Detection of chromium and vanadium is of interest for biomedical and environmental applications. The two metals have narrow limits between being essential and toxic for humans. Ultra-sensitive techniques have been studied to measure Cr and V at low concentrations found in human blood and environmental samples. Bismuth film and mercury-alloy electrodes have been developed as alternatives to traditional Hg-based electrodes for Cr and V detection. While catalytic adsorptive stripping voltammetry (CAdSV) has been used to detect Cr and V, little is known about the process. The mechanisms of CAdSV have been probed to provide a better understanding of its exceptional sensitivity and selectivity. Near-real time monitoring of plume gas constituents is desired as a diagnostic tool for combustion efficiency, ensuring safe testing conditions and observing releases of green house gasses. Ground testing rockets is a crucial preliminary step that ensures their performance during critical space missions. Optical sol-gel sensors for carbon dioxide have been developed for remote sensing applications. They are inexpensive and are compatible with the harsh environments encountered during rocket plume tests. The sensors are a viable approach to compliment current infrared (IR) measurements for real-time carbon dioxide detection. Additional work on kerosene and isopropyl alcohol sensing has been explored for incorporation into a multi-analyte sensing platform.

Development and studies of new electrochemical methods for the detection of various biologically and environmentally relevant substances are the focus of this dissertation. A dual amperometric sensor, capable of the simultaneous, real-time determination of NO and O,2, has been developed and optimized. Many tests were performed in order to reduce cross-talking between the two sensors, and an electro-deposited polymer, poly-5-amino-1-naphthol, was shown to reduce the cross-talking to insignificant levels. The use of bismuth-based electrodes in the detection of various metals has been explored. A bismuth bulk electrode has been developed, optimized, and used for the individual and simultaneous determination of Pb(II), Cd(II), and Zn(II). The fundamental electrochemistry of several bismuth-based electrodes in the system used for Cr(VI) analysis has also been explored, and many interactions among the electrode material, ligand, and analyte were observed, particularly the formation of a soluble bismuth-ligand complex. Electrochemical analysis of Cr(VI) was attempted at all of the bismuth-based electrodes, with success at the thin bismuth film electrode. A series of surface modifications were made to the glassy carbon substrate, in an attempt to remove any co-adsorbed contaminants and to understand the sensitivity of the chromium detection process. Inevitably, it was found that the contaminating source was contaminants in the nitrogen gas used for solution deaeration. Upon switching to argon, detection became highly reproducible and showed strong linearity with the Cr(VI) concentration.

Voltammetric methods for the determination amphenicol antibiotic chloramphenicol (CAP) and quinolone antibiotic Ofloxacin (OFL) were developed. TTechniques differential pulse voltammetry (DPV) and DC voltammetry (DCV) for determination of both substances at boron doped diamond film electrode (BDDFE) were used. The effect of pH of Britton-Robinson buffer was tested and the stability of the signal with repeated measurements was monitored. Optimal pH 6 was used for determining of CAP by both, DPV and DCV techniques. Media of pH 4 for determining of OFL by DPV and DCV was optimal. Under these conditions linear dependences in the calibration concentration region 1.10 -6 - 1.10-4 mol.l -1 were obtained. The limit of determination for the method for CAP by DPV at 3.10 mol.l , by -6 -1 DCV at 3.10 mol.l and for -6 -1 OFL by DPV at 1.10 mol.l -6 -1 and by DCV at 4.10 mol.l -7 -1 was found. The developed methods were used for the determination of CAP in the drug samples Spersadex comp. and OFL determination in drug samples Zanocin 200. Method for solid phase extraction of OFL from samples of urine with voltammetric detection was developed with limit of determination at 7.10 mol.l . -6 -1

