No description available.

El selenio es un elemento considerado esencial y a la vez tóxico para el organismo humano. Para establecer una correlación con la biodisponibilidad del elemento in vivo, se pueden emplear diversos métodos de bioaccesibilidad in vitro que simulen condiciones de digestión. De entre los métodos in vitro utilizados en la literatura, el método Physiologically Based Extraction Test (PBET) es uno de los métodos más sencillos y más ampliamente utilizado. La mayor parte del presente trabajo ha tratado sobre los estudios de bioaccesibilidad de selenio basados en el consumo de vegetales comestibles. Para determinar el contenido de Se en los vegetales, se diseñaron diferentes sistemas de crecimiento con condiciones controladas. En este estudio, las plantas comestibles (3 tipos de brotes y 9 tipos de vegetales) se cultivaron en dos medios suplementados (hidropónico y turba, respectivamente) para obtener plantas con un contenido de Se similar a aquéllas que crecen en zonas con una concentración de Se elevada. Para ello, se utilizaron suplementos de sales solubles de Se y el aditivo Selcote Ultra ®. Otra parte del estudio ha sido sobre la bioaccesibilidad de selenio en suelos. En el presente estudio los suelos analizados fueron procedentes del suroeste de los Estados Unidos y su contenido natural fue de 6,8 ± 0,1 mg kg - 1 y 7,6 ± 0,2 mg kg - 1. Durante el presente estudio, el contenido total de selenio y la concentración de las especies de selenio se determinaron en los diferentes materiales utilizando diversas técnicas y procedimientos. Respecto al medio hidropónico, se comprobó que el Se (VI) era más fácilmente absorbido por las plantas que la especie de Se (IV). Respecto a la determinación de Se total se observó que todos los vegetales estudiados absorbieron más cantidad de selenio a medida que aumentaba la concentración de este elemento en el medio fortificado con sales solubles, apareciendo síntomas de deterioro y de inhibición del crecimiento de los vegetales con las fortificaciones de selenio más elevadas. También se observó que las plantas crecidas en presencia del aditivo Selcote Ultra® absorbieron más lentamente el selenio presente en la turba, que las plantas crecidas con sales solubles de selenio. El selenio inorgánico absorbido por las plantas fue transformado principalmente en SeMet, excepto para las plantas del género Allium que contenían principalmente la especie γ-glutamil-Se-MeSeCys. Con respecto al trabajo experimental llevado a cabo durante la estancia de investigación en el Laboratorio de Química Analítica, Bio-Inorgánica y Medio Ambiente (LCABIE), de la Université de Pau et des Pays de l’Adour, se trabajó con diferentes técnicas y procedimientos y se consiguió ampliar la información obtenida con respecto a la especiación de Se. El método PBET se utilizó para estudiar la fracción bioaccesible de Se en suelos y plantas. Mediante la extracción PBET se comprobó que, para los suelos estudiados, la fracción considerada como bioaccesible fue atribuida principalmente a la etapa gastrointestinal del método PBET y correspondió al 50% de Se, incluyendo las especies de Se (IV) y Se (VI). Además, el método PBET de las especies de Se presentes en suelos, se equiparó a una extracción simple con ácido fosfórico. Respecto a los vegetales analizados (col y ajo), se consiguieron extraer las especies de selenio predominantes: selenometionina y γ-glutamil-Se-MeSeCys. También se observó que un porcentaje de este segundo selenocompuesto se degrada a Se-MeSeCys debido a la acción enzimática. En el caso de los vegetales, también se estudió el efecto de diferentes tratamientos aplicados previamente al método PBET (como el proceso de cocción). Se observó que el tratamiento de cocción de las muestras de col favoreció el incremento de la concentración de la especie selenometionina y redujo la concentración de Se (VI) en los extractos gastrointestinales del método PBET, debido a que un gran