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Adsorptive Stripping Voltammetric Determination of Hydroquinone using an Electrochemically Pretreated  Glassy Carbon Electrode

Adsorptive Stripping Voltammetric Determination of Hydroquinone using an Electrochemically Pretreated Glassy Carbon Electrode

A simple and efficient adsorptive stripping voltammetric (AdSV) method was developed for the determination of hydroquinone at an electrochemically pretreated glassy carbon (GC) electrode in waste water. Various parameters such as solvent system, accumulation potential, accumulation time and scan rate were optimized. The electrochemically pretreated GC electrode showed good response towards hydroquinone determination by using AdSV. Under the optimized conditions the peak current showed good linear relationship with the hydroquinone concentration in the range of 0.5-4.0mg L -1 and 5-30mg L -1 . The 60/40 methanol/water composition was found to be the best solvent system and 0.05mol L -1 H 2 SO 4 was found as useful supporting electrolyte concentration.
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Voltammetric characteristics of miconazole and its cathodic stripping voltammetric determination

Voltammetric characteristics of miconazole and its cathodic stripping voltammetric determination

Apparatus: Voltammetric experiments were per- formed with a Metrohm Polarecord E 506 linked to a compatible microcomputer, through a Microquim- ica interface. The multimode electrode Metrohm stand 663 VA was used in both the hanging mercury electrode (HMDE) and dropping mercury electrode (DME). The three electrode system was completed means of an Ag/AgCl (3 mol L −1 KCl) reference electrode and a glassy carbon auxiliary electrode. Reagents: Suprapur grade reagents supplied by Merck and desmineralized water from a Milli-Q sys- tem (Milli-pore) were used in the preparation of all solutions. Britton-Robinson (B-R) buffer used as supporting electrolyte was prepared by mixing ap- propriate amounts of 0.2 mol L -1 sodium hydroxide to orthophosphoric acid, acetic acid and boric acid (0.04 mol L -1 in each) solution.
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Electrochemical reduction and cathodic stripping voltammetric determination of clotrimazole

Electrochemical reduction and cathodic stripping voltammetric determination of clotrimazole

Voltammetric experiments were performed with a Metrohm Polarecord E 506 linked to a compatible microcomputer, through a Microquimica interface. The multimode electrode Metrohm stand 663 VA was used in both the hanging mercury drop electrode (HMDE) and dropping mercury electrode (DME). The three electrode system was completed by means of an Ag/AgCl (3 mol L -1 KCl) reference electrode and a glassy

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Anodic stripping voltammetric determination of copper (II) in wastewaters using a carbon paste electrode modified with chitosan.

Anodic stripping voltammetric determination of copper (II) in wastewaters using a carbon paste electrode modified with chitosan.

Finalmente, utilizando voltametria de redissolução anódica em um intervalo de potencial de –0,2 a 0,5 V, a uma velo- cidade de varredura de potencial de 25 mV s -1 , ocorre a oxidação de[r]

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J. Braz. Chem. Soc.  vol.22 número2

J. Braz. Chem. Soc. vol.22 número2

of the C=N group of the acidic and basic forms of irbesartan, respectively. A validated square-wave adsorptive cathodic stripping voltammetric method was developed for quantiication of irbesartan in the bulk form. The developed stripping voltammetric method was successfully applied for quantitation of irbesartan in pharmaceutical formulations and spiked human serum, without the necessity for samples pretreatment and/or time-consuming extraction steps prior to the analysis. Insigniicant interferences from its active ingredient “hydrochlorothiazide”, excipients, common metal ions and co-administrated drugs were obtained during the analysis. Limits of detection of 9.0x10 -10 and 2.1x10 -9 mol L -1 and limits of quantitation of 3.0x10 -9 and 7.0x10 -9 mol L -1 irbesartan
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J. Braz. Chem. Soc.  vol.22 número11

J. Braz. Chem. Soc. vol.22 número11

As flavonoids show pharmacological activity, in the present investigation, an economical and efficient method for their trace determination was developed. In this context, the interfacial behavior of three flavonoids, 3-hydroxyflavone (3HF), morin and hesperidin (Hesp) was studied on the hanging mercury dropping electrode (HMDE) by phase sensitive ac voltammetry and cyclic voltammetry (CV). The investigated flavonoids were strongly adsorbed which is the prerequisite step for applying the cathodic adsorption stripping voltammetric determination of some flavonoids. Based on the adsorption character of investigated flavonoids onto the surface of the HMDE, validated, simple, fast and sensitive square-wave cathodic adsorptive stripping voltammetric (SWCASV) procedure for the quantification of the flavonoids under investigation in bulk form and in biological fluids was described. Moreover, controlled adsorptive accumulation of the Cu(II) complex of flavonoids was also achieved to assay indirect determination of 3HF, morin and Hesp via the reduction of the formed complex. Operational and solution conditions for the quantitative ultra-trace determination of the investigated flavonoids were optimized in the absence and presence of Cu(II). Limits of detection of 4.4 × 10 -9 , 7.19 × 10 -9 and 7.54 × 10 -9 mol L -1 3HF, morin and
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Quantitative determination of glycyrrhizinic acid by square-wave

Quantitative determination of glycyrrhizinic acid by square-wave

In the family of pulse techniques square-wave voltamme- try appears to be one of the most advanced electroanalytical techniques (17). This technique is attributed with unique advantages, such as: high frequency and amplitude, solitary approach in the current-sampling procedure, as well as the effective ability to discriminate the capacity current. Thus, for developing a particular absorptive stripping voltammetric method for determination of miscellaneous species, square- wave voltammetry is most frequently a technique of choice.