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Single sensitive sequential AdSV methods were developed and optimized for the determination of trace zirconium, vanadium, titanium and molybdenum in river, estuary and seawater, independent of the salinity and content of organic matter in the sample. The methods are based on the accumulation of Zr(IV)-and V(V)-cupferron-oxalic acid-1,3-diphenylguanidine complexes and the accumulation of Ti(IV)-and Mo(VI)-mandelic acid at the hanging mercury drop electrode (HMDE). Differential pulse, adsorption potential of -0.6, -0.2, -0.1 and -0.1 V (vs. Ag/AgCl), adsorption time of 400, 20, 120 and 1 s and scan rates of 0.01, 0.06, 0.02 and 0.02 V s-1 for Zr(IV), V(V), Ti(IV) and Mo(VI), respectively, were used as instrumental parameters. The reduction peak for the complexes of Zr(IV), V(V), Ti(IV) and Mo(VI) appeared nearly -0.95, -0.65, -0.85 and -0.4 V, respectively. The variations of the peak current as well as the peak potential of each metal complexes were plotted against the apparent ionic strengths. The proposed voltammetric methods were applied in German and Brazilian rivers and estuaries as well as in seawater from the North Sea collected at the north of Germany and the Atlantic Ocean, collected during scientific cruise between Chile and Germany, as interesting and very simple alternatives to very laborious and time-consuming pre-existent methods, based on outline pre-concentration and separation from the matrix and subject to external contamination. The limits of detection and determination were in the range of ppt-levels and the methods accuracy were evaluated by recoveries tests and by measuring V(V) and Mo(VI) in two NRCC reference materials. Estuarine mixtures experiments were also carried out with the aim to get more insight on the distribution of Ti(IV), Zr(IV), Mo(VI) and V(V) along the estuaries of the rivers Rhine, Weser and Elbe with the North Sea. In this context, natural fresh waters were mixed with seawater at different ratios. / Métodos sensíveis e sequenciais de voltametria adsortiva de redissolução foram desenvolvidos e otimizados para a determinação de traços e ultra-traços de zircônio, vanádio, titânio e molibdênio em águas de rio, estuário e mar, independentemente da salinidade e conteúdo de matéria orgânica na amostra. Os métodos são baseados na acumulação de complexos de Zr(IV) e V(V) com cupferron-ácido oxálico-1,3-difenilguanidina e de complexos de Ti(IV) e Mo(VI) com ácido mandélico no eletrodo de mercúrio de gota pendente (HMDE). Pulso diferencial, potenciais de adsorção de -0,6; -0,2; -0,1 e -0,1 V (vs Ag/AgCl), tempos de adsorção de 400, 20, 120 e 1 s e velocidades de varredura de 0,01; 0,06; 0,02 e 0,02 V s-1, para Zr(IV), V(V), Ti(IV) e Mo(VI), respectivamente, foram usados como parâmetros instrumentais. Os picos de redução para os complexos de Zr(IV), V(V), Ti(IV) e Mo(VI) surgiram próximos de -0,95; -0,65; -0,85 e -0,4 V, respectivamente. As variações de corrente de pico assim como de potencial de pico de cada complexo dos metais foram plotados contra as forças-iônicas aparentes das amostras. Os métodos voltamétricos propostos foram aplicados em águas de rio e estuário coletadas na Alemanha e no Brasil e em amostras de água do mar do Mar do Norte coletadas no norte da Alemanha e Oceano Atlântico, coletadas durante expedição científica entre o Chile e Alemanha. Estes métodos se mostraram ser alternativas simples a métodos bastante complexos e demorados, baseados em pré-concentração outline e separação da matriz, sujeitos a contaminação externa. Os limites de detecção e quantificação estavam na ordem de partes por trilhão e a exatidão dos métodos foi avaliada através de teste de recuperação de amostras adicionadas com os analitos em estudo e em 2 materiais de referência certificados. Também foram realizados experimentos de mistura estuarina com o objetivo de obter informações da distribuição de Ti(IV), Zr(IV), Mo(VI) e V(V) ao longo de estuários dos rios Reno, Weser e Elba com o Mar do Norte. Neste intuito, as águas dos rios e do mar foram misturadas em diferentes razões.

