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Dive into the research topics where Maria Eliana Lopes Ribeiro de Queiroz is active.

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Featured researches published by Maria Eliana Lopes Ribeiro de Queiroz.


Talanta | 2008

Low-temperature clean-up method for the determination of pyrethroids in milk using gas chromatography with electron capture detection

Simone Machado Goulart; Maria Eliana Lopes Ribeiro de Queiroz; Antônio Augusto Neves; José Humberto de Queiroz

This paper describes a new gas-chromatography with electron capture detection (GC-ECD) method for determination of some pyrethroids in milk samples. The extraction of the pyrethroids was carried out by liquid-liquid extraction with clean-up by precipitation at low temperature, without additional stages for removal of fat interferences. The method was efficient with recoveries of 93.0+/-0.1% for cipermethrin and 84.0+/-0.3% for deltamethrin. The quantification limits were 0.75 microg L(-1) for both pyrethroids. The method was simple, of easy execution, and used only small quantities of organic solvent. After optimization and validation, the method was used for the determination of residues of the pyrethroids cipermethrin and deltamethrin in milk and in lactea drink commercialized in Viçosa (MG, Brazil). Some samples presented contamination with deltamethrin at levels below the maximum contamination limits established by the FAO.


Analytica Chimica Acta | 2010

Optimization and validation of liquid–liquid extraction with low temperature partitioning for determination of carbamates in water

Simone Machado Goulart; Renata Domingos Alves; Antônio Augusto Neves; José Humberto de Queiroz; Tamires Condé de Assis; Maria Eliana Lopes Ribeiro de Queiroz

Using a 2(3) experimental design, liquid-liquid extraction with low temperature partitioning (LLE-LTP) was optimized and validated for analysis of three carbamates (aldicarb, carbofuran and carbaryl) in water samples. In this method, 2.0 mL of sample is placed in contact with 4.0 mL of acetonitrile. After agitation, the sample is placed in a freezer for 3 h for phase separation. The organic extract is analyzed by high performance liquid chromatography with ultraviolet detection (HPLC-UV). For validation of the technique, the following figures of merit were evaluated: accuracy, precision, detection and quantification limits, linearity, sensibility and selectivity. Extraction recovery percentages of the carbamates aldicarb, carbofuran and carbaryl were 90%, 95% and 96%, respectively. Even though extremely low volumes of sample and solvent were used, the extraction method was selective and the detection and quantification limits were between 5.0 and 10.0 microg L(-1), and 17.0 and 33.0 microg L(-1), respectively.


Química Nova | 2007

Otimização e validação da técnica de extração líquido-líquido com partição em baixa temperatura (ELL-PBT) para piretróides em água e análise por CG

Heulla Pereira Vieira; Antônio Augusto Neves; Maria Eliana Lopes Ribeiro de Queiroz

The liquid-liquid extraction with the low temperature partition technique was developed for the analysis of four pyrethroids in water by CG. Using a factorial design the extraction technique was optimised evaluating the effect of the variables ionic strength, contact time and proportion between sample and solvent volumes. The validation parameters sensitivity, precision, accuracy and detection and quantification limits were evaluated. The LOD and LOQ of the method varied from 1.1 to 3.2 µg L-1 and 2.7 to 9.5 µg L-1, respectively.


Química Nova | 2009

Efeito de matriz na quantificação de agrotóxicos por cromatografia gasosa

Gevany Paulino de Pinho; Antônio Augusto Neves; Maria Eliana Lopes Ribeiro de Queiroz; Flaviano Oliveira Silvério

The lack of accuracy of a chromatographic method can be associated with the matrix effect. This effect is observed in pesticide quantification by gas chromatography when the chromatographic signals of standards prepared in solvents are compared with those of the analyte in extracts of complex matrices. In the competition between the matrix components and the pesticides for the active sites of the liner, a larger amount of pesticides is transferred to the column, giving apparent extractions above 100%. In this work, we discuss factors that contribute to the matrix effect and present some attempts to overcome the problem.


