in bee products and environmental samples by supercritical fluid chromatography/tandem mass spectrometry.

Tracing the enantiomers of dinotefuran and its metabolite in bee products and relevant environmental matrices is vital because of the high toxicity of their racemates to bees. In this study, a statistical optimization strategy using three-dimensional response surface methodology for the enantioseparation of dinotefuran and its metabolite UF was developed by a novel supercritical fluid chromatography/tandem mass spectrometry (SFC-MS/MS) technique. After direct evaluation of the chromatographic variables - co-solvent content, mobile phase flow rate, automated backpressure regulator pressure (ABPR), and column temperature - involved in the separation mechanism and assessment of the interactions among these variables, the optimal SFC-MS/MS working conditions were selected as a CO2/2% formic acid-methanol mobile phase, 1.9mL/min flow rate, 2009.8psi ABPR, and 26.0°C column temperature using an amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase under electrospray ionization positive mode. Baseline resolution, favorable retention, and high sensitivity of the two pairs of enantiomers were achieved in pollen, honey, water, and soil matrices within 4.5min. Additionally, the parameters affecting the dispersive solid-phase extraction procedure, such as the type and content of extractant or purification sorbents, were systematically screened to obtain better extraction yields of the enantiomers. Mean recoveries were between 78.3% and 100.2% with relative standard deviations lower than 8.0% in all matrices. The limits of quantification ranged from 1.0μg/kg to 12.5μg/kg for the dinotefuran and UF enantiomers. Furthermore, the developed method was effectively applied to authentic samples from a market, an irrigation canal, and a trial field, and the enantioselective dissipation of dinotefuran and UF in soil was demonstrated.

Stereoselective Determination of Tebuconazole in Water and Zebrafish by Supercritical Fluid Chromatography Tandem Mass Spectrometry.

A simple and sensitive method for the enantioselective determination of tebuconazole enantiomers in water and zebrafish has been established using supercritical fluid chromatography (SFC)-MS/MS. The effects of the chiral stationary phases, mobile phase, auto back pressure regulator (ABPR) pressure, column temperature, flow rate of the mobile phase, and compensation pump solvent were evaluated. Finally, the optimal SFC-MS/MS working conditions were determined to include a CO2/MeOH mobile phase (87:13, v/v), 2.0 mL/min flow rate, 2200 psi ABPR, and 30 °C column temperature using a Chiralpak IA-3 chiral column under electrospray ionization positive mode. The modified QuEChERS method was applied to water and zebrafish samples. The mean recoveries for the tebuconazole enantiomers were 79.8-108.4% with RSDs ≤ 7.0% in both matrices. The LOQs ranged from 0.24 to 1.20 μg/kg. The developed analytical method was further validated by application to the analysis of authentic samples.

Enantioselective separation and pharmacokinetic dissipation of cyflumetofen in field soil by ultra‐performance convergence chromatography with tandem mass spectrometry

Little data on the enantioselective separation of cyflumetofen exists, despite the fact that such data are essential to the assessment of the fate and potential toxic effects of cyflumetofen enantiomers. To address this issue, a simple and sensitive method for the enantioselective determination of cyflumetofen enantiomers in soil has been established using ultra performance convergence chromatography tandem triple quadrupole mass spectrometry. The effects of the chiral stationary phases, mobile phase, auto backpressure regulator pressure, column temperature, flow rate of the mobile phase, and compensation pump solvent were evaluated. The proposed method was applied to the study of the pharmacokinetic dissipation of cyflumetofen stereoisomers in soil under greenhouse conditions. The estimated half-life of cyflumetofen isomers ranged from 12.2 to 13.6 days, and statistically significant enantioselective degradation was observed. This study not only demonstrates that there is an efficient and sensitive method for cyflumetofen enantioseparation, but also provides the first experimental evidence of the pharmacokinetic dissipation of cyflumetofen stereoisomers in the environment.

Enantioseparation and determination of isofenphos-methyl enantiomers in wheat, corn, peanut and soil with Supercritical fluid chromatography/tandem mass spectrometric method

Supercritical fluid chromatography/tandem mass spectrometry (SFC-MS/MS) is an effective tool in separation science which uses the nontoxic CO2 fluid for better control of analyte retention. Also the technology of a postcolumn additive to complement MS/MS ensure the high-selectivity determination. In this paper, a green and sensitive analytical method was developed for the enantioselective separation and determination of isofenphos-methyl enantiomers in foodstuff and soil by SFC-MS/MS. The enantioseparation was performed within 3.50 min using Chiralpak IA-3 column with CO2/isopropanol (90:10, v/v) as the mobile phase at 2.2 mL/min flow rate. The postcolumn compensation technology provided with 0.1% formic acid/methanol greatly improved the ionization efficiency of mass spectrometry. Column temperature, auto back pressure regulator pressure, and flow rate of compensation solvent were optimized to 30 °C, 2200 psi, and 0.1 mL/min, respectively. The QuEChERs method was adopted in this study, which mean recoveries of isofenphos-methyl enantiomers ranged from 75.7% to 111.4%, with relative standard deviations less than 11.3% at three concentration levels in all matrices. The limits of detection for both enantiomers varied from 0.02 μg/kg to 0.15 μg/kg, while the limit of quantification did not exceed 0.50 μg/kg. The proposed method was then successfully applied to analyze authentic samples, confirming that it was a versatile strategy for the analysis of isofenphos-methyl enantiomers in food and environmental matrices.

