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35 results on '"dos Santos, Vagner Bezerra"'

11. A novel approach to Hg2+ determination in water samples using carbon dots based on paper and fluorescence digital image analysis.

Author

Maia, Matheus Valentin, Suarez, Willian Toito, dos Santos, Vagner Bezerra, de Oliveira, Severino Carlos Bezerra, and de Almeida, João Paulo Barbosa

Subjects
DIGITAL images, ELECTRONIC paper, IMAGE analysis, WATER sampling, SUSTAINABLE chemistry, WATER use, QUANTUM dots, MERCURY
Abstract

BACKGROUND: This work proposes the use of a simple, inexpensive method for the hydrothermal synthesis of fluorescent carbon dot nanoparticles (CDs) from rice starch aimed at the determination of Hg2+ in water. The proposed method involved using a paper‐based analytical device coupled to a 3D plate, with a UV‐LED chamber and a smartphone for the acquisition and analysis of the fluorescence digital images of the CDs. RESULTS: The size of the carbon dots ranged from 0.5 to 3 nm, with an average particle size of ~1 nm. The functionalization of carbon dots with methimazole allowed a high selective for Hg2+ determination. The results obtained showed a linear response R2 of 0.997 and Hg2+ concentration in the range of 0.5–45.0 μmol L−1 with a limit of detection and limit of quantitation of 0.23 and 0.62 μmol L−1, respectively. The results of the study show that there were no significant differences, at 95% confidence level, between the data obtained from the application of the proposed method and the reference method. CONCLUSION: The proposed method is in line with the principles of green chemistry, as it involves the use of renewable sources for starch extraction and a hydrothermal synthesis process that does not employ toxic reagents. In addition, the method employs only 15 μL reagent/sample. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Published
2024
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20. Digital image-based flame emission spectrometry

Author

Silva Lyra, Wellington, dos Santos, Vagner Bezerra, Dionízio, Amália Geiza Gama, Martins, Valdomiro Lacerda, Almeida, Luciano Farias, Nóbrega Gaião, Edvaldo, Diniz, Paulo Henrique Gonçalves Dias, Silva, Edvan Cirino, and Araújo, Mário César Ugulino

Published
2009
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23. DEVELOPMENT AND VALIDATION OF ANALYTICAL METHODOLOGY BASED ON DIGITAL IMAGES OF SPOT TEST FOR DETERMINATION OF ETHANOL IN CACHAÇA

Author

Pessoa, Kenia Dias, Suarez, Willian Toito, Lopes, Renata Pereira, dos Reis, Marina Ferreira, Franco, Mathews de Oliveira Krambeck, and dos Santos, Vagner Bezerra

Subjects
RGB, determination, DETERMINAÇÃO, lcsh:T, ETANOL, lcsh:Q, ethanol, cachaça, lcsh:Science, lcsh:Technology, CACHAÇA
Abstract

In this work it is carried out the development, optimization and validation of analytical methodology for determination of ethanol in cachaça samples. The method was based on digital image analysis spot test performed with the analyte of interest, captured by a camera in a system built for this purpose. The principle of the method is measurement of tones obtained after the occurrence of the colorimetric reaction employing the RGB color model, color components which varies in proportion to the analyte concentration. For the determination of ethanol, it was employed the reaction of redox in which chromium (VI) is reduced to chromium (III) or chromium (II) and the ethanol is oxidized to acetaldehyde, generating change in the yellow-orange color to blue-green. By determining the ethanol content, a linear calibration curve in the range from 10 to 70% v/v ethanol was obtained, with a coefficient of determination r2 = 0.9910 and limits of detection and quantification respectively equal to 1.72 % v/v and 5.74% v/v. Comparison of results for the cachaça samples analysis using the developed method and the reference method showed no significant differences between both methods, which were analyzed using the paired t-test, 95% confidence. The analysis of six cachaça samples showed that three of them had ethanol content outside the range permitted by law. Besides the image capture system is versatile and robust and can be used in situ analysis. A análise de imagens digitais é um método analítico baseado na decomposição da imagem, cujos os valores RGB variam proporcionalmente com a concentração do analito. Para a determinação de etanol, empregou-se a reação de óxido-redução na qual o cromo (VI) é reduzido a cromo (III) ou cromo (II), sendo o etanol oxidado a aldeído acético, gerando mudança da cor amarelo-alaranjada para verde-azulada. Foi obtida uma curva analítica linear no intervalo de 10 a 70 % v/v de etanol, com coeficiente de regressão r2 = 0,991. Os limites de detecção e de quantificação foram iguais à 1,72 % v/v e 5,74 % v/v. Seis amostras de cachaça foram analisadas empregando o método proposto e um método picnométrico, e conclui-se que três delas apresentaram teor de etanol fora da faixa permitida pela legislação. O método analítico baseado em imagens digitais mostrou-se versátil, preciso, exato, de custo baixo e com baixa geração de resíduos, muito útil para análises in situ.

