The determination of the isotopic composition of single uranium oxide particles, size 0.3-2 μm, for nuclear safeguards is current performed by either thermal ionisation mass spectrometry (TIMS) or Secondary Ion Mass Spectrometry (SIMS). Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), a well-established analytical technique for determining the isotopic composition of solid materials, has the potential to be another method by which single uranium oxide particles can be analysed, complementing established protocol, but requires optimisation. In this study the ability of LA-ICP-MS to determine the isotopic composition, principally 234U/238U, 235U/238U and 236U/238U, of glass reference materials and sub-micron uranium oxide particles is investigated. To achieve the best detection efficiency a prototype high-speed ablation cell and injector design, designed previously at Loughborough University, was coupled to a high efficiency multi collector (MC-) ICP-MS. As a result an increase in signal-to-noise ratio and a measured detection efficiency of 5-7% was achieved for a LA-MC-ICP-MS system. The capability of the LA-MC-ICP-MS system, for the determination of the uranium isotopic composition of single particles was compared to a more established low-volume ablation cell. A source of additional uncertainty, blind time arising from incompatibilities with the mixed detector array of the MC-ICP-MS was identified. The impact of the additional uncertainty on isotope ratio analysis was modeled and a method developed to filter out affected data. LA-ICP-MS and LA-MC-ICP-MS were used to successfully determine the uranium isotopic compositions of sub-micron uranium oxide particles, of a known certified composition. A sample planchet containing particles of two distinct isotopic compositions was resolved. The utility of three data evaluation strategies to determine the isotopic composition of single uranium oxide particles was investigated. The necessity and advantages of calculating isotope ratios using the geometric mean is demonstrated, which has application for isotope ratio analysis performed on all forms of mass spectrometry. A novel approach to prepare particulate samples for laser ablation analysis, cytocentrifugation, is described. By using as the solvent, a mixture of nail polish and acetone, dispersed particles are held in a strong film layer thin enough to allow embedded particles to be imaged by SEM-EDX. A sample of uranium oxide particles in an environmental matrix prepared using cytocentrifugation is analysed by LA-MC-ICP-MS and their isotopic composition resolved.

Studies of the interaction of the relevant metal, metalloid or nanoparticulate species with biological systems are underpinned by the provision of reliable information about chemical composition of the relevant materials. Often, no methods of chemical analysis are available. The work described in this dissertation centers on developing methods to help with studies for a variety of analytes and samples. A method was developed for the determination of 11 trace elements (As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Pb, Ti, and Zn) in human breast milk and infant formulas by inductively coupled plasma optical emission spectrometry (ICP-OES) following microwave-assisted digestion. A method was established for the determination of trace elements, with an emphasis on titanium as titanium dioxide, in snack foods and consumer products. The interactions of some dissolved metals, including rare earth elements, and metallo-nanoparticles (silver, gold, titanium dioxide, aluminum oxide, and iron) with aquatic plants were studied. After exposure in a variety of mesocosms, the partitioning of the elemental species between various compartments was quantified by ICP-MS and ICP-OES following microwave-assisted digestion. An ICP mass spectrometry (MS) method has also been developed to quantify the uptake of gold and silver nanoparticles by C. elegans. Uptake of gold nanoparticles was size dependent, suggesting increased ingestion efficiency with increased particle diameter. The feasibility of discriminating between suspended TiO2 nanoparticles and dissolved titanium by the analysis of the rapid transient signal events obtained from the ICP-MS instrument operated in a rapid response mode was also developed. Data handling parameters were established that allowed a distinction in the signals for nanoparticulate and standard solutions. Spikes in the signal were defined by distinct parameters using the mean and standard deviation, where a spike in the signal was defined as a signal > + ks (k =3). This approach however did lead to a statistical difference in the spike signal events for solutions and nanosuspensions.

