Knowledge about selenium content of foods containing selenium species is very important in terms of both nutrition and toxicity. Bioavailability of selenium species for human body is different from each other. Hence, speciation of selenium is more important than total selenium determination. In the selenium speciation study, chicken breast samples, selenium supplement tablets and egg samples were analyzed for their selenium contents. In chicken breast study, chickens were randomly categorized into three groups including the control group (25 chickens), inorganic selenium fed group (25 chickens) and organic selenium fed group (25 chickens). After the optimization of all the analytical parameters used throughout the study, selenomethionine, selenocystine, Se(IV) and Se(VI) were determined using Cation Exchange-HPLC-ICP-MS system. In selenium supplement tablet study, anion and cation exchange chromatographies were used to determine selenium species. Arsenic is known as toxic element, and toxicity of inorganic arsenic species, As(III) and As(V), is much higher than organic arsenic species like arsenobetaine and arsenosugars. Hence, speciation of arsenic species in any matrix related with human health is very important. In the arsenic speciation study, Cation Exchange-HPLC-ICP-MS and Cation Exchange-HPLC-ES-MS systems were used to determine arsenobetaine content of DORM-2, DORM-3 and DOLT-4 as CRMs. All of the parameters in extraction, separation and detection steps were optimized. Standard addition method was applied to samples to eliminate or minimize the matrix interference. Thiols play an important role in metabolism and cellular homeostasis. Hence, determination of thiol compounds in biological matrices has been of interest by scientists. In the thiol study, Reverse Phase-HPLC-ICP-MS and Reverse Phase-HPLC-ES-MS systems were used for the separation and detection of thiols. For the thiol determination, thiols containing &ndash / S-S- bond were reduced using dithiothreitol (DTT). Reduction efficiencies for species of interest were found to be around 100%. Reduced and free thiols were derivatized before introduction on the column by p-hydroxymercuribenzoate (PHMB) and then separated from each other by using a C8 column. In the real sample measurement, yeast samples were analyzed using HPLC-ES-MS system.

ABSTRACT ARSENIC SPECIATION IN FISH BY HPLC-ICP-MS &Ouml / ZCAN, Sefika Eroglu M.S., Department of Chemistry Supervisor: Prof. Dr. O. Yavuz ATAMAN September 2010, 103 pages Arsenic speciation in fish samples on the market was performed using isocratic elution with cation exchange column high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) detection. Total As concentrations were found by ICP-MS using samples digested by nitric acid-hydrogen peroxide solution using microwave oven digestion / the results were in the range of 1.15-12.6 &micro / g/g. Separation of organic arsenicals, namely arsenobetaine (AB), dimethylarsinic acid (DMA) and monomethylarsonic acid (MA), have been achieved in 12 minutes. Freeze-dried samples were extracted by deionized water with a shaker system / the concentrations of AB and DMA in the extract was then determined using HPLC-ICP-MS. The accuracy of the method for determining AB concentration was confirmed using certified reference material (CRM), DOLT 4 (dog fish liver) / for this CRM only preliminary data are available for AB. The arsenic compounds in 6 fish muscle samples were investigated. The predominant arsenic compound found in extracts was AB / the concentrations were in the range of 0.86-12.0 &micro / g/g. DMA concentration was 0.40&plusmn / 0.03 &micro / g/g in one of the samples / in the others it was below the limit of quantation (0.21 &micro / g/g).

