Fengshou Dong

Simultaneous determination of four neonicotinoid insecticides residues in cereals, vegetables and fruits using ultra-performance liquid chromatography/tandem mass spectrometry

A rapid multi-residue analytical method was developed for the determination of four nicotinoid insecticides (thiacloprid, thiamethoxam, clothianidin, and dinotefuran) in cereals, vegetables and fruits using QuEChERS method and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were extracted by acetonitrile and subsequently cleaned up using primary secondary amine (PSA) and graphitized carbon black (GCB) prior to UPLC-MS/MS analysis. The determination of the target compounds was achieved in less than 2.5 min using an electrospray ionization source in positive ion mode (ESI+). The method showed good linearity in the concentration range of 0.01–1 mg L−1 with correlation coefficients >0.999. Recovery studies were performed at three fortification levels of 0.01, 0.05, and 0.5 mg kg−1 in blank rice, wheat, cucumber, tomato, cabbage, apple, and peach samples. The overall average recoveries ranged from 82.7% to 103.4% with intra-day relative standard deviations (RSDr) which ranged between 1.3% and 7.9% and inter-day RSD (RSDR) from 3.9% to 11.6%, respectively. The limits of detection (LOD) were below 0.68 μg kg−1, while the limits of quantification (LOQ) were 0.71–2.26 μg kg−1. The developed analytical method provides a basis for monitoring neonicotinoid insecticide residues in cereals, vegetables and fruits.

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.

Determination of sulfoxaflor residues in vegetables, fruits and soil using ultra-performance liquid chromatography/tandem mass spectrometry

Sulfoxaflor is a novel sulfoximine insecticide which is effective against a wide range of sap-feeding insect pests, including aphids, whiteflies, hoppers, and lygus. In this study, a rapid, highly sensitive and selective method was developed for determining sulfoxaflor residues in vegetables, fruits and soil by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The target compound was extracted with acetonitrile and cleaned with dispersive solid phase extraction using primary and secondary amine (PSA). Two pairs of precursor product ion transitions for sulfoxaflor were measured and evaluated. Satisfactory linearities in the range of 10–1000 μg L−1 of sulfoxaflor were obtained, where the correlation coefficients (R2) were higher than 0.9977 in all cases. Average recoveries in cucumber, tomato, cabbage, apple, grape and soil at three levels (10 μg kg−1, 100 μg kg−1 and 1000 μg kg−1) ranged from 78.4% to 98.7%, with relative standard deviations (RSDr) from 1.2% to 14.5%. The reproducibility (RSDR) ranged from 2.9 to 15.6%. The LODs ranged from 0.2 to 0.6 μg kg−1, and LOQs from 0.7 to 2.0 μg kg−1. This method was used to determine sulfoxaflor residues in cucumber and soil samples for studies of their dissipation under field conditions. The trial results showed that the half-lives of sulfoxaflor obtained after treatment ranged from 1.6 to 2.9 days in cucumber and from 1.5 to 7.2 days in soil in Shandong, Henan and Zhejiang. The developed analytical method provides a basis to establish maximum residue limits and monitor sulfoxaflor residues in vegetables and fruits.

Simultaneous determination of three strobilurin fungicide residues in fruits, vegetables and soil by a modified quick, easy, cheap, effective, rugged (QuEChERS) method coupled with gas chromatography-tandem mass spectrometry

A gas chromatography-tandem mass spectrometry (GC-MS/MS) method followed by a modified quick, easy, cheap, effective, rugged (QuEChERS) method for the analysis of three strobilurin fungicide residues (picoxystrobin, kresoxim-methyl and trifloxystrobin) in fruits, vegetables and soil was developed and validated. The three fungicides were extracted with ethyl acetate and cyclohexane (v/v = 1/1), and subsequently cleaned up using a combination of primary secondary amine and graphitized carbon black prior to GC-MS/MS analysis. The three fungicides were qualitatively determined using the multiple reaction monitoring mode with two ion transitions measured for each fungicide and evaluation by collision tests, and were determined quantitatively using the external standard method. Recovery studies were performed at three fortification levels of 0.005, 0.05, and 0.5 mg kg−1 in blank cucumber, tomato, apple, grape and soil samples. The overall average recoveries ranged from 87% to 112%, with intra-day relative standard deviations (RSDs) of 0.9% to 10.5% and inter-day RSD of 0.7% to 12.2%, respectively. The calculated limits of detection and quantification were typically below 0.006 and 0.019 μg kg−1 for GC-MS/MS. The results of the method validation confirm that this proposed method is easy and reliable for the determination of residues of strobilurin fungicides in fruits, vegetables and soil.