porcentaje de Se inorgánico se extrajo previamente en el proceso de cocción. Finalmente se han puesto de manifiesto los resultados más importantes obtenidos en el presente estudio y se han comparado con los datos encontrados en la literatura. / Selenium is considered both an essential and toxic element for the human health. Therefore, it is of great interest to study the presence and bioavailability of the selenocompounds in foods and the possible toxic effects from the ingestion of contaminated materials, which depend on their absorption and metabolism. Therefore, given the effects that different Se species can have in the organism, it is necessary to establish a method to study the bioaccessibility of this element, as a step prior to determining bioavailability. Among the in vitro methods used in the literature, the Physiologically Based Extracted Test (PBET) seems to be the easiest and most widely used method. A broader part of this study concerned Se bioaccessibility based on plant consumption. To determine the Se content in plants, different growth systems involving controlled conditions were designed. In this study, the edible plants (3 kinds of sprouts and 9 kinds of vegetables) were grown in two media supplemented (hydroponic and peat, respectively) to obtain plants with a natural Se content similar to those growing in areas with a high Se concentration. Another part of the study was about the Se bioaccessibility in soils. Little information is known about this topic, since most studies on bioaccessibility have concerned heavy metals (such as Pb, Cd, or Cr). In the present study the soils analyzed were obtained from the southwestern United States with Se natural content. During the present study, the total Se content and the concentration of the Se species were determined in the different materials using various techniques and procedures. The PBET method was then used to study the bioavailable fraction of Se in soils and plants. Finally, we highlighted the most important results obtained in the present study and we compared our results with data found in the literature.

For biosensing applications it is often desirable to immobilise biomolecules securely on the electrode surface. The research described here was performed to develop and characterise modified conducting polymers suitable for use in the development of biosensor arrays. The research pursued centred around a post polymer-deposition modification strategy based on nucleophilic substitution of the pentafluorophenol group of the polymerised pyrrole derivative, pentafluorophenyl 3-(pyrrol-1-yl) propanoate (PFP). The activated ester present within this derivative is as an ideal reaction site for amine terminated species. Initially, electrochemical polymerisation growth conditions were determined and controlled to produce homopolymer and copolymer films with different structural and electrochemical characteristics. These polymer films were subsequently modified through various chemical reactions (e.g. with biotinylated species) to produce templates that could be used to biosensor developments. Furthermore, an important aspect in the development of a biosensing interface is the minimisation of non-specific adsorption and to that end a strategy was developed that involved modifying poly(PFP) films with poly(propyleneglycol) motifs. Usefully, an XPS based technique was developed to determine the extent of adsorption of labelled biological macromolecules on the modified poly(PFP) surfaces. Significantly, towards the development of a multianalyte biosensing substrate, a method was developed to control the reaction of solution based amine terminated species with the homopolymer poly(PFP). This involved electrochemically doping the polymer film to inhibit/promote nucleophilic reaction with amine containing species. Preliminary examples are given of the application of this technique was to micropattern species on multi-digitated electrodes.

