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Search Results: 1 - 10 of 185455 matches for " Ivanildo Luiz de Mattos "
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Detection of Total Phenol in Green and Black Teas by Flow Injection System and Unmodified Screen Printed Electrode
Ivanildo Luiz de Mattos,José Heraclito Zagal
International Journal of Analytical Chemistry , 2010, DOI: 10.1155/2010/143714
Abstract: A flow injection system using an unmodified gold screen-printed electrode was employed for total phenol determination in black and green teas. In order to avoid passivation of the electrode surface due to the redox reaction, preoxidation of the sample was realized by hexacyanoferrate(III) followed by addition of an EDTA solution. The complex formed in the presence of EDTA minimizes or avoids polymerization of the oxidized phenols. The previously filtered tea sample and hexacyanoferrate(III) reagent were introduced simultaneously into two-carrier streams producing two reproducible zones. At confluence point, the pre-oxidation of the phenolic compounds occurs while this zone flows through the coiled reactor and receives the EDTA solution before phenol detection. The consumption of ferricyanide was monitorized at 360?mV versus Ag/AgCl and reflected the total amount of phenolic compounds present in the sample. Results were reported as gallic acid equivalents (GAEs). The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35–40 samples per hour with detection limit = 1?mg/L without the necessity for surface cleaning after each measurement. Precise results are in agreement with those obtained by the Folin-Ciocalteu method. 1. Introduction Phenolic compounds are a class of chemicals that have a hydroxyl functional group attached to an aromatic hydrocarbon group. The simplest of the class is phenol (C6H5OH) [1]. The term “polyphenols” refers to a group of chemical substances found in plants which are characterized by the presence of more than one phenol unit, for example, hydrolysable tannins (gallic acid) and phenylpropanoids (flavonoid, lignins, and condensed tannins) [1, 2]. The largest and most studied polyphenols are the flavonoids, as catechins, which correspond to the main phenolic compound found in green and black teas [3]. Gallic acid was identified to be main free phenolic acids; the four major catechins are (?)-epicatechin gallate (ECG), (?)-epigallocatechin (EGC), (?)-epigallocatechin gallate (EGCG), and (?)-epicatechin (EC). These species can be associated to a reduction in the risk of cardiovascular disease and some forms of cancer, as well as the improvement of oral health and other physiological functions such as anti-hypertensive effect, body weight control, antibacterial and antivirasic activity, and so forth [1–4]. Therefore, the development of analytical methods for polyphenols represents an important and exciting topic for analytical
Filmes de metal-hexacianoferrato: uma ferramenta em química analítica
Mattos, Ivanildo Luiz de;Gorton, Lo;
Química Nova , 2001, DOI: 10.1590/S0100-40422001000200010
Abstract: chemically modified electrodes based on hexacyanometalate films are presented as a tool in analytical chemistry. use of amperometric sensors and/or biosensors based on the metal-hexacyanoferrate films is a tendency. this article reviews some applications of these films for analytical determination of both inorganic (e.g. as3+, s2o32-) and organic (e.g. cysteine, hydrazine, ascorbic acid, gluthatione, glucose, etc.) compounds.
Filmes de metal-hexacianoferrato: uma ferramenta em química analítica
Mattos Ivanildo Luiz de,Gorton Lo
Química Nova , 2001,
Abstract: Chemically modified electrodes based on hexacyanometalate films are presented as a tool in analytical chemistry. Use of amperometric sensors and/or biosensors based on the metal-hexacyanoferrate films is a tendency. This article reviews some applications of these films for analytical determination of both inorganic (e.g. As3+, S2O3(2-)) and organic (e.g. cysteine, hydrazine, ascorbic acid, gluthatione, glucose, etc.) compounds.
A FAST, ROBUST ELECTROCHEMICAL METHOD FOR THE AUTOMATED DETERMINATION OF HYDROGEN PEROXIDE
MATTOS,IVANILDO LUIZ DE; CAROLI,MARCOS; AREIAS,MADALENA; NAVARRO,MARCELO;
Journal of the Chilean Chemical Society , 2009, DOI: 10.4067/S0717-97072009000400020
Abstract: a suitable fow-injection method for the analysis of commercial solutions of hydrogen peroxide is described. a nafon-coated glassy carbon electrode, modifed by deposition of copper hexacyanoferrate (cuchf), is employed as an amperometric sensor. the method allows the analysis of 45 samples per hour, with peroxide concentrations in the range of 1.25 -10.0 mm, with relative standard deviations smaller than 1%.