Published
2017

24. Determination of theobromine and caffeine in fermented and unfermented Amazonian cocoa (Theobroma cacao L.) beans using square wave voltammetry after chromatographic separation

Author

Júnior, Paulo Cardoso Gomes, primary, dos Santos, Vagner Bezerra, additional, Lopes, Alessandra Santos, additional, de Souza, José Pio Iúdice, additional, Pina, Jeferson Rodrigo Souza, additional, Chagas Júnior, Gilson Celso Albuquerque, additional, and Marinho, Patrícia Santana Barbosa, additional

Published
2020
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34. Nitroprusside as a Novel Reagent for Flow Injection Spectrophotometric Determination of Captopril.

Author

de Oliveira, Denílson Mendes, Suarez, Willian Toito, Júnior, Benedito Roberto Alvarenga, Gabriel, Wesley Lira, and dos Santos, Vagner Bezerra

Subjects
SODIUM nitroferricyanide, CHEMICAL reagents, FLOW injection analysis, SPECTROPHOTOMETRY, CAPTOPRIL
Abstract

A novel flow injection system for the determination of captopril in pharmaceutical formulations is described. Nitroprusside was employed as a new, nontoxic reagent. Captopril reacted with nitroprusside in basic solution to yield a red chromophore with maximum absorbance at 521 nm. The calibration relationship was linear for concentrations from 3.0 × 10−6to 1.0 × 10−3 mol L−1with a limit of detection of 1.0 × 10−6 mol L−1. The recoveries from captopril tablets were between 99.7 and 102.3%. The sampling frequency was 50 h−1and the relative standard deviation was estimated to be 1.0% for 5.0 × 10−4 mol L−1captopril. A pairedt-test showed that analysis of tablets by the flow procedure and a potentiometry provided similar results at the 95% confidence level. [ABSTRACT FROM PUBLISHER]

Published
2016
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35. A Compact Microcontrolled Microfluidic System for Photometric Determination of Phosphate in Natural Water Samples.

Author

Pessoa-Neto, Osmundo Dantas, Silva, Tiago Almeida, dos Santos, Vagner Bezerra, and Fatibello-Filho, Orlando

Abstract

A compact environmentally friendly microcontrolled microfluidic device ideal for in situ phosphate determination was developed based on a microsystem based on low-temperature co-fired ceramics (LTCC) coupled to a light-emitting diode (LED)-photometer with a multicommutation flow analysis (MCFA) approach. The experimental parameters of the MCFA analyzer were optimized by chemometric studies. Under the best experimental conditions, limits of detection and quantification of 0.02mg PL[sup -1] and 0.07mg PL[sup -1], respectively, and a sampling frequency of 67h[sup -1] were estimated. Moreover, a low sample consumption of only 60µL per determination was the other advantage that fully meets the requirements of sustainable research and green chemistry purposes. [ABSTRACT FROM AUTHOR]

Published
2015
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