This thesis presents work on the development of a number of scanned electrochemical probe microscopies. Such techniques have widespread applications, from materials science to the life sciences. Advances in flexible instrumentation, coupled with the theoretical description of electrochemical systems, are central themes which allowed for the fruitful investigation of a variety of experimental systems. Theoretical descriptions of scanning ion conductance microscopy (SICM) were developed, particularly to investigate the effect of tip-geometry on imaging resolution. This technique has already found a number of applications in the life sciences, but image resolution has not previously been addressed adequately. Images were recorded showing tip-convolution that were in agreement with theoretical predictions. The scanning microcapillary contact method (SMCM) was developed, as a method of assessing spatial heterogeneities in electrode activity on the submicron length-scale. An electrolyte filled microcapillary containing a reference/auxiliary electrode was approached to a substrate (working) electrode surface, via piezoelectric positioners. Contact of the electrolyte meniscus with the substrate electrode was sensed by a current flowing. Electrochemical measurements were performed before the microcapillary was retracted and another point on the sample was characterised. Spatial heterogeneities in electrode activity were imaged on a sub-micron length-scale and the activity of basal plane highly oriented pyrolytic graphite (HOPG) was demonstrated. Tip position modulation scanning electrochemical microscopy (SECM-TPM), where an ultramicroelectrode (UME) is oscillated perpendicularly to a surface and an amperometric current is recorded, was investigated experimentally and theoretically. A model including convective mass-transport was developed that gave an accurate description of the experimental situation. It was demonstrated that SECM-TPM is a potentially powerful approach for the measurement of the permeability of a sample. SECM experiments were performed investigating the growth of Ag particles at a liquid/liquid interface, which was caused through the electrodissolution of a Ag UME in an aqueous phase, and the reduction of the Ag+ ion by an electron donor in the organic phase. A model was created that allowed for the interpretation of data. Cyclic voltammetry investigations of HOPG covered with a Nafion film containing a redox mediator confirmed the activity of basal plane HOPG, as demonstrated by SMCM measurements. Nafion slowed diffusion sufficiently to allow the spatial-decoupling of surface sites with different activity.

No description available.

No description available.

This thesis presents work undertaken using Synchrotron and Laboratory based techniques in parallel on the Chemical State and Luminescence Imaging of Natural and Synthetic Diamond. X-ray absorption spectroscopy (XAS) techniques have revealed information on the chemical structure and bonding within brown and variegated type Ia, IIa, CVD and high-pressure, high-temperature (HPHT) treated diamonds. XAS, Raman, X-ray Excited Optical Luminescence (XEOL) and Photoluminescence (PL) are some of the techniques that have been applied to characterise and investigate the cause of the brown colouration. The XAS measurements have been undertaken in imaging mode with the capabilities of correlating the luminescence image with the brown regions in partial luminescence yield (PLY) and total luminescence yield (TLY). OD-XAS spectrums have been obtained at non-brown and brown regions and have revealed a higher concentration of sp2-bonded carbon present at the brown sites. Raman spectroscopy utilized in imaging mode also supports this discovery.

The formation of potentially harmful trihalomethanes (THM) when using chlorine as a disinfectant in potable water supplies has led to tighter regulatory controls and hence a need for better models for THM management. The prediction of THM concentration is difficult due to the complex and changing hydrodynamic and chemical regimes found in water treatment works (WTWs) and distribution systems. The purpose of the study is to increase understanding of THM formation and chlorine decay through six water treatment works (WTWs) and distribution systems operated by Severn Trent Water Ltd and ultimately develop an efficient, robust, cost effective model for chlorine decay and THM formation. With knowledge of the bulk chlorine decay characteristics and the THM productivity of the water, this model offers a simple and straightforward tool which can be readily applied to WTWs and distribution systems alike to provide an initial assessment of the risks of total THM formation at different sites, and to identify sites and systems at risk of compliance failure. Relying only on the measurement of analytically undemanding parameters (in particular, chlorine and its decay with time), under appropriate circumstances this model offers advantages of simplicity and cost-effectiveness over other, more complex models. The model can thus be applied to assess the chemical risk under different scenarios allowing for informed decision making.

