Method validation, residue analysis and dietary risk assessment of trifloxystrobin and trifloxystrobin acid in milk, eggs and pork.

Trifloxystrobin (TFS) is a widely used strobilurin fungicide and its residues accumulating in animal-derived food could result in potential harm to consumers. By optimization of extraction solvents and cleanup sorbents, a residue analysis method for TFS and its metabolite trifloxystrobin acid (TFSA) was established in milk, eggs and pork based on QuEChERS sample preparation and LC-MS/MS. The calibration curves exhibited good linearity with determination coefficients (R2 ) >0.9930 over the range of 0.5-250 ng/ml for both TFS and TFSA. The recoveries of the two analytes were 81-100% with RSD 3-10% and 76-96% with RSD 2-13%, respectively. The limit of quantification (LOQ) was 1 ng/g for both analytes. The milk, egg and pork samples, 30 each, were collected from the 30 main producing regions in China, and residues of TFS and TFSA were analyzed. The concentrations of both analytes were lower than the corresponding LOQs and maximum residue limits. Long-term dietary risk assessment showed that the hazard quotients were 0.001-0.003%, indicating an absence of unacceptable risks in milk, eggs and pork to the health of common consumers in China.

Residue Behavior and Risk Assessment of Pyraclostrobin and Thifluzamide in Cowpea.

A rapid and sensitive analytical method for determination of pyraclostrobin and thifluzamide in cowpea was established based on QuEChERS sample preparation and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Average recoveries of pyraclostrobin and thifluzamide on cowpea were 100%-105% and 99%-105% with RSDs of 1%-5% and 2%-6%, respectively. The storage stability tests showed degradation rates of < 20% for samples stored at - 18℃ within 12 weeks. The field trials at eight locations in China showed that the residues of pyraclostrobin in cowpea at 3 and 5 days after spraying were 0.081-0.49 mg/kg and 0.029-0.48 mg/kg, and the residues of thifluzamide were 0.12-0.46 mg/kg and 0.047-0.50 mg/kg, respectively, which were all lower than the corresponding maximum residue limits in China. The dissipation of both pyraclostrobin and thifluzamide in cowpea were fast with half-lives (T1/2) of 1.5-2.3 days and 1.7-2.4 days. This study provided risk assessment data for establishment of good agricultural practice in cowpea plant.

Method validation and residue analysis of methoxyfenozide and metaflumizone in Chinese broccoli under field conditions by liquid chromatography with tandem mass spectrometry.

Methoxyfenozide and metaflumizone are insecticides used on Chinese broccoli to prevent insects and increase yield. However, the residues are potentially harmful to the environment and consumers. In this study, the quick, easy, cheap, effective, rugged, safe method with high-performance liquid chromatography with tandem mass spectrometry was modified and validated for determination of methoxyfenozide and metaflumizone in Chinese broccoli. The clean-up efficiency of different sorbents including C18 , primary secondary amine, graphitized carbon black, and carbon nanofiber was compared. Recoveries of the validated method were 71.8-94.6% with relative standard deviations of 1.5-3.2% and the limits of quantification were 0.01 and 0.005 mg/kg for methoxyfenozide and metaflumizone, respectively. A storage stability test showed almost no degradation of methoxyfenozide in Chinese broccoli, however, the degradation rate of metaflumizone was 22.9% after 10-wk storage at -20°C. In field trials in four producing regions, the dissipation of both methoxyfenozide and metaflumizone in Chinese broccoli was fast, with half-lives of only 1.0-5.1 and 0.7-2.5 days, respectively. Terminal residues after application of the two pesticides were all below 1.0 mg/kg after 5 days.

Hydrolysis Kinetics of a Novel 3,4-Dichloroisothiazole Plant-Activator Candidate LY5-24-2 by UPLC-Q-TOF.

Hydrolysis characteristics of a novel 3,4-dichloroisothiazole based fungicide with activating plant defense responses as a candidate plant-activator LY5-24-2 were investigated under different conditions (pH and temperature) using ultra-performance liquid chromatography (UPLC) and quadrupole Time-of-Flight (Q-TOF). The hydrolysis case complied with the first-order kinetic model, with half-lives ranging from 4.8 h to 3.2 days at pH 4, 7, 9 and temperature at 25 and 50℃. One of the hydrolysis metabolite 3,4-dichloroisothiazole-5-carboxylic acid (metabolite 1, M1) was determined and quantified using authentic standard. The other hydrolysate 3-chloro-5-(trifluoromethyl) pyridin-2-amine (metabolite 2, M2) was determined and identified according to accurate mass information, fragmentation patterns and principle component analysis (PCA). By utilizing high-resolution mass spectrometry and multivariate statistical analysis, hydrolysis dynamic of the metabolites was characterized and figured out. This research provided a non-target screening method to analyze hydrolysis metabolites of a new plant-activator and to find its degradation products in aqueous solution.

Comparison of pulse glow discharge-ion mobility spectrometry and liquid chromatography with tandem mass spectrometry based on multiplug filtration cleanup for the analysis of tricaine mesylate residues in fish and water.

