A method was developed using matrix solid-phase dispersion, together with liquid chromatography with ultraviolet diode array detector for determination of carbofuran, difenoconazole, β-cyfluthrin, spirodiclofen and thiophanate-methyl in stem of coconut palm. The best results were obtained using 2.0 g of stem, 1.6 g of Florisil as sorbent and cyclohexane:acetone mixture (4:1). The method was validated using stem samples spiked with pesticides at four concentration levels (0.05-2.0 μg/g). Average recoveries ranged from 70 % to 114.3 %, with relative standard deviations between 1.2 % and 19.2 %. Detection and quantification limits were in the ranges 0.02-0.03 and 0.05-0.1 μg/g, respectively.
Background: Pesticides are applied for pest control during the production of cereal grains used in beer production. Given the risks for consumers, it is important to analyze the pesticide residues. Objective: Quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based methods are very effective, and improvement inthe cleanup step is an important approach. Methods: Primary secondary amine (PSA) andmagnesium silicate were evaluated for dispersive-solid-phase extraction (d-SPE) cleanup step in extracts provided by the QuEChERS method in combination with GC-tandem MS for the determination of acetamiprid, terburfos, alachlor, ametryn, atrazine, azoxystrobin, carbofuran, carbosulfan, cypermethrin, deltamethrin, difenoconazole, esfenvalerate, flutriafol,thiamethoxam, and parathion-methyl in lager beer. Results: The amount of 50 mg of magnesium silicate was suitable for cleaning up beer extract as an alternative d-SPE material to PSA. Themethod was validated using beer fortified with pesticides at three concentration levels (0.002, 0.01, and 0.1 μg/mL). Average recoveries ranged from 70 to 123%, with RSDs between 0.3 and 10.5 %. Matrix effects were observed by comparing the slope of matrix-matched standard calibration with that of solvent. The method provided good linearity at the concentration levels of 0.001–2.5 μg/mL. Detection limits ranged from 0.0001 to 0.0007 μg/mL and quantification limits ranged from 0.001 to 0.006 μg/mL. The method was applied to nine beer brands. Conclusions: Results showed that magnesium silicate is an efficient alternative cleanup material to reduce analysiscosts while maintaining the method reliability and accuracy. Highlights: Magnesium silicate was effective as adsorbent for d-SPE step inthe analysis of pesticides in beer.
An extraction method based on solid-phase extraction was developed to determine the major alkaloid components, N,N-dimethyltryptamine, harmine, harmaline, harmalol, and tetrahydroharmine, in ayahuasca using ultra-performance liquid chromatography-tandem mass spectrometry. Coconut charcoal and menthone-thiosemicarbazone polymer were tested as new adsorbent materials. Experiments carried out at levels of 1, 5, 10, 50, 100, and 250 μg mL-1 resulted in recoveries in the ranges 45.3-115.7% for menthone-thiosemicarbazone and 40.6-116.2% for coconut charcoal. The detection and quantification limits ranged from 0.003 to 0.016 μg mL-1 and from 0.009 to 0.043 μg mL-1 , respectively. The method developed was linear over the tested range (0.05-1.0 μg mL-1), with correlation coefficients ranging from 0.9969 to 0.9998. The technique was applied for analysis of the compounds in an ayahuasca sample collected from a religious group located in the city of Fortaleza, obtaining concentrations in the range from 0.3 to 19.3 mg mL-1 .
A new nanocomposite based on ZnCdTe semiconductor nanocrystals (NCs) synthesized in situ on reduced graphene oxide (rGO) was obtained. The heterostructure was characterized using UV-Vis emission and absorption spectroscopies, which provided evidences of the growth of the nanocrystals onto the rGO matrix. To evaluate the electrochemical performance, carbon paste electrodes modified with the nanocomposite (QD-rGO/CPE) were prepared, showing high sensitivity in the electroanalytical detection of the pesticide carbendazim. Under optimal operational conditions a calibration curve was constructed with a linear behavior in the range of 9.98 × 10 -8 to 1.18 × 10 -5 mol L -1 , with a correlation coefficient of 0.997. The limit of detection (LOD) and the limit of quantification (LOQ) for carbendazim were 9.16 × 10 -8 and 2.78 × 10 -7 mol L -1 , respectively. The electrode is successfully applied for the determination of carbendazim in orange juice samples.
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