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Análise de cádmio e chumbo em bijuterias por espectrometria de absorção atômica por chama (F AAS) e voltametria de pulso diferencial (VPD)Ferreira, Taimara Polidoro 25 February 2016 (has links)
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Previous issue date: 2016-02-25 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A análise de metais em diversos tipos de amostras, já é algo bem descrito na literatura utilizando a espectrometria de absorção atômica, que é a técnica mais popular para este tipo de análise, entretanto o desenvolvimento de técnicas eletroanalíticas para a análise de metais é algo que vem crescendo nos últimos anos. As técnicas eletroanalíticas apresentam as vantagens de conseguirem determinar baixas concentrações de metais, permitirem a determinação simultânea destes e ainda possuírem um baixo custo se comparada à técnicas espectrométricas.
Devido ao aumento da preocupação da qualidade dos metais para a confecção de bijuterias, a análise de metais se torna extremamente importante uma vez que altas concentrações desses metais no organismo, em especial metais tóxicos como cádmio e chumbo, podem trazer malefícios irreversíveis para a saúde.
Neste contexto, o objetivo do trabalho foi analisar cádmio e chumbo em amostras de bijuterias por voltametria de pulso diferencial (VPD) com etapa de pré-concentração e comparar com as análises por espectrometria de absorção atômica com chama (F AAS). Os parâmetros utilizados para a análise por voltametria de pulso diferencial foram: o potencial de deposição de -0,9 V com duração de 120 s e a faixa de potencial de -0,9 a 0,1 V. Dois tipos de digestão para as amostras foram testadas, em chapa de aquecimento e em um equipamento de micro-ondas, e após as digestões, as amostras foram analisadas pelas duas técnicas. A digestão por micro-ondas se mostrou mais adequada, assim como as análises por voltametria que apresentaram boa exatidão, que foi avaliada através de estudos de adição e recuperação, com resultados entre 99 a 110% para o cádmio e 99 a 105% para o chumbo. As amostras de bijuterias analisadas pela VPD e digeridas por micro-ondas continham de < LD a 4,05 % m/m de cádmio e de 0,004 a 7,55 % m/m de chumbo.
Os limites de detecção foram de 0,75 mg L-1 para o cádmio e de 0,07 mg L-1 para o chumbo para a técnica de absorção atômica e os limites de detecção para a voltametria foram de 0,02 mg L-1 para o cádmio, e de 2,26.10-3 mg L-1 para o chumbo. / The metal analysis of various types of samples, using atomic absorption spectrometry, is well described in the literature. It is the most popular technique for this type of analysis; however the development of electroanalytical techniques for the analysis of metals has been growing in recent years. The electroanalytical techniques have the advantages of be able to determine low concentrations of metals, allow the simultaneous determination of these and have low cost compared to spectrometric techniques. Due to the increased concern for quality of metals for the manufacture of jewelry, the metal analysis is extremely important since high concentrations of these metals in the body, in particular toxic metals such as cadmium and lead can bring irreversible harm to health. In this context, the aim of this study was to analyse cadmium and lead in jewelry samples by differential pulse voltammetry (DPV) with pre-concentration step and compare the results with atomic absorption spectrometry with flame (F AAS). The parameters used for the analysis by differential pulse voltammetry were: deposition potential = -0.9 V, deposition time = 120 s and the potential range from -0.9 to 0.1 V. Two types of samples digestion were tested: hot plate and microwave equipment. After digestions, the samples were analyzed by both techniques (DPV and F AAS). Digestion by microwave proved most suitable, as well as voltammetry results that showed good accuracy, which was evaluated by adding and recovery studies with results from 99 to 110% for cadmium and 99 to 105% for lead. Samples of jewelry and analysed by the DPV digested microwave contained the <LOD to 4.05 % w / w cadmium and 0.004 to 7.55 % w / w of lead. The limits of detection were 0.75 mg L-1 for cadmium and 0.07 mg L-1 for lead for atomic absorption technique and limits of detection for voltammetry was 0.02 mg L-1 for cadmium, and 2.26.10-3 mg L-1 for lead.
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In Situ Induction Heating of Electrodes and ApplicationsRahman, Mohammad Azizur 10 August 2018 (has links)
This thesis describes the fabrication of an induction heating apparatus and its use to directly heat small platinum and gold electrodes in electrolyte solution. The heating characteristics of the electrodes were studied via the entropic shift of redox potential with temperature and change in Faradaic current. Temperature pulse voltammetry (TPV) and cyclic voltammetry were used for temperature calibration under various heating conditions. The maximum temperature reached at a 0.25 mm diam platinum electrode surface in solution was 84 degrees C. At heated electrodes an increase in current was found to be due to convection and diffusion. TPV was performed with inductively heated gold (0.5 mm diam) and platinum electrodes, which gave complete current-potential-temperature information. Induction heated Pt electrodes were employed to investigate the kinetics and mass transfer process of oxygen reduction reaction (ORR) in acidic and alkaline media.