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J. Braz. Chem. Soc.  vol.20 número10

J. Braz. Chem. Soc. vol.20 número10

Validation of the described stripping voltammetric method for assay of bulk gatiloxacin was examined via evaluation of the linear dynamic range, limit of detection (LOD), limit of quantitation (LOQ), repeatability, reproducibility, precision, robustness and intermediate precision. Linear calibration plots over various concentration ranges of bulk gatiloxacin, at various accumulation durations were obtained and the characteristics of these plots are reported in Table 1. Values of LOD and LOQ were estimated using the expression: k S.D./ b, 48 where k = 3 for LOD and 10 for LOQ, S.D. is
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J. Braz. Chem. Soc.  vol.22 número9

J. Braz. Chem. Soc. vol.22 número9

work reports a new stripping voltammetric procedure for trace detection of efavirenz based on its adsorption at a thin-ilm mercury electrode. The advantages, instrumental parameters and possible limitations of this procedure are also explained in this work. Furthermore, the effects of a wide range of potentially interfering compounds, such as the antiviral drugs didanosine, acyclovir, nevirapine, indinavir, nelinavir, saquinavir, lamivudine, zidovudine, some metal ions and ATP or DNA were examined.

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UNIVERSIDADE FEDERAL DE UBERLÂNDIA INSTITUTO DE QUÍMICA PROGRAMA DE PÓS-GRADUAÇÃO EM QUÍMICA

UNIVERSIDADE FEDERAL DE UBERLÂNDIA INSTITUTO DE QUÍMICA PROGRAMA DE PÓS-GRADUAÇÃO EM QUÍMICA

Nesta tese foi demonstrado que a associação da técnica eletroanalítica Voltametria de Redissolução Anódica de Onda Quadrada (SWASV, do inglês, Square-Wave Anodic Stripping Voltammetry[r]

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Aplicação de processos físico-químicos como alternativa de pré e pós-tratamento de lixiviados de aterros sanitários.

Aplicação de processos físico-químicos como alternativa de pré e pós-tratamento de lixiviados de aterros sanitários.

A utilização da operação de stripping para redução da carga de amônia de lixiviados de aterros sanitários a montante de sistemas bio- lógicos de tratamento é especialmente atrativa, uma vez que o efluen- te bruto possui, normalmente, valores de pH elevados (pH>8,5), o que torna desnecessária a adição de alcalinizante e, de certo modo, desonera o processo de tratamento. Portanto, ao longo do experi- mento, o valor do pH na massa líquida era aquele do próprio lixivia- do bruto em ambos os sistemas de tratamento.

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VOLTAMMETRIC BEHAVIOR OF SOME STEELS IN AQUEOUS SOLUTIONS OF HNO3

VOLTAMMETRIC BEHAVIOR OF SOME STEELS IN AQUEOUS SOLUTIONS OF HNO3

The electrochemical studies pointed out that the seven alloys considered are very close not only from the chemical composition, but also from the structural one, and the different microelements do not signifi cantly change the voltammetric behavior. Yet, for given steels, it was noticed that the corrosion potential (E corr ) is higher in the case if the aggressive medium of HNO 3 has a lower concentration. This may be explained by the appearance of some iron oxide protection layers, which reduced the reaction rate on the steel surface undergoing corrosion, a fact that takes place faster when the HNO 3 concentration is higher.
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TECNOLOGIAS PARA A PRODUÇÃO E PURIFICAÇÃO DO PVC

TECNOLOGIAS PARA A PRODUÇÃO E PURIFICAÇÃO DO PVC

Atingida a conversão da reação, geralmente na faixa entre 75 e 95%, a reação é encerrada, e o monômero remanescente é recuperado. O polímero obtido na forma de lama (suspensão) passa, então, por um processo de stripping, no qual o MVC remanescente é extraído por meio de aplicação de vácuo e aumento de temperatura, tanto em reatores comuns quanto em torres, onde a lama é contatada com o vapor d’água em contracorrente. A lama passa, a seguir, por um processo de concentração via centrifugação, e o material úmido resultante é seco em secadores de leito fluidizado. A resina seca é, então, peneirada para retenção de partículas extremamente grosseiras e armazenada em silos, para posterior acondicionamento nos diferentes sistemas de distribuição, tais como sacaria de 25 kg, grandes sacos de 1,2 t ou mais e, até mesmo, em caminhões-silo. A Figura 1 mostra um esquema simplificado do processo de polimerização em suspensão.
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Statistical modeling of mixtures: a tutorial experiment using anodic stripping voltammetry.