Les nanoparticules d’argent (Ag NPs) sont considérablement utilisées dans l’industrie alimentaire. Elles sont fortement appliquées comme enrobages d’emballages alimentaires afin d’assurer une meilleure qualité des aliments et une plus longue durée de conservation sur les étagères des supermarchés. En revanche, les risques associés aux Ag NPs sont inquiétants. Leurs effets potentiels sur les humains et sur l’environnement suscitent un grand intérêt scientifique. C’est pourquoi il est important de valider des méthodes analytiques pour détecter, caractériser et quantifier les Ag NPs dans la nourriture mise en contact avec ce type de contenant. Les méthodes permettront de mieux comprendre la migration de l'argent vers les aliments directement ingérés par l’humain. La spectrométrie de masse à plasma à couplage inductif en mode particule unique (SP-ICP-MS) est une technique prometteuse pour caractériser et quantifier de petites particules (de quelques nanomètres) à de faibles concentrations (dans l'ordre du ng L-1). Contrairement aux techniques analytiques conventionnelles, telles que les techniques de microscopie et de diffusion de la lumière, le SP-ICP-MS distingue la forme ionique de la forme particulaire de l'analyte. Cette présente étude valide une méthode pour la caractérisation et la quantification des Ag NPs et de l’argent ionique dans deux boissons et trois simulants: jus d'orange, préparation en poudre pour nourrissons, eau Milli-Q, acide acétique à 3% et éthanol à 10%. De plus, une meilleure compréhension du devenir et de la migration de l’argent provenant d'emballages alimentaires nano-activés a pu être obtenue. En effet, les milieux acides et les traitements thermiques ont engendré de plus grands relargages d’argent, sous forme ionique, contrairement aux milieux dits « lipophiles » tels que la préparation pour nourrissons et l’éthanol. En conclusion, ce mémoire nous démontre que les voies de libération des NPs des contenants nano-activés ne sont pas encore très bien comprises. De plus amples études doivent être entreprises afin de pouvoir établir des modèles de migration clairs et afin de mieux comprendre les risques associés à leurs utilisations. / Silver nanoparticles (Ag NPs) are increasingly used in the food industry. They are integrated into coatings of various food packaging to help ensure longer product shelf life. However, the risks associated with Ag NPs are currently not well known and their potential effects on humans are causing growing concern. Furthermore, it is not clear whether NPs have greater or lesser risk than dissolved silver ions or bulk phase Ag. Consequently, it is necessary to detect and to characterize the release of silver from silver-enhanced containers into real food matrices using sensitive analytical techniques that allow one to distinguish between silver ions and nanoparticles. Single particle ICP-MS is a promising technique to count and size small particles at low concentrations. Compared to other conventional instrumentation, it can distinguish between ionic and particulate forms of the analyte. This thesis focused firstly on the validation of an analytical method for the analysis of Ag NPs and ionic silver in three different food simulants (Milli-Q water, 10% ethanol and 3% acetic acid) and in two drinks (orange juice and infant milk formula). A better understanding of the aging and of the migration of silver has been reached in these matrices. Essentially, acidic media caused significant NP oxidation whereas organic macromolecules like lipids, proteins and polysaccharides appeared to increase the stability of the NPs. Subsequently, a migration study from silver-enhanced containers showed significant release of dissolved Ag in 3% acetic acid and a lower release in milk formula. Also, heating led to a considerable release of silver from the container. To conclude, further studies are needed to obtain clear release models to better understand the risk on humans and on the environment.

Im Rahmen dieser Arbeit wurden vier verschiedene Methoden zur Separation, Identifikation sowie Quantifizierung von Silber-Nanopartikeln (Ag-NP) entwickelt. Mittels asymmetrischer Fluss-Feldflussfraktionierung (AF4) in Kombination mit einem induktiv gekoppelten Plasma-Massenspektrometer (ICP-MS) konnten eine gute Trennung und hohe Wiederfindungsraten gefunden werden. Eine systematische Studie möglicher Probenverluste während der Methodenoptimierung zeigte, dass der größte Verlust durch die Ag+-Ionen verursacht wurde, während Verluste durch Ablagerungen auf der Membran vernachlässigbar waren. Für Citrat-stabilisierte Ag-NP konnten mittels Hohlfaser-Fluss-Feldflussfraktionierung (HF5) gute Trennergebnisse erreicht und der hydrodynamische Durchmesser bestimmt werden. Zur Bestimmung der Partikelanzahlgrößenverteilung und des geometrischen Durchmessers von Partikeln in unbekannter Matrix wurde die Isotopenverdünnungsanalyse (IVA) erfolgreich mit der Einzelpartikel ICP-MS kombiniert. Weiterhin wurde eine Hochdruckflüssigkeitschromatographie(HPLC)-IVA-ICP-MS-Methode entwickelt, mit welcher NP und ihre korrespondierenden Ionen getrennt und quantifiziert werden konnten. Ein Vergleich der Ansätze zeigt, dass eine Kombination mehrerer Methoden nötig ist, um alle relevanten Informationen über die NP zu erhalten. Zum Abschluss wurde mit den entwickelten Methoden das Umweltverhalten der Ag-NP in einer Huminsäure(HS)-Suspension untersucht. Hierbei wurden erste Stabilisierungseffekte in Bezug auf die Ag-Konzentration und Partikelanzahl festgestellt. Zudem konnte mittels HF5 und HPLC für kleine NP in HA eine Modifikation in Form der Ausbildung eines zweiten, kleineren NP-Signals beobachtet werden. / In this work, four different methods for the separation, identification, and quantification of silver nanoparticles (Ag-NP) were developed. Using asymmetric flow field-flow fractionation (AF4) in combination with inductively coupled plasma mass spectrometry (ICP-MS), a good separation and high recovery rates were found. A systematic investigation of possible sample losses during the method optimization showed that Ag+ ions caused the highest loss and only negligible amounts of Ag residues on the membrane were found. For citrate-stabilized Ag-NP, hollow fiber flow-field flow fractionation (HF5) analyses achieved good results for the separation and calculation of the hydrodynamic diameters. In order to determine the particle number size distribution and the geometric diameter for samples in unknown matrices, isotope dilution analysis (IVA) was successfully combined with single particle ICP-MS. Additionally, a high-performance liquid chromatography (HPLC)-IVA-ICP-MS approach was developed, which was able to separate and quantify NP and their corresponding ions. A comparison of the methods showed that a combination of different approaches is necessary to obtain all relevant information. Finally, the methods were applied to analyze the environmental behavior of Ag-NP in a humic acid (HS) suspension. Here, first stabilization effects in terms of the Ag concentration and particle number concentration were detected. Using HF5 and HPLC for the analysis of small NPs in HS, a modification in the form of a second, smaller NP signal was observed.