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Investigation of the ORR at PEM Fuel Cell Electrodes: Catalysis, Pulse Voltammetry & High Temperature ApplicationsPietrasz, Patrick 17 May 2010 (has links)
No description available.
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Kinetic Studies and Electrochemical Processes at Fuel Cell ElectrodesStuckey, Philip A. January 2011 (has links)
No description available.
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Voltametrické stanovení anilazinu na stříbrné tuhé amalgámové elektrodě / Voltammetric determination of anilazine on silver solid amalgam electrodeBystrianský, Martin January 2012 (has links)
Anilazine (4,6-dichloro-N-(2-chlorophenyl)-1,3,5-triazin-2-amine) is a fungicide from a group of triazine pesticides. These have been very widely used but for their toxicity for water environment they are being cancelled. Use of anilazine is not allowed anymore in the European Union. However, traces of its residues are able to find in environmental samples. The diploma thesis deals with determination of anilazine using silver solid amalgam electrode modified by mercury meniscus (m-AgSAE). Differential pulse voltammetry was used. For the determination, an acidic solution is necessary. In the work Britton-Roninson buffer pH = 2 was used. This is because of electrochemical reduction of anilazine (and other triazines) which is started by protonization of heterocycle ring. Anilazine exhibits one single well-defined peak, the potential of the peak was about Ep = -827 mV (vs. 3 mol l-1 argentochloride electrode). The limit of quantification achieved in surface water was 2 µmol.l-1. Other two possibilities of getting lower limit of quantification were examined - Adsorptive Stripping Voltammetry (AdSV) and preconcentration by Solid Phase Extraction (SPE). Using AdSV the limit of quantification LQ = 0,5 µmol.l-1. Conditions of adsorption were as following: Eacc = -100 mV, tacc = 60 s. For SPE, 200-mg columns...
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Développement de polymères à empreintes moléculaires électrochimiques pour la surveillance en micropolluants organiques des eaux dans les ouvrages du Canal de Provence / Development of an electrochemical molecularly imprinted polymer for the surveillance of organic micro pollutants in the water of Canal de ProvenceUdomsap, Dutduan 14 November 2014 (has links)
La technique de l’impression moléculaire permettant d'obtenir des polymères hautement sélectifs est utiliséedans de nombreuses applications. Dans le cadre de cette thèse, cette technique est employée pour préparer despolymères spécifiques du benzo(a)pyrène (BaP) en vue d’une application capteur. L’introduction d’une sonderédox au sein même du réseau de polymère offre la possibilité d’une détection directe de la cible, par unetechnique électrochimique. Dans le domaine des MIPs, ce travail est le premier à décrire l’utilisation d’unmonomère participant à la formation du réseau tridimensionnel tout en apportant une propriété rédox. Lespolymères synthétisés par polymérisation par précipitation ont été caractérisés en termes de composition, destabilité thermique et de propriétés texturales. Les propriétés de rétention ont été évaluées en mode batch parHPLC-UV en présence de BaP et d'interférents de type hydrocarbures aromatiques polycycliques. Ces MIPsprésentent de bonnes propriétés d’adsorption vis-à-vis du BaP avec des facteurs d’empreinte supérieurs à 1montrant l’efficacité de l’impression. Ces propriétés sont conservées en présence d’une matière organique (seld’acide humique), mais également après plusieurs cycles d’utilisation. Les analyses électrochimiques ontdémontré que les propriétés électrochimiques de ces MIPs diffèrent selon la présence ou pas de la cible avecune limite de détection de 0,09 μM en BaP, ouvrant la porte à la réalisation de capteurs. / Molecularly Imprinted Polymers show highly selective affinity towards the target molecule and are used inmany applications. In this context, the technology is used for preparing selective polymers for benzo(a)pyrene(BaP) with the aim of sensor fabrication. The addition of a redox tracer inside the polymer allows thepossibility of direct target detection by an electrochemical technique. In the MIP field, this work is the firstreporting the use of a functional monomer that not only participates in the creation of the polymer network butalso provides a redox property. The polymers synthesized using precipitation polymerization technique werecharacterized in terms of composition, thermal stability and textural properties. The adsorption properties wereevaluated in batch mode by HPLC-UV in the presence of BaP and interfering polycyclic aromatichydrocarbons. These MIPs show good adsorption behavior towards BaP with imprinting factors superior to 1showing the efficiency of the molecular imprinting. These properties were also preserved even in presence ofan organic matter (humic acid salt), and also after several uses. Finally, electrochemical analysis showed thatthese MIPs had a different electrochemical behavior depending on the presence or the absence of the targetwith a detection limit of 0.09 μM for BaP. The use of such electrochemical MIPs can thus be interestinglyconsidered in sensor devices.