Effect of tetraconazole application on the soil microbial community.

Tetraconazole is one of the most commonly used triazole fungicides in agricultural practice, and its continuous application poses a potential risk for non-target soil microorganisms. Therefore, the objective of this study was to evaluate the effect of tetraconazole at the field rate (T1, 0.33xa0mgkg−1 of soil), three times the field rate (T3, 1.00xa0mgkg−1 of soil) and 10 times the field rate (T10, 3.33xa0mgkg−1 of soil) on the soil microorganisms. To ascertain this effect, the tetraconazole concentration and the microbial properties with potential as bioindicators of soil health (i.e. microbial biomass C, basal respiration, substrate-induced respiration, structure diversity and functional community profiling) were determined. The results showed that the degradation half-lives of tetraconazole varied from 69 to 87xa0days, depending on the three application concentrations. The microbial biomass C, basal respiration and substrate-induced respiration were inhibited, but they tended to recover at the end of the incubation when tetraconazole was applied at the recommended field rate. The ratios of the gram-negative to gram-positive (GN to GP) bacteria decreased, and the fungi to bacteria ratio increased after a temporal decrease on the seventh day. A principal component analysis of the PLFAs showed that tetraconazole application significantly shifted the microbial community structure on day 7. Different functional community profiles were observed, depending on the tetraconazole application rates. It was concluded that tetraconazole application decreases the soil microbial biomass and activity and changes the structures of the soil microbial community.

Rapid residue analysis of pyriproxyfen, avermectins and diflubenzuron in mushrooms by ultra-performance liquid chromatography coupled with tandem mass spectrometry

A quick, easy, cheap, effective, rugged, and safe (QuEChERS) analytical procedure for the simultaneous determination of pyriproxyfen, diflubenzuron and avermectin residues in mushrooms and their substrates was developed using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Pyriproxyfen, diflubenzuron and avermectin were extracted with acetonitrile and the purification procedure was carried out using primary-secondary amine (PSA). The determination of target compounds was achieved in less than 3.0 min using an electrospray ionization source in positive mode (ESI+). Chromatographic separation was achieved using gradient elution with a mobile phase consisting of acetonitrile and water containing 0.2% formic acid. Average recoveries were in the range of 78.1–112.5% with the relative standard deviation values below 11.8% for all analytes. The limits of detection ranged from 0.016 to 1.5 μg kg−1, and limits of quantification ranged from 0.052 to 5 μg kg−1. The results of the method validation confirmed that this proposed method is convenient and reliable for the determination of pyriproxyfen, diflubenzuron and avermectin residues in mushrooms and their substrates.

Determination of flumetsulam residues in 20 kinds of plant-derived foods by ultra-performance liquid chromatography coupled with tandem mass spectrometry

A modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method for the simultaneous quantitative determination of flumetsulam in 20 kinds of complicated plant-derived food grains (rice, wheat, and corn), vegetables (cabbage, celery, tomato, kidney bean, eggplant, potato, radish and leek), fruits (apple, peach, grape and orange), edible mushroom (mushroom), tea (green tea), nuts (almond), oil crops (soybean) and edible oil (peanut oil) was developed and validated using ultra-performance LC coupled with MS/MS. Acetonitrile was the extraction solvent and simultaneous liquid–liquid partitioning was formed by adding anhydrous magnesium sulfate (MgSO4) and sodium chloride (NaCl). The extract was then cleaned up by dispersive-SPE using graphitized carbon black (GCB), almond and peanut oil using Cleanert Florisil, as selective sorbents. The determination of the target compound was achieved in less than 6.0 min using an electrospray ionization source in positive mode (ESI+). Quantification was performed by calibration curves of standards from 0.01–1.0 mg L−1 with r2 = 0.999. Further optimization of sample preparation and determination achieved recoveries between 73.85% and 115.76% for all analytes with RSD values lower than 10% in 20 kinds of plant-derived foods at three levels (10, 50 and 100 μg kg−1).

