<p>The interaction of carboxylic acids with copper is a phenomenon found both outdoors and, more commonly, indoors. The influence on copper of some carboxylic acids (formic, acetic, propionic, and butyric) have so far been studied at concentrations levels at least three or four orders of magnitude higher than actual indoor conditions (< 20 ppb, volume parts per billion), and with only limited emphasis on any mechanistic approach. In this licentiate study a unique analytical setup has been successfully applied for <i>in situ </i>characterization and quantification of corrosion products formed during initial atmospheric corrosion of copper in the presence of acetic, formic or propionic acid. The setup is based on monitoring mass changes by the quartz crystal microbalance (QCM) and simultaneously identifying the chemical species by infrared reflection-absorption spectroscopy (IRAS). Post-analysis of corrosion products was performed by coulometric reduction (mass of copper (I) oxide formed), grazing incidence x-ray diffraction (phase identification) and atomic force microscopy (surface topography).</p><p>The absolute amounts of mass of individual constituents in the corrosion products, mainly copper (I) oxide or cuprite, copper (II) carboxylate and water or hydroxyl groups, have been deduced<i> in situ</i> during exposure in 120 ppb of carboxylic acid concentration, 95% relative humidity and 20ºC. An overall result is the consistency of analytical information obtained. For copper (I) oxide the quantified data estimated from IRAS, QCM or coulomeric reduction agrees with a relative accuracy of 12 % or better.</p><p>The interaction of copper with the carboxylic acids seems to follow two spatially separated main pathways. A proton-induced dissolution of cuprous ions followed by the formation of copper (I) oxide, and a carboxylate-induced dissolution followed by the formation of copper (II) carboxylate. The first pathway is initially very fast but levels off with a more uniform growth over the surface. This pathway dominates in acetic acid. The second pathway exhibits a more constant growth rate and localized growth, and dominates in formic acid. Propionic acid exhibits low rates for both pathways. The difference between the carboxylic acids with respect to both total corrosion rate and carboxylate-induced dissolution can be attributed to differences in acid dissociation constant and deposition velocity.</p>

The interaction of carboxylic acids with copper is a phenomenon found both outdoors and, more commonly, indoors. The influence on copper of some carboxylic acids (formic, acetic, propionic, and butyric) have so far been studied at concentrations levels at least three or four orders of magnitude higher than actual indoor conditions (&lt; 20 ppb, volume parts per billion), and with only limited emphasis on any mechanistic approach. In this licentiate study a unique analytical setup has been successfully applied for in situ characterization and quantification of corrosion products formed during initial atmospheric corrosion of copper in the presence of acetic, formic or propionic acid. The setup is based on monitoring mass changes by the quartz crystal microbalance (QCM) and simultaneously identifying the chemical species by infrared reflection-absorption spectroscopy (IRAS). Post-analysis of corrosion products was performed by coulometric reduction (mass of copper (I) oxide formed), grazing incidence x-ray diffraction (phase identification) and atomic force microscopy (surface topography). The absolute amounts of mass of individual constituents in the corrosion products, mainly copper (I) oxide or cuprite, copper (II) carboxylate and water or hydroxyl groups, have been deduced in situ during exposure in 120 ppb of carboxylic acid concentration, 95% relative humidity and 20ºC. An overall result is the consistency of analytical information obtained. For copper (I) oxide the quantified data estimated from IRAS, QCM or coulomeric reduction agrees with a relative accuracy of 12 % or better. The interaction of copper with the carboxylic acids seems to follow two spatially separated main pathways. A proton-induced dissolution of cuprous ions followed by the formation of copper (I) oxide, and a carboxylate-induced dissolution followed by the formation of copper (II) carboxylate. The first pathway is initially very fast but levels off with a more uniform growth over the surface. This pathway dominates in acetic acid. The second pathway exhibits a more constant growth rate and localized growth, and dominates in formic acid. Propionic acid exhibits low rates for both pathways. The difference between the carboxylic acids with respect to both total corrosion rate and carboxylate-induced dissolution can be attributed to differences in acid dissociation constant and deposition velocity.