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Aplica??o das t?cnicas eletroanal?ticas (voltametria c?clica e de pulso diferencial) usando o eletrodo de diamante dopado com boro para o estudo da isoniazida, etambutol, rifampicina e pirazinamidaOliveira, Severina Denise Sales de 31 July 2013 (has links)
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Previous issue date: 2013-07-31 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this work a study was done using electrochemical cyclic voltammetry and
differential pulse voltammetry for isoniazida (INH), ethambutol (EMB), rifampicina
(RIF) and pyrazinamide (PZA) using the electrode boron-doped diamond (BDD) as
working electrode. It also verified the applicability of the technique of differential pulse
voltammetry in the quantification of the active compounds used in the treatment of
tuberculosis, subsequently applying in samples of pharmaceutical formulation.
Among the four active compounds studied, isoniazid showed the best results for the
detection and quantification using differential pulse voltammetry. At pH 4 and pH 8,
for the calibration curves to INH showed good linearity, with quantification limits of
6.15 mmol L-1 (0,844 ppm) and 4.08 mmol L-1 (0.560 ppm) for the respective pH. The
proposed method can be used to determine drug isoniazid, for recovery values were
obtained in approximately 100% / Neste trabalho foi feito um estudo eletroqu?mico utilizando a voltametria c?clica
e voltametria de pulso diferencial para os f?rmacos isoniazida (INH), etambutol
(EMB), rifampicina (RIF) e pirazinamida (PZA) usando o eletrodo de diamante
dopado com boro (BDD) como eletrodo de trabalho. Foi tamb?m verificado a
aplicabilidade da t?cnica de voltametria de pulso diferencial na quantifica??o dos
princ?pios ativos usados no tratamento da tuberculose, posteriormente aplicando em
amostras de formula??o farmac?utica. Dentre os quatro princ?pios ativos estudados,
a isoniazida apresentou os melhores resultados de detec??o e quantifica??o com o
uso da voltametria de pulso diferencial. Em pH 4 e pH 8, as curvas de calibra??o
para a INH apresentaram boa linearidade, apresentando os limites de quantifica??o
de 6,15 μmol L-1 (0,844 ppm) e 4,08 μmol L-1 (0,560 ppm), para os respectivos pH. O
m?todo proposto pode ser usado para a determina??o de isoniazida em f?rmacos,
pois foram obtidos valores de recupera??o em torno de 100%
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Aplicabilidade da voltametria de pulso diferencial na quantifica??o de ?cido f?lico e ?cido ox?lico: um m?todo comparativoAraujo, Eliane Gon?alves de 04 December 2013 (has links)
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Previous issue date: 2013-12-04 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The development of more selective and sensitive analytical methods is of great importance in
different areas of knowledge, covering, for example, food, biotechnological, environmental
and pharmaceutical sectors. The study aimed to employ the technique electroanalytical
differential pulse voltammetry (DPV) as an innovative and promising alternative for
identification and quantification of organic compounds. The organic compounds were
investigated in this study oxalic acid (OA) and folic acid (FA). The electrochemical oxidation
of oxalic acid has been extensively studied as a model reaction in the boundary between the
organic and inorganic electrochemistry. Since the AF, an essential vitamin for cell
multiplication in all tissues, which is essential for DNA synthesis. The AF has been
investigated using analytical techniques, liquid chromatography and molecular absorption
spectrophotometry. The results obtained during the experimental procedure indicated that the
process of electrochemical oxidation of oxalic acid is strongly dependent on the nature of the
anode material and the oxidation mechanism, which affects their detection. Efficient removal
was observed in Ti/PbO2 anodes, graphite, BDD and Pt 90, 85, 80 and 78% respectively. It
was also shown that the DPV employing glassy carbon electrode offers a fast, simple, reliable
and economical way to determine the AO during the process of electrochemical oxidation.
Furthermore, electroanalytical methods are more expensive than commonly used
chromatographic analysis and other instrumental methods involving toxic reagents and higher
cost. Compared with the classical method of titration and DPV could be a good fit, confidence
intervals and detection limits confirming the applicability of electroanalytical technique for
monitoring the degradation of oxalic acid. For the study of AF was investigated the
electrocatalytic activity of the carbon paste electrode for identification and quantification in
pharmaceutical formulations by applying the DPV. The results obtained during the
experimental procedure showed an irreversible oxidation peak at 9.1 V characteristic of FA.