This thesis describes studies on the analysis of arsenic (As) in human biological samples, mainly urine but also hair and fingernails using inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GF-AAS). The relationship between ethnicity and arsenic metabolism was investigated for the first time for a population in the United Kingdom. This investigation has been carried out through comparative analysis of arsenic in human urine, hair and fingernails in volunteers from three different ethnic groups (Whites, Asians and Somali Black-Africans) who are only exposed to background levels of arsenic. Results obtained with 63 volunteers showed ethnic differences in urinary arsenic excretion as well as differences in arsenic levels in fingernail samples. The averages of total arsenic levels for the Somali Black-Africans (urine 7.2 µg/g creatinine; fingernails 723 µg/kg) are significantly (P< 0.05) different from both the Asians (urine 20.6 µg/g creatinine; fingernails 153.9 µg/kg) and Whites (urine 24.5 µg/g creatinine; fingernails 177.0 µg/kg). The Somali group also shows a higher percentage (50%) of dimethylarsinate (DMA) and a lower percentage (48%) of arsenobetaine (AB), compared to Asians (16% DMA and 83% AB) and Whites (22% DMA and 77% AB). The effect of fasting on urinary arsenic species distribution was also investigated by monitoring urine samples from 29 Ramadan fasting volunteers, with each volunteer providing a sample at the beginning (RF1) and at the end (RF2) of an approximately 12 hours fast. The results obtained showed the frequency of MA detection for RF2 was 12 and 2-fold higher than for the non-fasting and RF1 groups, respectively. This suggests fasting may alter the pattern of arsenic metabolism and excretion. However, there was no significant difference (P> 0.05) in the average of total level of arsenic for RF1 (18.3 µg/g creatinine) and RF2 (17.7 µg/g creatinine). A relationship between excretion of arsenic and selenium in individuals exposed to background levels of arsenic and selenium was investigated through analysis of urine samples from 93 volunteers from Leicester, UK. A positive correlation between arsenic and selenium was found and the As:Se ratio was 0.7 ± 0.4. The intra-individual variation of As:Se ratio does not alter significantly over time, as determined by monitoring urine samples from a volunteer over a period of one year. Furthermore, within a single day, with urine samples collected at the beginning and after a 12-hour fast, the As:Se ratio was found to be similar (0.7 ± 0.5). These findings suggest a close relationship between these two metalloids, the biological significance of which needs to be explored in the future.

Propõe-se, pela primeira vez, a associação do tratamento fotocatalítico de amostra, direcionado à degradação e/ou eliminação de interferentes orgânicos, com a separação analito/matriz via geração de hidretos voláteis seguida de determinação por espectrometria de absorção atômica (HG-AAS). O fotocatalisador TiO2 (P-25) foi utilizado sempre em suspensão na amostra, e como fonte de radiação UV empregou-se lâmpada de mercúrio. Duas geometrias de reator fotocatalítico foram examinadas: irradiação estacionária de amostras contidas em cubetas de quartzo (3,5 mL); e irradiação em reator tubular constituído de bobina de Teflon montada em torno da lâmpada. Para avaliar a eficiência do tratamento sob diferentes condições, utilizou-se inicialmente o sistema-modelo Cd(II)-EDTA, com detecção do Cd(II) não quelado por voltametria de pulso diferencial em eletrodo de gota pendente de mercúrio, sabidamente não influenciada pelo TiO2 em suspensão. Nos estudos com HG-AAS, focalizou-se a aplicação do tratamento fotocatalítico à decomposição da arsenobetaína (Asb), um composto modelo interessante por ser refratário aos tratamentos convencionais (micro-ondas + digestão ácida). As condições selecionadas para a etapa de HG-AAS foram: concentração de HCl, 3 mol.L-1, concentração de NaBH4, 1% m/v em NaOH 0,1 mol.L-1, volume de amostra, 0,10 mL e temperatura do atomizador de tubo de quartzo, 980 °C. Nessas condições, as curvas de calibração obtidas por HG-AAS para As(III) e As(V) na faixa de 0,020 a 0,100 mg.L-1 (20 a 100 ppb) apresentaram linearidade e sensibilidade próximas, indicando eficiência de formação similares, característica esta favorável à quantificação