Made available in DSpace on 2016-08-19T12:56:36Z (GMT). No. of bitstreams: 1 dissertacao Eva.pdf: 1581206 bytes, checksum: 1aebd130343ea1ba16d040c34b337e22 (MD5) Previous issue date: 2011-07-04 / The presence of metals in biodiesel can be related to raw material, the process used to obtain biodiesel or its storage and can cause reactions of oxidation, corrosion and clogging engines, besides causing risks to human health and the environment. In this paper, we propose a procedure based on voltammetric experimental conditions suitable for the determination of Ni2+ ion in biodiesel (B100) through Square Wave Adsorptive Stripping Voltammetry, using the mercury film electrode prepared ex situ. First, the mercury film was prepared and then was conducted the analysis of a biodiesel pre-treated (digested) sample. The sample digestion was performed with microwave oven in a closed system in the presence of ultra-pure nitric acid and hydrogen peroxide. After this, ammonia buffer 0.01 mol L-1 pH 9.23 and NaOH 0.46 mol L-1 was added into the cell to adjust the pH of the sample to a final value of approximately 9.2. Finally, the chelator dimethylglyoxime (DMG) 0.01 mol L-1 was added, which acts as a complexing element to capture the Ni2+ ion. Next, several voltammetric experiments, in the absence and presence of increasing aliquots of biodiesel and standard solution of the metallic ion, were performed to optimize the analysis conditions. The results indicate that the Square Wave Adsorptive Stripping Voltammetry (VAdRSWV) appeared suitable for measurements of trace metal in Biodiesel (B100) in concentrations up to 10-8 mol L-1. The experiments carried out by successive addition of aliquots of a standard solution of Ni2+ ions provided a linear response of peak current with the concentration of metal ion. Each sample of biodiesel was analyzed in triplicate, with very satisfactory results from the analytical point of view, once we were dealing with trace element analysis, especially in terms of accuracy (recovery 105%) and precision (RSD 9.61%) for the Ni2+ metal ion, using a confidence limit of 98%. / A presença de metais no biodiesel pode estar relacionada com a matéria-prima, com o processo utilizado para a obtenção do biodiesel ou com sua estocagem e pode provocar reações de oxidação, corrosão e entupimento em motores, além de causar riscos à saúde humana e ao meio ambiente. Neste trabalho, é proposto um procedimento voltamétrico com base em condições experimentais adequadas para a determinação do íon Ni2+ em biodiesel (B100) por Voltametria Adsortiva de Redissolução no modo Onda Quadrada, usando o eletrodo de Filme de Mercúrio preparado no modo ex situ. Inicialmente, o filme de mercúrio foi preparado e a seguir realizaram-se as análises com amostra de biodiesel pré-tratada (digerida). A digestão da amostra foi realizada com forno de micro-ondas em sistema fechado, na presença de ácido nítrico ultra-puro e peróxido de hidrogênio. Após essa etapa, foi adicionado tampão amônia 0,01 mol L-1 pH 9,23 e NaOH 0,46 mol L-1 na célula para ajustar o pH da amostra para um valor final de aproximadamente 9,2. Por fim, foi adicionado o quelante dimetilglioxima (DMG) 0,01mol L-1 que funciona como complexante para captura do íon Ni2+. Após esta etapa, vários experimentos voltamétricos, na ausência e presença de alíquotas crescentes de biodiesel e solução padrão do íon metálico foram realizados para otimizar as condições de análise. Os resultados obtidos indicam que a Voltametria Adsortiva de Redissolução no modo Onda Quadrada (VAdRSWV) apresentou resultado satisfatório para medidas do metal traço em Biodiesel (B100), em concentrações de até 10-8 mol L-1. Os experimentos realizados pela adição sucessiva de alíquotas de uma solução padrão do íon Ni2+ proporcionaram uma resposta linear da corrente de pico com a concentração do íon metálico. Cada amostra de biodiesel foi analisada em triplicata, apresentando resultados bastante satisfatórios do ponto de vista analítico por se tratar de análise de elementos traços, principalmente, em termos de exatidão (recuperação de 105 %) e precisão (DPR de 9,61%), para o íon metálico Ni2+, utilizando um limite de confiança de 98%.

Philosophiae Doctor - PhD / The need for clean, non-toxic drinking water supplies, free of pollutants and metal contamination is vital in impoverished areas and the developing world alike. With this in mind, the development of accurate, inexpensive, portable and simple devices for remote sensing applications is therefore pivotal for early detection and the prevention of illnesses. Over the last two decades, adsorptive stripping voltammetry (AdSV) has emerged as a superior detection method over common analytical techniques due to its low-cost instrumentation, unskilled labour and ability to detect a wide range of analytes. / 2020-08-31

This diploma thesis is focused on the determination of chloramphenicol by differential pulse voltammetry (DPV), DC voltammetry (DCV), cyclic voltammetry (CV) and adsorptive stripping voltammetry (AdSV) on a meniscus modified silver solid amalgame electrode (m- AgSAE). For the determination of chloramphenicol the optimum conditions were found and under these conditions concentration dependences were measured and then limits of quantification were determined. The influence of pH of BR buffer was tested. For determination of chloramphenicol by DCV pH 7 was chosen as an optimum background and pH 8 was chosen as an optimmum for DPV determination. Under these conditions linear dependences were obtained in the concentration range of 1·10-6 - 1·10-4 mol·l-1 . The limit of detection of chloramphenicol by DCV was 2.3·10-6 mol·l-1 . The limit of detection of chloramphenicol by DPV was 2.1·10-6 mol·l-1 in distilled water, 2.9·10-6 mol·l-1 in river water and 4.2·10-6 mol·l-1 in drinking water. Electrochemical behavior of chloramphenicol was studied by cyclic voltammetry in BR buffer with pH 2, 6, 8, 12 and then mechanism of reduction of chloramphenicol was propose based on available literature. Chloramphenicol was determined in drug Spersadex by DPV in BR buffer with pH 8. The optimal conditions for determining...