The carbon paste sensor showed low detection limit of 5.683?10−8 mol L-1 reducing matrix
effects. The spectrophotometric analysis showed lower concentrations of HF compared with
those obtained by HPLC and DPV. The levels of AF were obtained according to the
methodology proposed by the Brazilian Pharmacopoeia. The electroanalytical method (DPV)
proposed is cheaper than GC analysis commonly used by the pharmaceutical industry. The
results demonstrated the potential of these electroanalytical techniques for future applications
in environmental, chemical and biological sensors / O desenvolvimento de m?todos anal?ticos cada vez mais seletivos e sens?veis ? de grande
relev?ncia em diferentes ?reas do conhecimento, contemplando, por exemplo, os setores
aliment?cios, biotecnol?gicos, ambientais e farmac?uticos. O estudo teve como objetivo
empregar a t?cnica eletronal?tica voltametria de pulso diferencial (DPV) como uma alternativa
inovadora e promissora para identifica??o e quantifica??o de compostos org?nicos. Os
compostos org?nicos investigado neste estudo foram o ?cido ox?lico (AO) e o ?cido f?lico
(AF). A oxida??o eletroqu?mica do ?cido ox?lico tem sido extensivamente estudada como
uma rea??o modelo na fronteira entre a eletroqu?mica org?nica e inorg?nica. O AF ? uma
vitamina essencial na multiplica??o celular de todos os tecidos, indispens?vel ? s?ntese do
DNA, tem sido investigada empregando t?cnicas anal?ticas, com a cromatografia l?quida e a
espectrofotometria de absor??o molecular. No presente trabalho foi investigada a oxida??o
eletroqu?mica do AO em diferentes materiais eletrocatal?ticos. Os resultados obtidos durante o
procedimento experimental indicaram que o processo de oxida??o eletroqu?mica do ?cido
ox?lico ? depende fortemente da natureza do material an?dico e do mecanismo de oxida??o, o
que afeta a sua detec??o. Eficientes remo??es foram obtidas em ?nodos de Ti/PbO2, grafite,
BDD e Pt 90, 85, 80 and 78% respectivamente. Foi tamb?m demonstrado que a VPD
empregando eletrodo de carbono v?treo oferece uma maneira r?pida, simples, confi?vel e
econ?mica para determinar a AO durante o processo de oxida??o eletroqu?mica. Al?m disso,
os m?todos eletroanal?ticos s?o mais baratos do que a an?lise cromatogr?fica comumente
utilizada e que outros m?todos instrumentais envolvendo reagentes t?xicos e de custo mais
elevado. Comparado com o m?todo de titula??o cl?ssica e DPV conseguiu-se um bom ajuste,
intervalos de confian?a e limites de detec??o confirmando a aplicabilidade da t?cnica
eletroanal?tica para o monitoramento da degrada??o de ?cido ox?lico. Para o estudo
envolvendo o AF foi investigado a atividade eletrocatal?tica do eletrodo de pasta de grafite
para a sua identifica??o e quantifica??o em formula??es farmac?uticas aplicando a VPD. Os
resultados obtidos durante o procedimento experimental indicaram um pico de oxida??o
irrevers?vel em 9,1 V caracter?stico do AF. O sensor de pasta de grafite apresentou baixo
limite de detec??o 5,683?10−8 mol L-1 reduzindo os efeitos da matriz. As an?lises
espectrofotom?tricas apresentaram concentra??es de AF menor quando comparadas com os
dados obtidos por CLAE e VDP. Os teores de AF foram obtidos de acordo com a
metodologia proposta pela farmacopeia brasileira. O m?todo eletroanal?tico (VPD) proposto
apresenta menor custo e redu??o do tempo de an?lise, quando comparado com a
cromatografia l?quida, t?cnica comumente utilizadas pelas ind?strias farmac?uticas. Os
resultados demonstraram o potencial dessas t?cnicas eletroanal?ticas para futuras aplica??es
em sensores ambientais, qu?micos e biol?gicos
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DETERMINAÇÃO DO PARAQUAT SOBRE ELETRODOS DE CARBONO VÍTREO MODIFICADO COM FTALOCIANINA TETRASSULFONADA DE NIQUEL EM FILME DE POLI-L-LISINA / DETERMINATION OF THE PARAQUAT ON MODIFIED GLASS CARBON ELECTRODES WITH FTALOCIANINA TETRASSULFONADA OF NICKEL IN POLI-L-LISINA FILMMendes, Cristiane Arcângela de Souza 26 February 2007 (has links)
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Previous issue date: 2007-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work present an evaluation of a modified glassy carbon electrode with NiTSPc
immobilized with film PLL of the determination of paraquat by differential pulse