O presente trabalho versa sobre o desenvolvimento e a avaliação de três novas células espectroeletroquímicas para medidas de absorção na região do ultravioleta e visível, compatíveis com operação em fluxo, inclusive a técnica de FIA (Flow Injection Analysis). Características inerentes ao primeiro protótipo construído, tais como, geometria tubular, operação em fluxo ascendente e em condições de convecção forçada por vibração, separador ionomérico entre os eletrodos e detecção espectrofotométrica ex situ, permitiram a realização de estudos espectroeletroquímicos mesmo sob a decomposição paralela do solvente com intenso desprendimento de gases no eletrodo de trabalho. O desenvolvimento conjunto de eficiente dispositivo para remoção de bolhas possibilitou a obtenção de excelentes resultados espectrofotométricos. Abriu-se caminho para o estudo espectroeletroquímico de processos situados em regiões de potencial em que ocorre concomitante decomposição do solvente. Igualmente apropriado para a realização de estudos espectroeletroquímicos sob formação de gases, o segundo protótipo é de construção bastante semelhante ao primeiro, porém a elevada relação área do eletrodo de trabalho/volume de solução, conseguida principalmente pelo preenchimento da célula com fibras de carbono, foi capaz de promover eficiente conversão eletroquímica permitindo trabalho em condição de operação semi-coulométrica e conferindo à célula sensibilidade mais elevada que a do primeiro protótipo. O terceiro protótipo é do tipo camada delgada com caminho óptico longo, de aplicação restrita, pois, a regiões de potencial em que não há formação de gases. Características vantajosas frente às alternativas descritas na literatura são: uso de eletrodos de ouro planos (aproveitados de CDs regraváveis) de baixo custo e fácil construção, adaptação direta a cubatas convencionais de 1 cm de caminho óptico. Parâmetros experimentais como: potencial aplicado, concentração, vazão e volume injetado, foram investigados e avaliados com a finalidade de estabelecer as melhores condições de trabalho e funcionamento dos protótipos construídos visando posterior aplicação. / The present work discusses about the development and the evaluation of three new spectroelectrochemical cells for the UV-vis region, well suited for flow operation, including FIA (Flow Injection Analysis). Tubular geometry of the ionomeric separator of the electrode compartments, operation under ascending flow with convection increased by vibration and ex situ spectrophotometric detection after passage through an efficient debubbler granted excellent spectrophotometric results to the first prototype, even under intense gas evolution at the working electrode. This feature extends the spectroelectrochemical study to processes at extreme potential ranges. Equally appropriate for spectroelectrochemical studies under gas evolution, the second prototype presents geometry similar to the first one. However, filling of the tubular working electrode compartment with carbon fibers rendered higher ratio of electrode area/solution volume, promoting a more efficient electrochemical conversion, allowing semi-coulometric operation, and thus augmenting the sensitivity of the absorbance measurements. The third prototype is of the thin layer, long optical path type. Although not suitable for work under gas evolution, advantages of this cell in comparison with those described in the literature are: use of inexpensive flat gold electrodes, obtained from Au recordable CDs, installation in conventional cuvettes with an optical path of 1 cm, simple construction, perfect flow operation. Experimental parameters such as applied potential, analyte concentration flow rate and injected volume were inspected and analyzed for all assembled cells in a way that the best working conditions could be achieved.