Talanta | 2012

Determination of maleic hydrazide residues in garlic bulbs by HPLC

Claudia Mamani Moreno; Teodoro Stadler; Antonio Alberto da Silva; Luiz C. A. Barbosa; Maria Eliana Lopes Ribeiro de Queiroz

In recent years, the release of information about the preventative and curative properties of garlic on different diseases and their benefits to human health has led to an increase in the consumption of garlic. To meet the requirements of international markets and reach competitiveness and profitability, farmers seek to extend the offer period of fresh garlic by increasing post-harvest life. As a result, the use of maleic hydrazide (1,2-dihydropyridazine-3,6-dione) [MH], a plant growth regulator, has been widespread in various garlic growing regions of the world. The present work was undertaken to develop and validate a new analytical procedure based on MH extraction from garlic previously frozen by liquid nitrogen and submitted to low temperature clean-up. The applicability of the method by analysis of garlic samples from a commercial plantation was also demonstrated. The influence of certain factors on the performance of the analytical methodology were studied and optimized. The approach is an efficient extraction, clean-up and determination alternative for MH residue-quantification due to its specificity and sensitivity. The use of liquid nitrogen during the sample preparation prevents the degradation of the analyte due to oxidation reactions, a major limiting factor. Moreover, the method provides good linearity (r(2): 0.999), good intermediate precision (coefficient of variation (CV): 8.39%), and extracts were not affected by the matrix effect. Under optimized conditions, the limit of detection (LOD) (0.33 mg kg(-1)) was well below the maximum residue level (MRL) set internationally for garlic (15 mg kg(-1)), with excellent rates of recovery (over 95%), good repeatability and acceptable accuracy (CV averaged 5.74%), since garlic is a complex matrix. The analytical performance of the methodology presented was compared with other techniques already reported, with highly satisfactory results, lower LOD and higher recoveries rates. In addition, the extraction process is simple, not expensive, easily executable and requires lower volumes of organic solvent. The proposed methodology removes the need of extensive typical laboratory extraction procedures, reducing the amount of time needed for pesticide analysis and increasing sample throughput. Adopting this method gives food safety laboratories the potential to increase cost savings by a suitable technique in routine testing to determine MH residues in garlic.


International Journal of Environmental Analytical Chemistry | 2007

Determination of disulfoton in surface water samples by cloud-point extraction and gas chromatography

Anizio M. Faria; Raquel P. Dardengo; Claudio F. Lima; Antônio Augusto Neves; Maria Eliana Lopes Ribeiro de Queiroz

This article proposes an alternative method, using cloud-point extraction and gas chromatography, for extraction and determination of disulfoton in water samples. For cloud-point extraction, the nonionic surfactant Triton X-114 was used. Before gas chromatography, a cleanup stage for surfactant removal from the extracts was optimized. Cleanup used two columns, in series, containing silica gel and Florisil, with methanol:hexane (1 : 1) as eluent, resulting in the removal of more than 95% of the Triton X-114. Factors such as ionic strength (>0.5 mol L−1) and surfactant concentration (1.0% w/v) increased the extraction efficiency of the cloud-point methodology, yielding disulfoton recoveries of almost 100%. Compared with liquid–liquid extraction, the cloud-point methodology was more efficient, with a better detectability, and resulted in a significant reduction in solvent volume.


Journal of Environmental Science and Health Part B-pesticides Food Contaminants and Agricultural Wastes | 2014

Effects of ozone fumigation treatment on the removal of residual difenoconazole from strawberries and on their quality

Fernanda Fernandes Heleno; Maria Eliana Lopes Ribeiro de Queiroz; Antônio Augusto Neves; Romenique da Silva de Freitas; Lêda R. A. Faroni; André F. Oliveira

The effect of ozone fumigation on the reduction of difenoconazole residue on strawberries was studied. Strawberries were immersed in 1.0 L of aqueous solution containing 400 μL of the commercial product (250 g L−1 of difenoconazole) for 1 min. Then, they were dried and exposed to ozone gas (O3) at concentrations of 0.3, 0.6 and 0.8 mg L−1 for 1 h. The ozone fumigation treatments reduced the difenoconazole residue on strawberries to concentrations below 0.5 mg kg−1, which corresponds to a 95% reduction. The strawberries treated with ozone and the control group, which was not treated with ozone, were stored at 4°C for 10 days. Some characteristics of the fruit were monitored throughout this period. Among these, pH, weight loss and total color difference did not change significantly (P > 0.05). The fumigation with ozone significantly affected the soluble solids, titratable acidity and ascorbic acid content (vitamin C) of the strawberries preventing a sharp reduction of these parameters during storage.


