Navegando por Autor "Neves, Antônio A."
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Item Análise de resíduos de agrotóxicos em tomates empregando dispersão da matriz em fase sólida (DMFS) e cromatografia gasosa(Química Nova, 2009) Pinho, Gevany P.; Neves, Antônio A.; Queiroz, Maria Eliana L. R.This work was aimed on optimization of the matrix solid-phase dispersion (MSPD) technique using gas chromatography for analyzing residues of chlorpyriphos, λ-cyhalothrin, cypermethrin and deltamethrin in tomatoes. The results showed that silica was more efficient for the clean up of extracts, but florisil provided the highest recovery rates. A 23 complete factorial design was carried out to evaluate the absorbent/sample ratio, presence of co-column (silica) and ultrasonic bath on the extraction rate. The percentage of extraction of the pesticides chlorpyriphos, λ-cyhalothrin, cypermethrin and deltamethrin were 64.7, 88.3, 99.2 and 89.2%, respectively, with relative standard deviations below 5%.Item Aqueous ozone solutions for pesticide removal from potatoes(Food Science and Technology International, 2016-04-28) Heleno, Fernanda F.; Queiroz, Maria Eliana L.R. de; Faroni, Lêda R.A.; Neves, Antônio A.; Oliveira, André F. de; Costa, Luiz P.L.; Pimenta, Gustavo G.The presence of pesticide residues in potatoes is of concern because of the potential impact to human health due to the high consumption of this vegetable. In this study, aqueous solutions with and without ozone saturation as postharvest wash treatment at pH 4.0, 7.0, and 9.0 were tested to remove chlorothalonil from potatoes. The method used for pesticide analysis has been validated, presenting recovery values of 94–103%, with variations in the repeatability coefficients of 10.6%, and a quantification limit of 0.05 mg kg 1 . Regardless of pH, treatment with aqueous ozone solutions removed 70–76% of the pesticide present in the potato. In the no-ozone treatments, the percentage average removal of chlorothalonil residues in potatoes was only 36%. Over 24 days of storage, the quality of potatoes washed with aqueous ozone solutions was not significantly different from those washed with pure water.Item Determinação simultânea de trialometanos e agrotóxicos em água por cromatografia gasosa(Química Nova, 2010-11-30) Carlos, Elenice A.; Neves, Antônio A.; Reis, César; Queiroz, Maria Eliana L. R. deA method for simultaneous analysis of trihalomethanes and organochloride and pyrethroid pesticides in water utilizing SPME-HS and GC-ECD was developed. In the optimized method 25 mL of water containing 2% (w/v) Na2HPO4 were heated to 60 °C for 50 min. The fiber (PDMS - 100 μm) was exposed to a headspace for the same period. For all analytes it was found that LOQ < MCL (Maximum Contaminant Level), CV < 20% and r > 0.9. The method was applied to potable and surface water samples. Some trihalomethanes were encountered in potable waters, at levels below the MCL.Item Determination of pesticides in lettuce using solid–liquid extraction with low temperature partitioning(Food Chemistry, 2015-02-20) Costa, Anna I.G.; Queiroz, Maria E.L.R.; Neves, Antônio A.; Sousa, Flaviane A. de; Zambolim, LaércioThis work describes the optimization and validation of a method employing solid–liquid extraction with low temperature partitioning (SLE/LTP) together with analysis by gas chromatography with electron capture detection (GC/ECD) for the determination of nine pesticides (chlorothalonil, methyl parathion, procymidone, endosulfan, iprodione, λ-cyhalothrin, permethrin, cypermethrin, and deltamethrin) in lettuce. The method was found to be selective, accurate, and precise, with means recovery values in the range of 72.3–103.2%, coefficients of variation ⩽12%, and detection limits in the range 0.4–37 μg kg−1. The matrix components significantly influence the chromatographic response of the analytes (above 10%). The optimized and validated method was applied to determine the residual concentrations of the fungicides iprodione and procymidone that had been applied to field crops of lettuce. The maximum residual concentrations of the pesticides in the lettuce samples were 13.6 ± 0.4 mg kg−1 (iprodione) and 1.00 ± 0.01 mg kg−1 (procymidone), on the day after application of the products.Item DLLME-GC/ECD Method for the Residual Analysis of Parathion-Methyl and its Application in the Study of the UV-Photodegradation Process(Journal of the Brazilian Chemical Society, 2017-11) Pimenta, Gustavo G.; Queiroz, Maria E. L. R. de; Victor, Raquel P. D.; Noronha, Luiz M.; Neves, Antônio A.; Oliveira, André F. de; Heleno, Fernanda F.A new method has been developed to determine trace levels of organophosphorus pesticide parathion-methyl in water samples by using dispersive liquid-liquid microextraction (DLLME), followed by gas chromatograph coupled with electron capture detector (GC/ECD) analysis. The optimized and validated method showed high extraction recovery (101.1%), high enrichment factor (57.3), low limits of detection and quantification, 0.083 and 0.250 µg L-1, respectively. The established DLLME-GC/ECD method has been successfully applied for the evaluation of the photodegradation of the parathion-methyl by UV254nm radiation in different conditions of pH and temperature. The parathion-methyl photodegradation at pH 3 and 35 °C achieved > 99.5% after 120 min of exposition. For this condition, it was observed the kinetic rate of 0.0515 min-1, the quantum yield of 1.22 × 10-5 mol Einstein-1 and a half-life time of 13.46 min. All experimental conditions tested proved to be strongly influenced by pH and temperature. The application of the optimized process in distilled and drinking water spiked with