voltammetry. The film was formed applying 20μL of a solution prepared for the
mixture of equal volume of NiTSPc 0,8mM and poly-L-lisine (PLL) 0,12mM. The
maximum signal to noice ratio was obtained using a 0,1M Britton-Robinson buffer at
pH=7,0 as supporting electrolyte.. The electrode modified with NiTSPc/PLL
presented PQ reduction currents more accented and voltammetrics profiles better
with respect to the electrodes unmodified and modified with CuTSPc/PLL. The best
conditions of analyze had been amplitude of pulse 125mV, width of pulse 25mV,
speed of sweepings 10mV/s. The maximum relation signal noise was gotten in drain
plug Britton-Robinson 0,1M, with pH 7,0 as electrolyte has supported. This sensor
presented two reversible peaks for reduction of the PQ around - 0.71 V (peak 1) and
- 1,10 V (peak 2) versus E.C S. In these conditions, the modified electrode obtained a
linear response range from 1,00 x 10-6 to 1,00 x 10-5 mol L-1 with detection and
quantification limits equals to 7,58 x 10-8 mol L-1 (19,5 μg L-1) and 2,5 x 10-7 mol L-1
(64 μg L-1), respectively. The studied sensor presented values below 5%, in terms of
relative standard deviation, for repeatability (2,52% for N = 10) and
reproducibility (2,97% for N = 5) studies. The recovery in real samples was of 98%. / Este trabalho apresenta uma avaliação de um eletrodo de carbono vítreo modificado
com NiTSPc imobilizada com filme de poli-L-lisina para determinação do paraquat
por voltametria de pulso diferencial. O filme foi formado adiconando-se 20μL de uma
solução preparada pela mistura de volumes iguais de NiTSPc 0,8mM e PLL 0,12mM.
O eletrodo modificado com NiTSPc/PLL apresentou correntes de redução do PQ
mais acentuadas e melhores perfis voltamétricos em relação ao eletrodo não
modificado e modificados com CuTSPc/PLL. As melhores condições de analise
foram amplitude de pulso 125mV, largura de pulso 25mV, velocidade de varredura
10mV/s. A máxima relação sinal ruído foi obtida em tampão Britton-Robinson 0,1M,
com pH 7,0 como eletrólito suporte. Este sensor apresentou dois picos reversíveis
para redução do PQ em torno de - 0,71 V (pico 1) e - 1,10 V (pico 2) vs E C S..
Nestas condições, o eletrodo modificado obteve uma resposta linear de 1,00 x 10-6 a
1,00 x 10-5 mol L-1 com limites de detecção e quantificação iguais a 7,58 x 10-8 mol
L-1 (19,5 μg L-1) e 2,5 x 10-6 mol L-1 (64 μg L-1), respectivamente. O sensor estudado
apresentou valores abaixo de 5%, em termos de desvio padrão relativo, para
estudos de repetibilidade (2,52% para N = 10) e reprodutibilidade (2,97%
....para N = 5). A recuperação em amostras reais foi de 98%.
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Stanovení indikanu na uhlíkové pastové elektrodě a uhlíkové kompozitní elektrodě / Determination of indican on carbon paste electrode and on carbon composite electrodeBergerová, Michaela January 2017 (has links)
This thesis is focused on the application of two working electrodes of graphite suitable for determination of oxidizable tumour biomarkers. It deals with the study of electrochemical behavior of urinary indican. For the determination the technique of differential pulse voltammetry (DPV) was used on carbon paste electrode and film composite paste electrode in Britton-Robinson (BR) buffer. In the first step optimal conditions were determined to find the lowest limit of determination (LQ) of this substance. BR buffer of pH 3 was chosen as the optimum medium for determination on a carbon paste electrode and BR buffer of pH 2 was used as the optimum medium for the determinaton using a film composite electrode. Performance for both electrodes was observed in a concentration range of from 1 · 10-6 to 5 · 10-5 mol·l-1 . The limit of determination for measurements on a carbon paste electrode was 0.7 µmol·l-1 and the film composite electrode was 1.7 µmol·l-1 . Possibility of the acummulation of indican was examined in order to increase sensitivity and decrease of limit of quantification. However, after 5 minute sorption, no increase in response was observed and the accumulation step was not inserted. Developed method was tested on the determination of urinary indican in human urine matrix after solid phase...
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