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Background: Cystic fibrosis (CF) is a hereditary disorder caused by genetic mutations, which affect the chloride ion channels, leading to disrupted salt balance in different organs. A lack of properly functioning chloride ion channels can lead to formation of thick mucus, which hinders organ function, especially in the lungs where repeated inflammation occurs. Early diagnosis is critical to prevent further deterioration of the patient's condition. Current method of analysis of CF diagnostics uses conductivity meters to measure sweat electrolytes. However, current guidelines suggest using a chloridometer to directly measure chloride concentration, is the most reliable marker of cystic fibrosis. The aim of this project was to conduct a comprehensive evaluation of the new instrument's safety, reliability, validity, and conformity of the reference range to international chloride meter guidelines. Additional aims were to investigate the effect of storage conditions on sweat chloride concentration levels and examine the effect of increased salt intake on sweat test results. The study recruited healthy participants and took samples of their sweat by inducing sweat gland secretion. The chloride ion concentration was determined using a coulometric method. The results of the study found that the new method was reliable and matched international protocols. It also revealed that an increased salt consumption can impact chloride concentration in sweat, but not to an extent that it can affect medical decisions. Additionally, the study demonstrated that sweat samples can be frozen for up to two weeks without affecting the outcome of the chloride determination.

Carbon is due to its electrochemical properties a favourite material for construction of electrodes suitable for detection in flow system. The two most often used techniques (coulometric and amperometric) will be discussed in this Thesis. Carbon paste electrodes (CPE) represent the amperometric detectors. CPE are unstable in the medium with high content of organic solvents, which might complicate their application in HPLC, where the mobile phase contains organic component. It is interesting, that glassy carbon paste electrodes are more stable under such conditions. The change of surface and response of the electrode caused by the effect of methanol are described in this Thesis along with the possible reason of stability of GCPE. Roughing of the surface exposed to methanol is demonstrated by confocal microscopy. This effect leads to increase of height of the peak, background current and noise and to the shift of peak potential to less positive values. These changes are dependent on the time of exposure and the concentration of methanol. Coulometric detectors work with high conversion effectiveness and sensitivity, but in case of their passivation, reactivation is a relatively complicated problem, often leading to the replacement of electrode material. Answer to this problem can be given by using...

Die vorliegende Dissertation befasst sich mit drei Methoden, die zur elektrochemischen Charakterisierung von oxidischen Materialien bei erhöhten Temperaturen eingesetzt werden können: (i) der Sauerstoffaustauschmessung mittels coulometrischer Sauerstofftitration mit Festelektrolyt- gassensoren; (ii) der Hochtemperatur-Tubandt-Methode zum Nachweis von ionischer Leitfähigkeit in Festkörpern und (iii) der Impedanzspektroskopie an gesinterten Proben zur Bestimmung von materialspezifischen Eigenschaften von Korn und Korngrenze. Diese Methoden wurden genutzt, um diverse oxidische Substanzklassen zu untersuchen: den klassischen Sauerstoffionenleiter YSZ, das Halbleitermaterial SnO2 und ein nanostrukturiertes