Ambient mass spectrometry (AMS) is a new and versatile method for analysing a multitude of different sample types with the benefit of analysis at ambient pressure and the many other advantages that this entails. However, as these techniques are still in their infancy, metrological development of the techniques is essential. This is a critical step before AMS can be used reliably in the application areas in which it has shown great promise. The research in this thesis addresses the development of AMS sources, in particular plasma-assisted desorption-ionisation, PADI. Optimisation and characterisation is fundamental to understanding and developing the technique. Optimisation of PADI is addressed; this includes understanding the effects of different parameters to maximise signal intensities. The power, and temperature, of the plasma is shown to have a significant effect on the fragmentation observed in the mass spectra. This is an important result that is further explored with the use of thermal desorption to aid the analysis of low volatility molecules. The form of the analyte is also an important consideration for analysis by PADI; characteristic ions from powders are easily detected, whereas for thin film samples an analyte vapour pressure of greater than 10-4 Pa is needed. This result provides an indication of the limitations of PADI and what classes of analyte it will be successful at analysing. It is also shown that we can improve signal intensities using a heated sample stage allowing the analytes to be thermally desorbed before being ionised by the plasma. This is an important result for future work, where ambient plasma sources can be implemented as an ionisation source in conjunction with another mechanism, such as thermal or laser desorption, to generate gas-phase ions. A comparison of different ambient methods for personal care products shows the usefulness and also complementarities of PADI with desorption electrospray ionisation, DESI, one of the most established AMS techniques which utilises a different mechanism for desorption and ionisation. This also demonstrates the chemical information that can quickly be gained from these techniques, with minimal sample preparation. DESI is also compared to secondary ion mass spectrometry, SIMS. Vacuum-based techniques such as SIMS are much more established than ambient techniques; it is insightful to understand the advantages that each source can offer, for the analysis of different types of molecule as well as the mass spectral information that can be gained from SIMS and DESI.

Im Rahmen dieser Arbeit wurden sehr einfache, flüssigchromatographische Methoden zur Qualitätsanalytik gebräuchlicher Antimalaria-Medikamente (Amodiaquin, Mefloquin, Proguanil sowie die Kombination Artemether/Lumefantrin) entwickelt, die nur wenige, günstig erhältliche Chemikalien (Phosphatpuffer, Methanol) sowie gewöhnliche, kommerzielle RP-18-Säulen benötigen. Sie sind insbesondere zur Anwendung in Laboratorien in Entwicklungsländern geeignet und erfordern keine komplexen HPLC-Instrumente wie beispielsweise Gradientenpumpen oder Säulenthermostate. Der Verzicht auf Ionenpaarreagenzien ermöglicht es, dass eine stationäre Phase für mehr als nur einen einzigen Einsatzzweck verwendet werden kann und dass langwierige Äquilibrier- bzw. Spülschritte nicht notwendig sind. Alle Methoden arbeiten im isokratischen Elutionsmodus und durch die Verwendung kurzer Säulen (125 mm) konnten die jeweiligen Analysenzeiten zusätzlich verringert werden. Hierdurch ist zudem eine Reduzierung des Fließmittelverbrauches möglich. Während der Methodenentwicklung wurden charakteristische, aus dem Herstellungsweg des jeweiligen Arzneistoffes stammende potentielle Verunreinigungen berücksichtigt. Ihre Bestimmung erlaubt eine Aussage über die Herkunft eines Wirkstoffes bzw. eines Arzneimittels, da das Verunreinigungsmuster einer Substanz oftmals die Zuordnung zu einem bestimmten Herstellungs- bzw. Reinigungsprozess ermöglicht. Alle Methoden wurden hinsichtlich der Linearität innerhalb des Arbeitsbereiches sowie der Wiederholpräzision charakterisiert. Es wurde eine gute Reproduzierbarkeit gefunden. Die Nachweis- und Bestimmungsgrenzen der untersuchten Verunreinigungen lagen bei einem Level von je 0.1 %. Durch gezielte Variation wurde der Einfluss wechselnder Trenntemperaturen sowie schwankender pH-Werte der jeweiligen mobilen Phase und die hieraus resultierenden Effekte untersucht. Hierbei zeigte sich, dass die