Effects of light shading and climatic conditions on the metabolic behavior of flonicamid in red bell pepper.

The degradation behavior of flonicamid and its metabolites (4-trifluoromethylnicotinic acid (TFNA) and N-(4-trifluoromethylnicotinoyl) glycine (TFNG)) was evaluated in red bell pepper over a period of 90 days under glass house conditions, including high temperature, low and high humidity, and in a vinyl house covered with high density polyethylene light shade covering film (35 and 75%). Flonicamid (10% active ingredient) was applied (via foliar application) to all fruits, including those groups grown under normal conditions (glass house) or under no shade cover (vinyl house). Samples were extracted using a Quick, Easy, Cheap, Effective, Rugged, and Safe "QuEChERS" method and analyzed using liquid chromatography-tandem mass spectrometry (LC/MS/MS). The method performance, including linearity, recovery, limits of detection (LOD), and quantitation (LOQ), was satisfactory. Throughout the experimental period, the residual levels of flonicamid and TFNG were not uniform, whereas that of TFNA remained constant. The total sum of the residues (flonicamid and its metabolites) was higher in the vinyl house with shade cover than in the glass house, under various conditions. The total residues were significantly higher when the treatment was applied under high light shade (75%). The flonicamid half-life decreased from 47.2 days (under normal conditions) to 28.4 days (at high temperatures) in the glass house, while it increased from 47.9 days (no shade cover) to 66 days (75% light shading) in the vinyl house. High humidity leads to decreases in the total sum of flonicamid residues in red bell pepper grown in a glass house, because it leads to an increase in the rate of water loss, which in turn accelerates the volatilization of the pesticide. For safety reasons, it is advisable to grow red bell pepper under glass house conditions because of the effects of solar radiation, which increases the rate of flonicamid degradation into its metabolites.

Analysis of mandipropamid residual levels through systematic method optimization against the matrix complexity of sesame leaves using HPLC/UVD.

An analytical method was developed to detect mandipropamid residues in sesame leaves using high-performance liquid chromatography-ultraviolet detection. Samples were extracted with acetonitrile and were prepurified using a solid-phase extraction (SPE) cartridge with an additional dispersive-SPE (d-SPE) sorbent application. The method was validated using an external calibration curve prepared using pure solvent. The linearity was excellent with determination coefficient = 1. The limits of detection and quantification were 0.003 and 0.01 mg/kg, respectively. Recoveries at three spiking levels - 0.1, 0.5, and 1.0 mg/kg - were in the range 80.3-90.7% with relative standard deviations <2%. This method was applied to field-treated samples collected from two different areas, Gwangju and Muan, in the Republic of Korea and the half-lives were similar, 5.10 and 5.41 days, respectively. The pre-harvest residue limit was also predicted for both sites. The proposed method is sensitive and able to quantify trace amounts of mandipropamid in leafy vegetables. The combination of SPE and d-SPE effectively removed the matrix components in sesame leaves. Copyright © 2015 John Wiley & Sons, Ltd.

Simultaneous detection of fluquinconazole and flusilazole in lettuce using gas chromatography with a nitrogen phosphorus detector: decline patterns at two different locations.

Method validations in addition to decline patterns of fluquinconazole and flusilazole in lettuce grown under greenhouse conditions at two different locations were investigated. Following the application of fluquinconazole and flusilazole at a dose rate of 20 mL/20 L water, lettuce samples were collected randomly for up to 7 days post-application, and simultaneously extracted with acetone, purified through solid-phase extraction, analyzed via gas chromatography with a nitrogen phosphorus detector, and confirmed through gas chromatography-mass spectrometry. The linearity was excellent, with determination coefficients (R(2) ) between 0.9999 and 1.0. The method was validated in triplicate at two different spiking levels (0.2 and 1.0 mg/kg) with satisfactory recoveries between 75.7 and 97.9% and relative standard deviations of <9. The limit of quantification was 0.01 mg/kg. Both analytes declined very quickly, as can be seen from the short half-life time of <4 days. Statistical analysis revealed significant differences between residues at different days of sampling, except at 7 days post-application (triple application). At that point, the decline patterns of fluquinconazole and flusilazole were independent of application rate, location, temperature and humidity. Copyright © 2015 John Wiley & Sons, Ltd.

A combination of solid-phase extraction and dispersive solid-phase extraction effectively reduces the matrix interference in liquid chromatography-ultraviolet detection during pyraclostrobin analysis in perilla leaves.

Perilla leaves contain many interfering substances; thus, it is difficult to protect the analytes during identification and integration. Furthermore, increasing the amount of sample to lower the detection limit worsens the situation. To overcome this problem, we established a new method using a combination of solid-phase extraction and dispersive solid-phase extraction to analyze pyraclostrobin in perilla leaves by liquid chromatography with ultraviolet absorbance detection. The target compound was quantitated by external calibration with a good determination coefficient (R(2) = 0.997). The method was validated (in triplicate) with three fortification levels, and 79.06- 89.10% of the target compound was recovered with a relative standard deviation <4. The limits of detection and quantification were 0.0033 and 0.01 mg/kg, respectively. The method was successfully applied to field samples collected from two different areas at Gwangju and Muan. The decline in the resiudue concentrations was best ascribed to a first-order kinetic model with half-lives of 5.7 and 4.6 days. The variation between the patterns was attributed to humidity.

Dynamic behaviour and residual pattern of thiamethoxam and its metabolite clothianidin in Swiss chard using liquid chromatography-tandem mass spectrometry.

A simultaneous method was developed to analyse thiamethoxam and its metabolite clothianidin in Swiss chard using tandem mass spectrometry (in the positive electrospray ionisation mode using multiple reaction monitoring mode) to estimate the dissipation pattern and the pre-harvest residue limit (PHRL). Thiamethoxam (10%, WG) was sprayed on Swiss chard grown in two different areas under greenhouse conditions at the recommended dose rate of 10 g/20 L water. Samples were collected randomly up to 14 days post-application, extracted using quick, easy, cheap, effective, rugged, safe (QuEChERS) acetate-buffered method and purified via a dispersive solid phase extraction (d-SPE) procedure. Matrix matched calibration showed good linearity with determination coefficients (R(2)) ⩾ 0.998. The limits of detection (LOD) and quantification (LOQ) were 0.007 and 0.02 mg/kg. The method was validated in triplicate at two different spiked concentration levels. Good recoveries (n=3) of 87.48-105.61% with relative standard deviations (RSDs) < 10 were obtained for both analytes. The rate of disappearance of total thiamethoxam residues in/on Swiss chard was best described by first-order kinetics with half-lives of 6.3 and 4.2 days. We predicted from the PHRL curves that if the residues were <19.21 or 26.98 mg/kg at 10 days before harvest, then total thiamethoxam concentrations would be below the maximum residue limits during harvest.