Analytical methods based on multiplug filtration cleanup coupled with pulse glow discharge-ion mobility spectrometry and liquid chromatography tandem mass spectrometry were developed for the analysis of tricaine mesylate residue in fish and fish-raising water samples. A silica fiber holder and an appropriate new interface were designed to make the direct introduction of the fiber into the pulse glow discharge-ion mobility spectrometry introduction mechanism. The multiplug filtration cleanup method with adsorption mixtures was optimized for the determination of tricaine mesylate in fish samples. Good linear relationships were obtained by the two methods. For fish samples, limits of detection were 6 and 0.6 µg/kg by ion mobility spectrometry and liquid chromatography with tandem mass spectrometry, respectively. The matrix effect of the established liquid chromatography tandem mass spectrometry method was negligible for fish samples but that of the ion mobility spectrometry method was not. The two methods were compared. The ion mobility spectrometry system could be used a rapid screening tool on site with the advantage of rapidity, simplicity, and portability, and the liquid chromatography tandem mass spectrometry system could be used for validation in laboratory conditions with the advantage of lower limit of detection, stability, and precision.

Method validation, storage stability and field trial for residues of florasulam and pyroxsulam in cereal by liquid chromatography with tandem mass spectrometry.

A QuEChERS method with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was modified and validated for the determination of florasulam and pyroxsulam residues in wheat grain and straw. The validated method was applied to cereals including oat, millet, corn and rice. Average recoveries were 76-113% with RSDs 2-15%. The limits of quantitation (LOQ) were 0.005 mg/kg for wheat grain and 0.01 mg/kg for wheat straw and four cereals. Ion suppression for florasulam (-28% to -76%) was observed in all the matrices except corn, whereas ion enhancement were shown for pyroxsulam (44% to 83%). Degradation rates of florasulam and pyroxsulam were 6% and 23%, respectively, in wheat grain and straw after eight-week storage at -20°C. The ultimate residues in field trials in ten regions were all ≤0.05 mg/kg, and long term dietary risk assessment indicated that hazard quotients were 0.02% and 0.001% for florasulam and pyroxsulam, respectively, which shows that it is safe to spray the two herbicides on wheat.

Evaluation of cleanup procedures in pesticide multi-residue analysis with QuEChERS in cinnamon bark.

Cinnamon bark is a very complex spices matrix for pesticide residue analysis. In this study, two cleanup procedures, dispersive solid-phase extraction (d-SPE) and repetitive d-SPE, combined with Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction were both investigated and applied for the determination of 60 pesticide residues in cinnamon bark by liquid chromatography - tandem mass spectrometry (LC-MS/MS) detection. The extraction solvents, phase partition salts, and cleanup sorbents were optimized. The results showed that 150 mg MgSO4 + 50 mg C18 showed the best performance in d-SPE. The repetitive d-SPE achieved less matrix effects than d-SPE, but several high water-solubility analytes were lost during the cleanup, and also the 10 fold dilution compromised the sensitivities of analytes. With the validated QuEChERS-d-SPE method, 44 of 60 pesticides obtained satisfactory recoveries (71%-118%) and RSDs (2%-27%) at three to five spiking levels. The method was applied to monitor 15 market cinnamon samples.

Residue Analysis of 60 Pesticides in Red Swamp Crayfish Using QuEChERS with High-Performance Liquid Chromatography-Tandem Mass Spectrometry.

In this study, a multi-residue analytical method using quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and dispersive solid-phase extraction (d-SPE) cleanup, followed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), was investigated for rapid determination of 60 pesticide residues in whole crayfish and crayfish meat. The final method used 10 mL of acetonitrile for extraction, 3 g of NaCl for partitioning, and 50 mg of primary secondary amine for d-SPE cleanup. The method was validated at three spiking levels (10, 50, and 100 ng/g) using triphenyl phosphate as an internal standard and both gradient and isocratic HPLC elution. Under gradient conditions, satisfactory recoveries (70-120%) and relative standard deviations of ≤20% were achieved for 83 and 88% of pesticides in whole crayfish and crayfish meat, respectively. Matrix effects were estimated using both gradient and isocratic HPLC elution. To our knowledge, this is the first study involving multi-residue analysis of HPLC-amenable pesticides in crayfish and mantis shrimp. The final method was successfully applied for analysis of 11 crayfish and mantis shrimp samples from markets in China, and propamocarb (

The comparison of dispersive solid phase extraction and multi-plug filtration cleanup method based on multi-walled carbon nanotubes for pesticides multi-residue analysis by liquid chromatography tandem mass spectrometry.

In this study, dispersive-Solid Phase Extraction (d-SPE) cleanup and multi-plug filtration cleanup (m-PFC) methods were compared for 25 representative pesticides in six matrices (wheat, spinach, carrot, apple, citrus and peanut) by QuEChERS-LC-ESI-MS/MS detection. The type of sorbents in dispersive-SPE (d-SPE) was optimized for the above matrices. Multi-walled carbon nanotubes (MWCNTs), which mixed other materials like PSA (Primary Secondary Amines), GCB (Graphitized Carbon Black) and C18 (Octadecyl-silica), showed brilliant cleanup performance in multi residue monitoring (MRM) pesticide residue analysis. Cleanup effects with d-SPE and m-PFC methods were examined. When spiked at 3 concentration levels of 10, 100, 500 µg/kg in above matrices, for both d-SPE and m-PFC methods, the recoveries ranged from 70 to 110% with relative standard deviations (RSDs) lower than 20%. Limits of quantification (LOQs) for both cleanup methods ranged from 1 to 25 µg/kg. Matrix-matched calibrations were performed with the coefficients of determination more than 0.99 between concentration levels of 10-1000 µg/kg. It was found that m-PFC was more convenient and effective than d-SPE with the same sorbents, due to the increased contact time and contact area between the extracts and compressed sorbents. The study demonstrated that m-PFC method could be used as a rapid, convenient and high-throughput cleanup method for analysis of pesticide residues.