Food Chemistry | 2015

Determination of pesticides in lettuce using solid-liquid extraction with low temperature partitioning.

Anna I. G. Costa; Maria Eliana Lopes Ribeiro de Queiroz; Antônio Augusto Neves; Flaviane A. de Sousa; Laércio Zambolim

This 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.


Journal of the Brazilian Chemical Society | 2013

Determination of chlorpyrifos and thiamethoxam in potato tuber (Solanum tuberosum L.) and soil of Brazil using solid-liquid extraction with low temperature partitioning (SLE/LTP)

Leila M. B. Rigueira; Kamilla de L. Ribeiro; Maria Eliana Lopes Ribeiro de Queiroz; Antônio Augusto Neves; Laércio Zambolim; Ricardo M. Oliveira

The main objective of this work was to evaluate the presence of residues of chlorpyrifos and thiamethoxam in potato and soil samples under different circumstances after optimization and validation of solid-liquid extraction and partitioning at low temperature technique. Recovery percentages between 93% and 105% were obtained for pesticides in the samples. The optimized and validated method was applied to potatoes from supermarkets and it was obtained chlorpyrifos residue at concentrations of 0.67 mg kg-1. Potatoes grown in the field were treated with pesticide on different days and chlorpyrifos was the only residue detected. The potatoes grown in pots were treated with chlorpyrifos and thiamethoxam only at planting. After 91 days, it was observed the concentration of thiamethoxam in the potatoes higher than the tolerable MRL. The proposed method was efficient in the determination of chlorpyrifos and thiamethoxam and it was concluded that the monitoring of pesticides in food must be performed periodically to ensure the product quality and the safety of consumers health.


Journal of Environmental Science and Health Part B-pesticides Food Contaminants and Agricultural Wastes | 2013

Sorption and desorption of sulfentrazone in Brazilian soils

Ana Beatriz R. J. Passos; M.A.M. Freitas; Lívia G. Torres; Antonio Alberto da Silva; Maria Eliana Lopes Ribeiro de Queiroz; Claudio F. Lima

This study was undertaken to obtain information about the behavior of sulfentrazone in soil by evaluating the sorption and desorption of the herbicide in different Brazilian soils. Batch equilibrium method was used and the samples were analyzed by high performance liquid chromatography. Based on the results obtained from the values of Freundlich constants (Kf), we determined the order of sorption (Haplic Planosol < Red-Yellow Latosol < Red Argisol < Humic Cambisol < Regolitic Neosol) and desorption (Regolitic Neosol < Red Argisol < Humic Cambisol < Haplic Planosol < Red-Yellow Latosol) of sulfentrazone in the soils. The process of pesticide sorption in soils was dependent on the levels of organic matter and clay, while desorption was influenced by the organic matter content and soil pH. Thus, the use of sulfentrazone in soils with low clay content and organic matter (low sorption) increases the probability of contaminating future crops.

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Antônio Augusto Neves

Universidade Federal de Viçosa

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André F. Oliveira

Universidade Federal de Viçosa

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Gevany Paulino de Pinho

Universidade Federal de Viçosa

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Antonio Alberto da Silva

Universidade Federal de Viçosa

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Flaviano Oliveira Silvério

Universidade Federal de Minas Gerais

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Anna I. G. Costa

Universidade Federal de Viçosa

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Tanus Jorge Nagem

Universidade Federal de Ouro Preto

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Flaviane A. de Sousa

Universidade Federal de Viçosa

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