Komposit-Material aus Magnesiumoxid und mit Gadolinium dotiertem Ceroxid. Außerdem erfolgte im Rahmen der Arbeit die Synthese eines Materials nach IMANAKA et al. (Al0,8Zr0,8)4/3,8Nb(PO4)3, das einen Al3+-Ionenleiter darstellen soll, wobei die bisherigen Nachweise nicht eindeutig waren. Für die Sauerstoffaustauschmessung wurde ein gasdurchflossener Messstand entworfen, aufgebaut, evaluiert und für die beschriebenen Experimente eingesetzt. Dieser basiert auf coulometrischer Sauerstofftitration mittels kommerzieller Festelektrolytgassensoren. Diese werden potentiostatisch betrieben. Zusammen mit der entsprechenden Steuerung und dem gesamten Aufbau gelingt es auf diese Weise, im p(O2)-Bereich zwischen 25 mPa und 2,4 Pa die coulometrische Titration von Sauerstoff zu untersuchen, was mit bisherigen Aufbauten nicht möglich war. Der Messstand wurde mittels Sauerstoffpump-Experimenten hinsichtlich der Abhängigkeiten der Titrationseffizienz vom Volumenstrom bzw. der Sauerstofftitrationsausbeute vom p(O2) des Messgases untersucht. Es konnte gezeigt werden, dass es mit diesem Messstand machbar ist, mit hoher Effizienz Sauerstoff zu titrieren. Mithilfe von elektrochemischer Pulspolarisation einer 8 mol-% YSZ-Probe wurden dann kleinste Sauerstoffmengen im Probenofen freigesetzt und so die untere Nachweis- und Bestimmungsgrenze des Aufbaus im p(O2)-Bereich zwischen 25 und 310m Pa von 10 pmol bzw. 35 pmol bestimmt. Des Weiteren wurde gezeigt, dass sich neben elektrochemisch induziertem auch thermisch induzierter Sauerstoffaustausch detektieren lässt und so damit in-operando-Untersuchungen an z.B. Gassensoren durchgeführt werden können. Um die Aluminiumionen-Leitfähigkeit des synthetisierten Materials untersuchen zu können, wurde im zweiten Teil der Arbeit ein Messstand zur Hochtemperatur-Tubandt-Messung konzipiert, aufgebaut und seine Funktionsfähigkeit mit der Silberionenleitung in AgI geprüft. Mit den Untersuchungen am potentiellen Aluminiumionenleiter konnte eine solche Ionenleitung bei Temperaturen von bis zu 600 °C sowohl in N2 als auch in reduzierenden Gasgemischen aus H2 und N2 nicht nachgewiesen werden. Neben der Untersuchung des Sauerstoffaustauschs im beschriebenen Aufbau wurde dieser auch genutzt, um unter kontrollierten Bedingungen (Temperatur, p(O2)) Impedanzmessungen durchzuführen und somit einen Zugang zu den elektrischen Eigenschaften der Proben zu erhalten. Die Art und Weise der Auswertung der erhaltenen Impedanzdaten ist dabei entscheidend für die Ermittlung der stoffspezifischen Parameter der Probe. Deshalb beschäftigte sich der letzte Abschnitt der Dissertation mit einem Fitting-Verfahren zur Bestimmung der materialspezifischen Parameter auf Basis von einfachen komplexen Gleichungen. Auf Basis des sogenannten Brick-Layer-Modells (BLM) wurden analytische komplexe Gleichungen hergeleitet, die eine möglichst einfache Beschreibung der Impedanz einer aus einem Material gesinterten Probe darstellen, die aus Körnern und Korngrenzen besteht. Das BLM beschreibt das Korn als einen Würfel, der von der Korngrenze auf seinem Mantel umhüllt wird. Die Gleichungen beschreiben das Impedanzverhalten mit den 5 Materialparametern (Leitfähigkeit und relative Permittivität von Korn und Korngrenze und Größenverhältnis zwischen Korngrenzendicke und Korngröße) und der Frequenz. Zur Evaluierung wurden Finite-Elemente-Simulationen genutzt, um Impedanzdaten mit bekannten Materialparametern zu erhalten und es wurde ein Fitting-Verfahren entwickelt, das die Extraktion dieser Parameter aus den Impedanzdaten erlaubt. Voraussetzung dafür ist, dass einer der fünf Materialparameter bekannt ist. Die Ergebnisse zeigen, dass dieses Verfahren eingesetzt werden kann, um Proben mit Korngrößen zwischen wenigen Nanometern und mehreren