Determination of phthalanilic acid residue in bean, fruits and vegetables using a modified QuEChERS method and ultra-performance liquid chromatography/tandem mass spectrometry

A rapid, sensitive and selective method for determining phthalanilic acid residue in bean, fruits and vegetables based on a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction procedure was developed by ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). The samples were extracted by acidified acetonitrile (0.4% (v/v) formic acid) and simultaneous liquid–liquid partitioning formed by adding anhydrous magnesium sulfate (MgSO4) and sodium chloride (NaCl). The extract was then cleaned up by dispersive-SPE using florisil and graphitized carbon black (GCB) as selective sorbent. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. The method showed good linearity in the concentration range of 10–1000 μg L−1, with correlation coefficients ≥0.997. Recovery studies were performed at three fortification levels of 10, 100 and 1000 μg kg−1 in soybean, apple, grape, cucumber, tomato and pepper. Further optimization of sample preparation and determination achieved recoveries ranging between 70.1% and 105.3% for the analyte with 0.7–14.9% intra-day relative standard deviations (RSD) and 0.2–8% inter-day RSD at three spiked levels (10, 100 and 1000 μg kg−1). The limits of detection (LOD) were below 1 μg kg−1, and the limits of quantification (LOQ) did not exceed 3 μg kg−1. The effects of two columns on the separation were also investigated. The method is demonstrated to be convenient and reliable for determination of phthalanilic acid in bean, fruits and vegetables. With the developed method, 60 samples of commercial fruit products (grape, apple), soybean and vegetables (pepper, tomato, cucumber) were analyzed. Phthalanilic acid was not detected in all samples.

Stereoselective separation and determination of the triazole fungicide propiconazole in water, soil and grape by normal phase HPLC

An effective normal phase HPLC method was developed and validated for stereoselective determination of propiconazole enantiomers in water, soil and grape. The performances of five different chiral stationary phases were evaluated for the separation of propiconazole enantiomers. And the effects of organic alcohols in the mobile-phase and column temperature on the enantioseparation were also investigated. Baseline separation of propiconazole enantiomers was successfully obtained on an OD-H column with n-hexane–ethanol (95u2006:u20065, v/v) as the mobile phase at a flow rate of 0.6 mL min−1 with UV detection at 220 nm and temperature at 25 °C. Based on this enantioseparation method, enantioselective analysis methods for this fungicide in water, soil and grape matrices were developed and validated. Parameters including linearity, precision, accuracy, limits of detection (LOD) and limits of quantification (LOQ) were investigated. The mean recoveries from three matrices were satisfactory, ranging from 89.6% to 99.8%, with relative standard deviations in the range of 1.6–9.5% at three fortification levels. LOD for the four stereoisomers in water, soil and grape were less than 0.02 mg kg−1, whereas LOQ did not exceed 0.05 mg kg−1. The methodology was also successfully applied for the enantioselective analysis of real samples, confirming the application of this method.

Simultaneous determination of hexanoic acid 2-(diethylamino)ethyl ester and mepiquat chloride by ultra-performance liquid chromatography coupled to tandem mass spectrometry

A rapid and sensitive method for simultaneous determination of hexanoic acid 2-(diethylamino)ethyl ester (DA-6) and mepiquat chloride (MQ) residues in soil and cotton samples was developed using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). DA-6 and MQ were extracted with water–0.6% formic acid containing 5.0 mL 0.2% NH4Cl (cotton seeds 2% NH4Cl). Then, extracts containing the target compounds were analysed using UPLC-MS/MS with an electrospray ionization source in positive mode. The determination of the target compounds was achieved in less than 2.0 min. The limits of detection (LOD) were below 0.005 mg kg−1, while the limits of quantification (LOQ) did not exceed 0.015 mg kg−1 in all three matrices. Quantification was performed by calibration curves of standards from 0.005–1.0 mg kg−1 with r2 > 0.997. Recovery studies were evaluated at three spiked levels 0.5, 1.0 and 2.0 mg kg−1 for soil and cotton samples, and the overall average recoveries ranged from 76.3% to 100.0% with relative standard deviations 4.7–11.8% (n = 5).