The submitted work deals with the application of voltammetric determination of Fomesafen using non-traditional mercury meniscus modified silver solid amalgam electrode on model samples of Fomesafen in real aqueous matrices of drinking and river water. This method of measurement has been developed and optimized in my bachelor thesis, which the diploma thesis is related to. Fomesafen belongs to a group of herbicides used on a mass scale in the late 20th century in the USA and in many countries around the world still used even today. Among its side effects according to the EPA include, among others, potential carcinogenicity to humans and confirmed carcinogenicity to some mammals (such as rats) which led to a legislative regulation on its use in many countries around the world including the USA, the European Union and many others. Silver solid amalgam electrode has been developed with the intention to limit the use of mercury in accordance with new legislation of the European Union and the concept of green analytical chemistry. Despite the low levels of mercury mainly bound in the form of virtually harmless silver amalgam electrode retains very similar electrochemical properties with proven mercury electrodes. As part of the thesis, direct determination of a number of partial extraction of Fomesafen...

Цель работы состояла в определении оптимальных значений диаметра и массы углеродных нанотрубок (УНТ) в нафионсодержащей модифицирующей пленке для получения наилучших электрохимических и аналитических характеристик толстопленочных углеродсодержащих электродов (ТУЭ). В ходе работы синтезированы многостенные УНТ со средним диаметром dср ≈ 23 нм методом каталитического пиролиза этанола и проведена кислотная очистка полученного материала от металлических частиц катализатора и других модификаций углерода. Аналогичным способом обработаны коммерческие УНТ с dср ≈ 147 и 16 нм от Sigma-Aldrich. Успешно изготовлены 36 типов ТУЭ без УНТ и на основе УНТ в условиях варьирования массового содержания УНТ в диапазоне MУНТ = 0,3-10,0 мкг на поверхности ТУЭ. Аттестация поверхностей электродов проведена методами оптической и электронной микроскопии. Изучены электрохимические характеристики изготовленных ТУЭ методами циклической вольтамперометриии и импедансной спектроскопии. Выполнено определение ионов железа (III) в модельном растворе методом адсорбционной инверсионной вольтамперометрии. Установлены оптимальные значения среднего диаметра УНТ dср ≥ 23 нм и массы УНТ MУНТ = 5,0-10,0 мкг на поверхности ТУЭ для получения наилучших электрохимические и аналитические характеристики. Разработанные ТУЭ на основе УНТ могут применяться для определения ионов тяжелых металлов в реальных водах с концентрацией меньшей предельно-допустимых значений, установленных нормативными документами. / The aim is to determine the optimal values of the diameter and weight of carbon nanotubes (CNT) in modifier film containing Nafion for the best electrochemical and analytical characteristics of the thick film of carbon-containing electrodes (TFCE). Multi-walled CNT with an average diameter dav ≈ 23 nm were synthesized by the catalytic pyrolysis of ethanol and purified from the metal catalyst particles and other modifications of carbon, using mixture of concentrated sulfuric and nitric acids. Commercial CNT with dav ≈ 147 and 16 nm from Sigma-Aldrich were treated by a similar procedure. The batch of 36 types of TFCE without CNT and based on CNT varied by weight of CNT (MCNT) on TFCE surface in the range of 0,3-10,0 μg was made. The electrode surfaces were studied by optical and electron microscopy. The electrochemical characteristics of obtained TFCE by cyclic voltammetry and electrochemical impedance spectroscopy were investigated. The detection of Fe (III) ions in a model solution was carried out by adsorptive stripping voltammetry. The optimal values of the average diameter of CNT dav ≥ 23 nm and a weight of CNT on TFCE surfaces MCNT = 5,0-10,0 μg were determined. These parameters allow us to reach the best electrochemical and analytical characteristics of modified TFCE. Developed TFCE based on CNT may be used for the detection of heavy metal ions in real water with a concentration of less maximum permissible values, established by regulations.

Presented Diploma Thesis is focused on electroanalytical determination of the herbicide Aclonifen, which belongs to a group of herbicides derived from diphenylether. These herbicides are used due to their effects - inhibition of protoporfyrinogen oxidase synthesis and also inhibition of biosynthesis of carotenoids. Due to its widespread use in agricultural, toxical effects on humans and because of its negative impacts particularly on aquatic ecosystems there is a need for methods capable of determining the presence of Aclonifen in the environment to monitor its ecological impacts. Optimal conditions for the determination of Aclonifen have been investigated in BR buffer - methanolic solution and in BR buffer. Electrochemical behavior of the substance has been studied using direct current voltammetry (DCV), differential pulse voltammetry (DPP) and adsorptive stripping voltammetry (AdSV) on the hanging mercury drop electrode (HMDE) and by using TAST polarography and differential pulse polarography (DPP) on the dropping mercury electrode (DME). UV/VIS spectrophotometric detection was used for comparison to electrochemical detection. Used wavelengths were 308 nm and 388 nm. For electrochemical determination of Aclonifen the above mentioned techniques were used and following results were obtained: DCV...