Mikrometern zu analysieren. Dies wird an einer Impedanzmessung einer YSZ-Probe verdeutlicht.:1 Einleitung 1 2 Grundlagen 3 2.1 Feste Elektrolyte 3 2.1.1 Leitungsprinzipien 4 2.1.2 YSZ 5 2.1.3 Aluminiumionenleiter 8 2.1.4 GDC/MgO-Nanokomposite 10 2.2 SnO2 11 2.3 Sauerstoffaustauschmessungen mittels Festelektrolytgassensoren 13 2.3.1 YSZ-basierte Festelektrolytgassensoren 13 2.3.2 Stand der Technik zur Sauerstoffaustauschmessung 16 2.3.3 Forschungsbedarf 18 2.4 Impedanzspektroskopie 19 2.4.1 Impedanzspektroskopie an Elektrokeramiken 20 2.4.2 Forschungsbedarf 24 2.5 TUBANDT-Methode 25 3 Materialien und Methoden 27 3.1 Verwendete Chemikalien 27 3.2 Präparation der untersuchten Proben 27 3.2.1 YSZ 27 3.2.2 Potentieller Aluminiumionenleiter 28 3.2.3 GDC/MgO-Nanokomposit 28 3.2.4 SnO2 29 3.3 Strukturelle Charakterisierung 29 3.3.1 Röntgenpulverdiffraktometrie (XRD) 29 3.3.2 Rasterelektronenmikroskopie (REM) 29 3.3.3 EDX-Mapping und hochauflösende Transmissionselektronenmikroskopie (HRTEM) 29 3.4 Elektrochemische Charakterisierung 30 3.4.1 Impedanzspektroskopie 30 3.4.2 Messstand zur hochsensitiven coulometrischen Sauerstofftitration 30 3.4.3 Messstand zur Untersuchung der ionischen Leitfähigkeit nach TUBANDT 37 3.5 Modellierung und Fitten von Impedanzdaten 38 3.5.1 Finite-Elemente-Methode 38 3.5.2 FEM-Simulation des Impedanzverhaltens nach dem Brick-Layer-Modell 38 4 Ergebnisse und Diskussion 43 4.1 Ergebnisse zur Synthese nach IMANAKA 43 4.2 Coulometrische Sauerstofftitration 49 4.2.1 Messstand zur hochsensitiven Sauerstoffaustauschmessung 49 4.2.2 Charakterisierung des Aufbaus 52 4.2.3 Sauerstoffaustauschexperimente 69 4.3 Impedimetrische Messungen bei kontrollierten Bedingungen 79 4.3.1 Untersuchungen am potentiellen Aluminiumionenleiter 79 4.3.2 Untersuchungen am GDC-MgO-Kompositmaterial 82 4.4 Untersuchung der Ionenleitfähigkeit nach TUBANDT 83 4.4.1 Aufbau 84 4.4.2 Messungen an AgI 86 4.4.3 Messungen an synthetisiertem Material 87 4.5 Bestimmung materialspezifischer Parameter aus Impedanz-Spektren 89 4.5.1 Herleitung der analytischen Gleichungen 91 4.5.2 Verfahren zum Fitten von EIS-Daten mittels der analytischen Gleichungen 98 4.5.3 Fitten an künstliche Impedanz-Daten 103 4.5.4 Fitten an experimentelle Impedanz-Daten 112 4.5.5 Zusammenfassung der Ergebnisse 119 4.5.6 Ausblick 120 5 Zusammenfassung und Ausblick 121 A Anhang 127 Literaturverzeichnis 133

The aim of this thesis was development and initial testing of new porous electrochemical detector for flow-through arrangements, especially for flow injection analysis (FIA) and liquid chromatography. One of the most advantageous properties of the detector is simple renewal of working material and thus its suitability for determination of strongly passivating substances. Glassy carbon microbeads and copper microparticles were tested as a working material within this study. Initially, basic electrochemical properties of the glassy carbon-based detector were examined by FIA using hydroquinone and potassium ferrocyanide as model substances. For both model substances high degree of conversion was achieved (around 100 %), and thus it was concluded that glassy carbon-based detector can be considered as coulometric. Hereafter, practical application of the carbon-based detector are presented on five electrochemically active substances closely related to the human medicine and pharmacy - thymol, tyrosine, sulfamethizole and vanillylmandelic acid (VMA) simultaneously determinined with homovanillic acid (HVA). Complexity of instrumental arrangement of flow-through methods had been increasing consecutively up to the HPLC determination with gradient programme. It was proved that the carbon-based detector is...

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