Methoden sehr robust gegenüber diesen Einflussgrößen sind und somit für die Anwendung mit einfach ausgestatteten HPLC-Systemen sowie besonders für den Einsatz in tropische Gebieten mit wechselnden klimatischen Bedingungen gut geeignet sind. Flüssigchromatographische Methoden spielen heute in der pharmazeutischen Analytik vor allem zur Bestimmung der Reinheit eines Arzneistoffes eine herausragende Rolle und sind in nahezu jeder Monographie der wichtigsten Arzneibücher (z. B. im Ph. Eur.) zu finden. Einfach durch-führbare Untersuchungsmethoden, wie beispielsweise die im GPHF-Minilab® angewandte Dünnschichtchromatographie, erfordern im Vergleich zur HPLC weniger komplexe und teure Instrumente und können selbst in entlegenen Gebieten ohne Laboratorium durchführt werden. Sie verfügen allerdings über eine nur sehr geringe Genauigkeit und Reproduzierbarkeit, da sowohl die praktische Durchführung als auch die anschließende Auswertung rein manuell bzw. visuell erfolgt und somit in hohem Maße einer Beeinflussung durch den jeweiligen Analytiker unterworfen ist. Die entwickelten HPLC-Methoden wurden mit dünnschichtchromatographischen Verfahren verglichen, hierbei besonders unter dem Aspekt der visuellen und der instrumentellen Auswertung der Chromatogramme zur Bestimmung des Gehaltes einer unbekannten Probe. Hierbei konnte aufgezeigt werden, dass die Dünnschichtchromatographie der Flüssigchromatographie eindeutig unterlegen ist, insbesondere wenn die Auswertung nicht mittels eines entsprechenden Scanners sondern rein visuell erfolgt: Nur in den wenigsten Fällen ist es möglich, eine annähernd präzise Aussage über den Gehalt zu treffen und zudem ist die Bestimmung der Verwandten Substanzen nur sehr bedingt möglich. Durch den Einsatz von Auftragegeräten bzw. Plattenscannern kann die Genauigkeit zwar signifikant erhöht werden, allerdings sind solche Instrumente im Verhältnis wesentlich teurer als einfache, modulare HPLC-Systeme und zählen heute in den wenigsten Laboratorien zum Standardinventar. Vereinfachte chromatographische Methoden können ein wichtiges Hilfsmittel für Kontrolllaboratorien in Entwicklungsländern sein, wenn komplexe, etablierte Protokolle nur eingeschränkt angewendet werden können. Durch die Kombination aus dünnschichtchromatographischer Basisanalytik und einer flächendeckenden Untersuchung mittels HPLC lässt sich die Arzneimittelqualität sehr gut überprüfen, die regulatorischen Organe eines Landes entsprechend zu entlasten und die Versorgung der Bevölkerung mit qualitativ einwandfreien Medikamenten zu gewährleisten. Ein weiterer Teil der Arbeit befasst sich mit der Stabilitätsanalytik individuell hergestellter, Noradrenalin-haltiger Injektionslösungen. Solche Rezepturen werden oftmals in Krankenhausapotheken im Rahmen der Defektur auf Vorrat durch Verdünnen der entsprechenden kommerzieller Fertigarzneimittel mit isotonischer Kochsalzlösung zubereitet, um z. B. für Notfallsituationen am Wochenende die Rezepturen vorrätig zu haben. Durch die Untersuchungen wurde geprüft, inwieweit der übliche Verdünnungsgrad von 0.1 % einen Einfluss auf die Stabilität des Noradrenalins hat und welche Lagerungsbedingungen für die Zubereitungen empfohlen werden können. Nach der Lagerung unter verschiedenen Bedingungen (gekühlt, bei Raumtemperatur sowie jeweils mit bzw. ohne Lichtschutz) konnte gezeigt werden, dass die Gehalte an Noradrenalin bei keiner der untersuchten Lagerungsbedingungen unter einen Wert von 99.0 % fielen. Individuell hergestellte Noradrenalin-Injektionslösungen können somit bis zu sieben Tage im Voraus hergestellt und für die Anwendung am Patienten bereit gehalten werden. Die Lösungen sollten dennoch gekühlt und unter Lichtschutz aufbewahrt werden, um den Abbau des Arzneistoffes und eine mikrobielle Kontamination zu minimieren. / This work focuses on the development of simple, liquid chromatographic methods for the quality analysis of common antimalarial medicines, i.e. amodiaquine, mefloquine, proguanil and the fix-dose combination of artemether and lumefantrine. They require a minimum of readily available, cheap chemicals (e.g. phosphate buffers or methanol) and commercially available RP-18 columns. They were designed for use in quality control laboratories in resource-restraint environments, e.g. in laboratories in the developing world, and do not require complex HPLC instrumentation which are either not available or affordable, e.g. with expensive gradient pumps or column ovens. Ion-pairing reagents