total de arsênio em aplicações futuras a amostra reais. Estudos preliminares mostraram que a taxa de recuperação do arsênio é maior no tratamento fotocatalítico realizado em meio alcalino, (pH=12) em razão da menor tendência à adsorção de arsênio em TiO2 nesse meio frente ao neutro e ácido. Parâmetros como o tempo de irradiação, concentração do fotocatalisador e de Asb, além da influência de O2 molecular como scavenger de elétrons também foram investigados. Nas condições selecionadas, partindo-se de uma solução de Asb 0,075 mg.L-1 em arsênio, alcançou-se recuperação aproximada de 80% mediante irradiação por 15 minutos e de 100% após 45 minutos. A decomposição da Asb pelo método fotocatalítico proposto foi confirmada por espectrometria de massa com ionização por electrospray e estudos adicionais poderão revelar se as espécies de arsênio envolvidas na geração da arsina encontram-se completamente mineralizadas. / The combination of photocatalytic sample preparation, aiming degradation of organic interferences, with analyte/matrix separation by generation of volatile hydrides followed by atomic absorption spectrometric determination (HG-AAS) is proposed for the first time in this work, mainly devoted to the investigation of total arsenic analysis. A mercury lamp served as source of UV-radiation and the photocatalyst, TiO2 (P25), was used as a suspension in the sample solution. Two geometries of photocatalytic reactor were examined: stationary irradiation of a set of samples contained in 3.5 mL quartz cuvettes (preferred one for the present application) and stopped-flow irradiation of a sample in a tubular reactor consisting of a Teflon tube coiled around the lamp. Evaluation of the digestion efficiency of the reactors under different conditions was made with help of the model system Cd(II)-EDTA, with detection of the unchelated Cd(II) by differential pulse voltammetry with the hanging mercury drop electrode, known to work in the presence of TiO2 suspension. The subsequent studies in combination with HG-AAS focused on the photocatalytic degradation of arsenobetaine (Asb), chosen as a model because it is particularly resistant to conventional treatments (microwave + acid digestion). The following conditions were established for the HG-AAS step: HCl concentration (3 mol.L-1) and NaBH4 concentration (1% m/v in NaOH 0,1 mol.L-1), sample volume (0.10 mL) and atomization temperature (980 °C). Calibration curves for As (III) and As (V) by HG-AAS in the range of 0,020 to 0,100 mg.L-1 (20 a 100 ppb) conveyed in slope and linearity, indicating the same efficiency of arsine formation from both species, favoring the total quantification of arsenic in the sample. Alkaline medium (pH=12) was preferred for the photocatalytic digestion because recoveries of arsenic were better than in neutral or acidic medium, possibly due to lower losses by adsorption of arsenic species on TiO2. The effects of parameters such as irradiation time, concentration of the photocatalyst and of arsenobetaine, as well as the influence of molecular O2 as an electron scavenger were investigated. Under selected conditions and for a starting solution of 0,075 mg.L-1 Asb an arsenic recovery of 80% approximately was obtained after 15 minutes of irradiation while full recovery required 45 minutes. The decomposition of the Asb molecule after irradiation was confirmed by electrospray mass spectrometry and a further study may reveal if the arsenic species involved in the arsine generation are fully mineralized ones.

Propõe-se, pela primeira vez, a associação do tratamento fotocatalítico de amostra, direcionado à degradação e/ou eliminação de interferentes orgânicos, com a separação analito/matriz via geração de hidretos voláteis seguida de determinação por espectrometria de absorção atômica (HG-AAS). O fotocatalisador TiO2 (P-25) foi utilizado sempre em suspensão na amostra, e como fonte de radiação UV empregou-se lâmpada de mercúrio. Duas geometrias de reator fotocatalítico foram examinadas: irradiação estacionária de amostras contidas em cubetas de quartzo (3,5 mL); e irradiação em reator tubular constituído de bobina de Teflon montada em torno da lâmpada. Para avaliar a eficiência do tratamento sob diferentes condições, utilizou-se inicialmente o sistema-modelo Cd(II)-EDTA, com detecção do Cd(II) não quelado por voltametria de