La caractérisation de nanomatériaux dans des matrices alimentaires et animales suscite un intérêt scientifique important afin d’évaluer les risques potentiels de l’exposition liés à l’utilisation grandissante des nanomatériaux par plusieurs industries, y compris un certain nombre d’applications agroalimentaires. Un facteur limitant à l’étude et la réglementation des nanomatériaux dans des matrices complexes telle que la nourriture est l’absence de méthodes standardisées pour l’extraction et l’analyse de nanoparticules, tout en évitant l’altération de certaines caractéristiques physicochimiques des nanoparticules. Les travaux présentés dans ce mémoire abordent l’optimisation de plusieurs approches de préparation d’échantillon (hydrolyse enzymatique et alcaline) pour l’extraction de nanoparticules d’Ag préalablement équilibrées dans une matrice de boeuf haché mi-maigre. Les nanoparticules extraites ont été analysées par spectrométrie de masse à plasma à couplage inductif en mode particule unique (SP-ICP-MS) permettant la mesure de leur taille et concentration, mais aussi de la concentration en métal dissous, le tout à de très faibles concentrations (de l’ordre du ng/L). La validation de l’analyse par SP-ICP-MS a été réalisée par évaluation de la répétabilité, de la détermination des limites de détection et par une investigation de l’influence du traitement de données sur l’interprétation des résultats. Les pertes de nanoparticules lors de la préparation des échantillons ont été minimisées par l’identification et l’optimisation de paramètres clés tels que la composition du médium d’extraction, l’utilisation d’ultrasons et de la manipulation de l’échantillon après dégradation de la matrice. Les meilleurs recouvrements ont été obtenus par hydrolyse alcaline de la matrice en utilisant de l’hydroxyde de tetramethylammonium (TMAH), mais les échantillons obtenus étaient moins stables et plus susceptibles aux altérations des propriétés physicochimiques des nanoparticules que pour la dégradation par hydrolyse enzymatique utilisant lipase et pancréatine de porc. / The regulation and characterization of nanomaterials in foods and animal matrices are of great interest due to the potential risks associated with their exposure and the increasing number of instances where they are used within the food industry. One factor limiting the scientifically rigorous regulation of nanoparticles in foods is the lack of standardized procedures for the extraction of nanoparticles (NP) from complex matrices, without alteration of their physico-chemical properties. To this end, two sample preparation approaches (enzymatic- and alkaline-based hydrolyses) were tested and optimized in order to extract 40 nm Ag NP, following their equilibration with a fatty ground beef matrix. Extracted NP were characterized using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), allowing the determination of NP size and concentrations and also dissolved metal concentrations at trace levels. Validation of the SP-ICP-MS analysis was achieved by an evaluation of the repeatability and accuracy and by a determination of the various detection limits. Finally, we also looked into the influence of data treatment on interpretation of the results. NP losses during the sample preparation were minimized by identifying and optimizing key parameters such as the composition of the extraction media, usage of ultrasonication or the handling of the sample after separation from the undigested matter, among other points. The alkaline approach using TMAH (tetramethylammonium hydroxide) was found to have the highest recoveries, however processed samples were found to be less stable and more prone to alteration of the Ag NP physicochemical characteristics than samples processed using an enzymatic digestion based upon pork pancreatin and lipase.