parathion-methyl provided residues of this pesticide at levels below the maximum permitted by Brazilian legislation, which is 9.0 µg L-1.Item Headspace solid phase microextraction-gas chromatography for the determination of trihalomethanes in fish(Microchemical Journal, 2017-07) Delvaux Júnior, Nelson A.; Queiroz, Maria E.L.R. de; Neves, Antônio A.; Oliveira, André F.; Silva, Marcos R. F. da; Faroni, Lêda R. A.; Heleno, Fernanda F.The aim of this work is to develop a method for determining trihalomethanes (THMs) in fish samples. The proposed method uses solid phase microextraction and gas chromatography with an electron capture detector. Factors such as temperature, extraction time and type of fiber were assessed to maximize the performance of the extraction technique. The performance of the method was evaluated using selectivity, linearity, precision, accuracy and limits of detection (LOD) and quantification (LOQ). The new method allows analysis of THMs with appropriate selectivity and linearity, with coefficient of correlation > 0.98. The LOD and LOQ of the analytes of interest are from 0.11 to 0.35 μg kg− 1 and 0.35 to 1.18 μg kg− 1, respectively. In addition, the relative standard deviation (RSD) was between 1.6 and 8%, and the relative recovery was between 76 and 113%. The optimized and validated method was applied to fish samples purchased from the Viçosa (MG) local market. At least three of the THMs of interest were detected in most of the analyzed fish samples with maximum values for the concentration of chloroform, bromodichloromethane and bromoform at 8.33, 0.42 and 2.41 μg kg− 1, respectively.Item Impact of percentage and particle size of sugarcane biochar on the sorption behavior of clomazone in Red Latosol(Anais da Academia Brasileira de Ciências, 2018-10) Silva, Marcos R. F. da; Queiroz, Maria Eliana L. R. de; Neves, Antônio A.; Silva, Antônio A. da; Oliveira, André F. de; Oliveira, Renan L. de; Azevedo, Mariane M.Biochar is a carbonaceous material that has excellent potential as a fertilizer and soil conditioner. However, there is a lack of information concerning the effects of the amount and particle size of this pyrogenic material on the soil sorption capacity. In this work, evaluation was made of changes in clomazone (CMZ) sorption in a Red Latosol following soil conditioning using different percentages (0.25, 0.5, and 1% w/w) of sugarcane biochar in three particle sizes (<106, 106-508, and 508-610 μm). The conditioned soils presented apparent sorption coefficients (Kd) up to 1300 times higher than that of pure soil, besides changes in the behavior of CMZ sorption. The biochar particle size and percentage influenced sorption of the herbicide as well as its retention in the amended soil during desorption processes. Both sorption and desorption Freundlich constants were linearly correlated with the external surface area of the biochar present in the soil.Item Mobility and persistence of the herbicide fomesafen in soils cultivated with bean plants using SLE/LTP and HPLC/DAD(Environmental Science and Pollution Research, 2014-09-23) Costa, Anna I. G.; Queiroz, Maria Eliana L. R.; Neves, Antônio A.; Assis, Roberta C. de; Soares, Carlos E. S. dos; Silva, Antônio A. da; D’Antonino, Leonardo; Oliveira, André F. de; Bellato, Carlos R.A method has been optimized and validated for the determination of fomesafen in soils using solid–liquid extraction with low-temperature partitioning (SLE/LTP) and analysis by liquid chromatography with a high-efficiency diode array detector (HPLC/DAD). The method was used to evaluate the persistence and mobility of this herbicide in different soils cultivated with bean plants. Recovery values were ≥98.9 %, with variations in the repeatability coefficients of ≤15 %, and a detection limit of 7.3 μg kg−1. Half-life values of fomesafen were between 60 and 71 days in soil cultivated using a no-till system and 99 and 114 days in soil cultivated using a conventional tillage system. The mobility of fomesafen was moderate and mainly influenced by the organic matter content, pH, and soil type. In Red-Yellow Argisol, which has a higher content of organic matter, the leaching of fomesafen was less pronounced. In Red-Yellow Latosol, which has smaller amounts of organic matter and high pH, the leaching of fomesafen was more pronounced.Item A new spectrophotometric method for determination of EDTA in water using its complex with Mn(III)(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2016-06-06) Andrade, Carlos Eduardo O.; Oliveira, André F.; Neves, Antônio A.; Queiroz, Maria Eliana L.R.EDTA is an important ligand used in many industrial products as well as in agriculture, where it is employed to assist in phytoextraction procedures and the absorption of nutrients by plants. Due to its intensive use and recalcitrance, it is now considered an emerging pollutant in water, so there is great interest in techniques suitable for its monitoring. This work proposes a method based on formation of the Mn(III)-EDTA complex after oxidation of the Mn(II)-EDTA complex by PbO2 immobilized on cyanoacrylate spheres. A design of experiments (DOE) based on the Doehlert matrix was used to determine the optimum conditions of the method, and the influence of the variables was evaluated using a multiple linear regression (MLR) model. The optimized method presented a linear response in the range from 0.77 to 100.0 μmol L− 1, with analytical sensitivity of 7.7 × 103 L mol− 1, a coefficient of determination of 0.999, and a limit of detection of 0.23 μmol L− 1. The method was applied using samples fortified at different concentration levels, and the recoveries achieved were between 97.0 and 104.9%.