pulso diferencial em eletrodo de gota pendente de mercúrio, sabidamente não influenciada pelo TiO2 em suspensão. Nos estudos com HG-AAS, focalizou-se a aplicação do tratamento fotocatalítico à decomposição da arsenobetaína (Asb), um composto modelo interessante por ser refratário aos tratamentos convencionais (micro-ondas + digestão ácida). As condições selecionadas para a etapa de HG-AAS foram: concentração de HCl, 3 mol.L-1, concentração de NaBH4, 1% m/v em NaOH 0,1 mol.L-1, volume de amostra, 0,10 mL e temperatura do atomizador de tubo de quartzo, 980 °C. Nessas condições, as curvas de calibração obtidas por HG-AAS para As(III) e As(V) na faixa de 0,020 a 0,100 mg.L-1 (20 a 100 ppb) apresentaram linearidade e sensibilidade próximas, indicando eficiência de formação similares, característica esta favorável à quantificação total de arsênio em aplicações futuras a amostra reais. Estudos preliminares mostraram que a taxa de recuperação do arsênio é maior no tratamento fotocatalítico realizado em meio alcalino, (pH=12) em razão da menor tendência à adsorção de arsênio em TiO2 nesse meio frente ao neutro e ácido. Parâmetros como o tempo de irradiação, concentração do fotocatalisador e de Asb, além da influência de O2 molecular como scavenger de elétrons também foram investigados. Nas condições selecionadas, partindo-se de uma solução de Asb 0,075 mg.L-1 em arsênio, alcançou-se recuperação aproximada de 80% mediante irradiação por 15 minutos e de 100% após 45 minutos. A decomposição da Asb pelo método fotocatalítico proposto foi confirmada por espectrometria de massa com ionização por electrospray e estudos adicionais poderão revelar se as espécies de arsênio envolvidas na geração da arsina encontram-se completamente mineralizadas. / The combination of photocatalytic sample preparation, aiming degradation of organic interferences, with analyte/matrix separation by generation of volatile hydrides followed by atomic absorption spectrometric determination (HG-AAS) is proposed for the first time in this work, mainly devoted to the investigation of total arsenic analysis. A mercury lamp served as source of UV-radiation and the photocatalyst, TiO2 (P25), was used as a suspension in the sample solution. Two geometries of photocatalytic reactor were examined: stationary irradiation of a set of samples contained in 3.5 mL quartz cuvettes (preferred one for the present application) and stopped-flow irradiation of a sample in a tubular reactor consisting of a Teflon tube coiled around the lamp. Evaluation of the digestion efficiency of the reactors under different conditions was made with help of the model system Cd(II)-EDTA, with detection of the unchelated Cd(II) by differential pulse voltammetry with the hanging mercury drop electrode, known to work in the presence of TiO2 suspension. The subsequent studies in combination with HG-AAS focused on the photocatalytic degradation of arsenobetaine (Asb), chosen as a model because it is particularly resistant to conventional treatments (microwave + acid digestion). The following conditions were established for the HG-AAS step: HCl concentration (3 mol.L-1) and NaBH4 concentration (1% m/v in NaOH 0,1 mol.L-1), sample volume (0.10 mL) and atomization temperature (980 °C). Calibration curves for As (III) and As (V) by HG-AAS in the range of 0,020 to 0,100 mg.L-1 (20 a 100 ppb) conveyed in slope and linearity, indicating the same efficiency of arsine formation from both species, favoring the total quantification of arsenic in the sample. Alkaline medium (pH=12) was preferred for the photocatalytic digestion because recoveries of arsenic were better than in neutral or acidic medium, possibly due to lower losses by adsorption of arsenic species on TiO2. The effects of parameters such as irradiation time, concentration of the photocatalyst and of arsenobetaine, as well as the influence of molecular O2 as an electron scavenger were investigated. Under selected conditions and for a starting solution of 0,075 mg.L-1 Asb an arsenic recovery of 80% approximately was obtained after 15 minutes of irradiation while full recovery required 45 minutes. The decomposition of the Asb molecule after irradiation was confirmed by electrospray mass spectrometry and a further study may reveal if the arsenic species involved in the arsine generation are fully mineralized ones.