Simultaneous determination of organophosphorus pesticides in fruits and vegetables using atmospheric pressure gas chromatography quadrupole-time-of-flight mass spectrometry

This paper describes the application of atmospheric pressure gas chromatography quadrupole-time-of-flight mass spectrometry for the simultaneous determination of organophosphorus pesticides in apple, pear, tomato, cucumber and cabbage. Soft ionization with atmospheric pressure ionization source was compared with traditional electron impact ionization (EI). The sensitivity of GC coupled to atmospheric pressure ionization (APGC) for all the analytes was enhanced by 1.0-8.2 times. The ionization modes with atmospheric pressure ionization source was studied by comparing the charge-transfer and proton-transfer conditions. The optimized QuEChERs method was used to pretreat the samples. The calibration curves were found linear from 10 to 1000μg/L, obtaining correlation coefficients higher than 0.9845. Satisfactory mean recovery values, in the range of 70.0-115.9%, and satisfactory precision, with all RSDr <19.7% and all RSDR values <19.5% at the three fortified concentration levels for all the fifteen OPPs. The results demonstrate the potential of APGC-QTOF-MS for routine quantitative analysis of organophosphorus pesticide in fruits and vegetables.

Atmospheric pressure gas chromatography quadrupole-time-of-flight mass spectrometry for simultaneous determination of fifteen organochlorine pesticides in soil and water.

In this study, the application of atmospheric pressure gas chromatography quadrupole-time-of-flight mass spectrometry (APGC-QTOF-MS) has been investigated for simultaneous determination of fifteen organochlorine pesticides in soil and water. Soft ionization of atmospheric pressure gas chromatography was evaluated by comparing with traditional more energetic electron impact ionization (EI). APGC-QTOF-MS showed a sensitivity enhancement by approximately 7-305 times. The QuEChERs (Quick, Easy, Cheap, Effective, Rugged, and Safe) method was used to pretreat the soil samples and solid phase extraction (SPE) cleanup was used for water samples. Precision, accuracy and stability experiments were undertaken to evaluate the feasibility of the method. The results showed that the mean recoveries for all the pesticides from the soil samples were 70.3-118.9% with 0.4-18.3% intra-day relative standard deviations (RSD) and 1.0-15.6% inter-day RSD at 10, 50 and 500 μg/L levels, while the mean recoveries of water samples were 70.0-118.0% with 1.1-17.8% intra-day RSD and 0.5-12.2% inter-day RSD at 0.1, 0.5 and 1.0 μg/L levels. Excellent linearity (0.9931 ≦ r(2)≤ 0.9999) was obtained for each pesticides in the soil and water matrix calibration curves within the range of 0.01-1.0mg/L. The limits of detection (LOD) for each of the 15 pesticides was less than 3.00 μg/L, while the limit of quantification (LOQ) was less than 9.99 μg/L in soil and water. Furthermore, the developed method was successfully applied to monitor the targeted pesticides in real soil and water samples.

A quick, easy, cheap, effective, rugged, and safe method for the simultaneous detection of four triazolone herbicides in cereals combined with ultrahigh performance liquid chromatography with tandem mass spectrometry

This paper describes a novel, rapid, and sensitive analytical method for monitoring four triazolone herbicides in cereals (wheat, rice, corn, and soybean), using a quick, easy, cheap, effective, rugged, and safe sample extraction procedure followed by ultrahigh performance liquid chromatography coupled with tandem mass spectrometry. The four triazolone herbicides (amicarbazone, carfentrazone-ethyl, sulfentrazone, and thiencarbazone-methyl) were extracted using acidified acetonitrile (containing 1% v/v formic acid) and subsequently purified with octadecylsilane (C18 ) prior to sample analysis. Ultrahigh performance liquid chromatography coupled with tandem mass spectrometry was operated in positive and negative ionization switching mode. Amicarbazone and carfentrazone-ethyl were detected in the positive mode (ESI+), while sulfentrazone and thiencarbazone-methyl were detected in the negative mode (ESI-). All compounds were successfully separated in less than 3.0 min. Further optimization achieved desired recoveries ranging from 74.5 to 102.1% for all analytes with relative standard deviation values ≤17.2% in all tested matrices at three levels (10, 100, and 500 μg/kg). The limits of detection for all compounds were ≤2.3 μg/kg, and the limits of quantitation did not exceed 7.1 μg/kg. The developed method showed excellent linearity (R(2) ≥ 0.994) and was proven to be highly efficient and reliable for the routine monitoring of triazolone herbicides in cereals.