Pervapora??o: uma técnica de separa??o contínua n?o-cromatográfica
Mattos, Ivanildo Luiz de;Queiroz, Rold?o R. U.;
Química Nova , 1998, DOI: 10.1590/S0100-40421998000200016
Abstract: a brief discussion of the non-chromatographic continuous separation techniques is presented emphasizing the pervaporation process. it makes interesting choices for implementing various preliminary operations of the analytical process in order to accommodate the raw sample to the measuring instrument. discussions include the perceived advantages and disadvantages, the underlying principles of pervaporation process, the flexible module and fields of application.
Pervapora o: uma técnica de separa o contínua n o-cromatográfica
Mattos Ivanildo Luiz de,Queiroz Rold?o R. U.
Química Nova , 1998,
Abstract: A brief discussion of the non-chromatographic continuous separation techniques is presented emphasizing the pervaporation process. It makes interesting choices for implementing various preliminary operations of the analytical process in order to accommodate the raw sample to the measuring instrument. Discussions include the perceived advantages and disadvantages, the underlying principles of pervaporation process, the flexible module and fields of application.
A FAST, ROBUST ELECTROCHEMICAL METHOD FOR THE AUTOMATED DETERMINATION OF HYDROGEN PEROXIDE
IVANILDO LUIZ DE MATTOS,MARCOS CAROLI,MADALENA AREIAS,MARCELO NAVARRO
Journal of the Chilean Chemical Society , 2009,
Abstract: A suitable fow-injection method for the analysis of commercial solutions of hydrogen peroxide is described. A Nafon-coated glassy carbon electrode, modifed by deposition of copper hexacyanoferrate (CuCHF), is employed as an amperometric sensor. The method allows the analysis of 45 samples per hour, with peroxide concentrations in the range of 1.25 -10.0 mM, with relative standard deviations smaller than 1%.
Peróxido de hidrogênio: importancia e determina??o
Mattos, Ivanildo Luiz de;Shiraishi, Karina Antonelli;Braz, Alexandre Delphini;Fernandes, Jo?o Roberto;
Química Nova , 2003, DOI: 10.1590/S0100-40422003000300015
Abstract: a brief discussion about the hydrogen peroxide importance and its determination is presented. it was emphasized some consideration of the h2o2 as reagent (separated or combined), uses and methods of analysis (techniques, detection limits, linear response intervals, sensor specifications). moreover, it was presented several applications, such as in environmental, pharmaceutical, medicine and food samples.
Determina??o indireta de N-total em plantas por espectrometria de absor??o at?mica com chama empregando uma mini-coluna de AgCl(s)
Carneiro, Josiane Meire Tolotti;Zagatto, Elias Ayres Guidetti;Mattos, Ivanildo Luiz de;Melo, Denise;
Scientia Agricola , 2001, DOI: 10.1590/S0103-90162001000100023
Abstract: a flow-injection system with a agcl(s) mini-column is proposed for the determination of total nitrogen in plant digests by flame atomic absorption spectrometry. the method is based on ag+ removal by ammonia through the formation of the diammine argentate(i) complex and further monitoring of the released ag+. nitrogen was determined in seven reference samples, in three replicates, with precision and accuracy comparable to the conductimetric procedure. the system is robust, and only slight sensitivity variations (< 2 %) have been noted during extended (4 h) operating periods. sampling rate is about 100 h-1 and measurement repeatability is fair (relative standard deviation usually < 0.02).
Peróxido de hidrogênio: importancia e determina o
Mattos Ivanildo Luiz de,Shiraishi Karina Antonelli,Braz Alexandre Delphini,Fernandes Jo?o Roberto
Química Nova , 2003,
Abstract: A brief discussion about the hydrogen peroxide importance and its determination is presented. It was emphasized some consideration of the H2O2 as reagent (separated or combined), uses and methods of analysis (techniques, detection limits, linear response intervals, sensor specifications). Moreover, it was presented several applications, such as in environmental, pharmaceutical, medicine and food samples.
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