Statistical modeling of mixtures: a tutorial experiment using anodic stripping voltammetry.

de medida para determinação de níquel usando a Voltametria de Redissolução Anódica (“Anodic Stripping Voltammetry, ASV”). Ri- gorosamente, as proporções dos solventes devem ser tomadas em termos de % m/m, pois o uso de proporções em massa elimina pro- blemas como variações de volume para misturas de diferentes pro- porções e possíveis efeitos de temperatura. Entretanto, para fins di- dáticos e para facilitar a preparação das soluções, as massas dos solventes em cada mistura podem ser convertidas para volumes, con- siderando-se suas densidades individuais aproximadas (d DMF = 0,94 g cm -3 , d
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REMOÇÃO DE ETANOL POR STRIPPING EMPREGANDO DIÓXIDO DE CARBONO CAMILA RAMOS DA SILVA PINTO

REMOÇÃO DE ETANOL POR STRIPPING EMPREGANDO DIÓXIDO DE CARBONO CAMILA RAMOS DA SILVA PINTO

Taylor et al. (1997), Silva (2007), Romanholi (2010), Esperança et al. (2012) e Sonego et al. (2014) estudaram a operação de stripping para arrastar etanol do meio líquido. Verificou-se em todos os trabalhos que, através do stripping, pode-se controlar a concentração de etanol da fase líquida pela sua retirada através do borbulhamento do gás de arraste. Portanto, o uso do stripping durante a fermentação alcoólica possibilita usar concentrações maiores de açúcares na alimentação das dornas, o que tem como consequência maior produção de etanol, para um mesmo volume de vinho, reduzindo o custo da destilação e da produção de vinhaça. Também a remoção de vapores do meio líquido acaba por diminuir a temperatura da fase líquida, podendo ser a operação de stripping uma fonte adicional de resfriamento do vinho durante o processo fermentativo, o que seria de grande interesse para as usinas, pois esse controle é bastante difícil, principalmente em dias com temperatura ambiente elevada. Além disso, o stripping poderia ser utilizado no vinho já fermentado para extrair o etanol, sendo uma alternativa à destilação, podendo reduzir o consumo de vapor da planta.
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J. Braz. Chem. Soc.  vol.25 número5

J. Braz. Chem. Soc. vol.25 número5

voltammetric determination of diltiazem. It was observed that for the same concentration, O-desacetyl diltiazem and N-desmethyl diltiazem have the same voltammetric response of diltiazem, appearing at the same potential (ca. −1.5 V) and presenting the same current intensity. This result is in accordance with the fact that the cathodic peak is to be due to a reduction of the oxo group. 22

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Voltammetric characterization of an iridium oxide-based system: the

Voltammetric characterization of an iridium oxide-based system: the

continuous cyclization of the potential between 0.0 and 1.4 V per ERH to 20 mV s 1 . The purpose was to investigate the stability of the oxide layers in this new condition. While the voltammetric current for the electrode prepared at 400 8C decreases continually with n -values, the other electrodes do not show any change in the voltammetric behavior. This result sug- gests that while the process of the Mn dissolution occurs in a continuous and slow way for the electrode prepared at 400 8C, for the other samples this process is very fast and occurs soon after the first cycles.

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Applicability of a Voltammetric Assay Based on the Electroreduction of Oxygen to

Applicability of a Voltammetric Assay Based on the Electroreduction of Oxygen to

Among the three in vitro assays applied, ABTS, DPPH and DPV, the best result for antioxidant capacity of the pequi pulp was obtained by the voltammetric test and expressed in trolox standard equivalent. Therefore, this protocol was efficient to evaluate the antioxidant capacity. It is also an alternative methodology to carry out this analysis, mainly for providing relevant information for the redox process that cannot be obtained from the traditional spectrophotometric assays.

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J. Braz. Chem. Soc.  vol.24 número11

J. Braz. Chem. Soc. vol.24 número11

solution, using a µautolab III potentiostat/galvanostat. The voltammetric measurements were performed in a cell with three electrodes, using a modified glass carbon or bare glass carbon (geometric diameter = 0.2 cm) as the working electrode (previously polished with alumina), a saturated Ag/AgCl as the reference electrode, a platinum electrode as the auxiliary electrode. The glass carbon and the platinum electrode were polished with alumina before use. Under these conditions, ferrocene is oxidized at 0.43 V (Fc + /Fc). Elemental analyses were performed at

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Identificação microquímica de minerais primários de potássio no solo.

Identificação microquímica de minerais primários de potássio no solo.

Esse meio, cuja finalidade é fixar os minerais em lâminas permanentes, para posteriores tratamentos químicos, é preparado a partir de u m adesivo especial (weather stripping cement).[r]

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