were strictly avoided during method development which is a great advantage for routine application: long equilibration and flushing procedures are not necessary and a column can be used for more than one single method. An isocratic elution mode was applied and using short analytical columns (125 mm) allows reducing the analysis time and eluent consumption, respectively, to a minimum. During method development impurities being characteristic for the respective synthesis pathway(s) of the active substances were considered. Thus, determining the quality of a com-pound with regard to its content and purity is possible and distinct manufacturers or sources can be identified. Linearity and repeatability were assessed and a good reproducibility was found. Limits of detection and quantitation, respectively, were measured and the respective impurities can be determined to a level of 0.1 %. By varying the separation temperature and the pH-value of the respective mobile phases method ruggedness was investigated. A high grade of robustness towards these parameters could be confirmed, indicating that the methods are suitable for being used in tropical environments. Liquid chromatographic methods play an important role in pharmaceutical analysis today and they are widely applied for determining the purity of a compound. Respective protocols have been added to almost every monograph of the most important pharmacopoeias, e.g. the European Pharmacopoeia. Of note, those protocols may not be applied in every laboratory without limitations. Although very simple methods of analysis, e.g. thin-layer chromatography which is described in the manuals of the GPHF-Minilab®, require less expensive instruments and may even be applied in resource-restraint environments, they exhibit a poor accuracy and reproducibility. Preparing and evaluating the plates manually may strongly bias the results, and in addition this highly depends from the respective analyst who performs the tests. The comparison of thin-layer chromatographic assays applying a manual and an instrumental evaluation to results obtained from liquid chromatographic tests clearly exhibited the disadvantages particularly for determining the quality of a compound. It is almost impossible to exactly determine the content of a sample, and a comprehensive test for related substances cannot be carried out. Using application devices and plate readers may increase the accuracy, however such instruments are a lot more expensive than simple, modular HPLC systems and normally do not belong to the standard inventory of a quality control laboratory. Simplified HPLC methods may serve as helpful instruments for the regulatory infrastructure of developing countries. Combining them with basic thin-layer chromatographic tests and applying them comprehensively may enable the respective quality control laboratories to ensure the nationwide supply with immaculate medicines. In the second part of this work the stability of individually prepared dilutions of commercially available norepinephrine injectable solutions was investigated and recommendations for storage conditions were derived. In hospital pharmacies it is a common practice to prepare such solutions from proprietary products by diluting them with isotonic sodium chloride solution or other suitable buffer solutions, respectively, to a concentration of 0.01 mg/ml (1:100). This is important particularly in case of emergencies, e.g. on the weekend or during holidays, because the respective medication can be held in stock even when the pharmacy is closed. Within the framework of the experiments the influence on the stability of norepinephrine after diluting the respective proprietary product with sodium chloride solution was investigated. The samples were stored with and without refrigeration, and unprotected and protected from sunlight. The results showed that under none of the investigated storing conditions the content of norepineprhine decreased significantly. The lowest content which was found was 99.0 %. Thus, individual norepinephrine injectable solutions can be prepared in advance and storing them is possible for at least seven days. Although a degradation of the active ingredient or a diffusion in the primary packaging material (e.g. a syringe made from polyethylene) could not be observed, it is recommended to store the preparations in the refrigerator and protected from light. A microbial contamination may also be avoided like this.