La pollution en As dans le monde et son impact sont tels qu'il est essentiel de comprendre les processus de contrôle de sa dynamique, notamment dans les zones humides identifiées comme source potentielle. L'objectif de cette thèse a été d'étudier les produits de réoxydation du sol d'une zone humide et la spéciation associée de l'As. La spéciation de l'As a tout d'abord été étudiée dans les produits d'oxydation collectés dans un sol de zone humide (Naizin-Kervidy, France). Les analyses en spectroscopie d'absorption aux RX (XAS) ont montré que l'As était partiellement oxydé. La persistance de l'As (III) a été expliquée par le contrôle de la MO sur les phases de Fe porteuses de l'As, responsables de son oxydation. Le Fe forme des nano-oxydes, des petits polymères, et monomères de Fe complexés aux molécules organiques ce qui limite la densité de sites oxydants. Une deuxième partie a portée sur les produits de réoxydation avant agrégation. Les composants particulaires, colloïdaux et solubles ont été fractionnés et les éléments associés déterminés (XAS, HPLC-ICP-MS, THM-GC-MS). L'As est majoritairement sous forme d'As(V) inorganique et organique (DMA et arsénobétaine). Ces dernières sont produites des processus biologiques de détoxification. La fraction riche en nano-oxydes, petits polymères/monomères de Fe liés à la MO est très réactive vis-à-vis de l'As. La composition de la MO varie, d'une MO d'origine végétale moins complexante dans les grosses fractions elle passe à de la MO humique très complexante favorisant la formation de petites structures de Fe. Un bilan de masse montre que 90 % de l'As est présent dans les fractions particulaires très peu mobiles. La fraction colloïdale Fe-MO est critique car les concentrations en As sont substantielles et elle est facilement mobilisable. Les agrégats Fe-MO contrôlent donc la mobilité de l'As en solution et il est essentiel de mieux appréhender l'influence de la structure physique sur les processus d'adsorption de l'As. Des agrégats Fe/MO ont été synthétisés pour des rapports croissants Fe/MO. Le Fe forme des agrégats fractals. Une bille primaire constitue des agrégats intermédiaires qui eux-mêmes forment des agrégats secondaires. Ces derniers sont constitués d'une partie Fe et d'une partie MO qui correspond à un agrégat sphérique dense. Avec l'augmentation du ratio Fe/MO, la taille des composantes Fe et MO augmentent et la structure des gros agrégats devient moins dense suite à l'augmentation des forces de répulsion entre les agrégats intermédiaires. Le recouvrement de la MO sur les agrégats de Fe diminue. Ces changements de structure permettent d'augmenter l'adsorption de l'As car la disponibilité des sites de sorption augmentent. Ces résultats sont intéressants à mettre en perspective avec les solutions naturelles où les rapports Fe/OC varient temporellement et spatialement. / Regards to the extent of the As pollution in the world and its impact on human health, the processes controlling its dynamic had to be investigated, especially in wetlands, recently recognized as potential As source for groundwater. The objective of this work was to study the oxidation products of a wetland and the associated As speciation. In a first part, natural oxidation products collected in a wetland soil (Naizin-Kervidy, France) were studied. The solids analyzed by XAS showed that As was partially oxidized. The As (III) persistence was explained by the control exercised by MO on the Fe bearing phases of As responsible also for its oxidation. Iron formed nano-oxides, small polymers or monomers complexed to organic molecules. The small size of Fe phases limits the density of the As oxidizing sites. In the second part, the reoxidation products before their aggregation in soil were studied. Particulate, colloid and soluble fractions and their associated elements were analyzed by XAS, HPLC-ICP-MS, THM-GC-MS. The As was predominantly as inorganic As (V) and organic As (V) (Arsenobetaine and DMA) the latter being produced by biological detoxification process. The fraction enriched in Fe nano-oxides or small polymers/monomers bound to the OM was highly reactive against As. The composition of the OM varied from fresh vegetal and less complexing OM in particulate fraction to humic and highly complexing OM in lower fractions. In mass proportion, more than 90% of As was in the few mobile particulate fractions. The colloidal fraction remained however critical regards its substantial As concentration and its strong mobility potential. The Fe-OM aggregates seem to control As dynamics in solution, studying the influence of the aggregate structure on the As sorption processes is therefore critical. Aggregates of Fe/OM at increasing Fe/OM ratio were synthetized. Iron forms fractal aggregates. Primary beads formed intermediate aggregates (both being bound to diffuse organic molecules), themselves forming (or not) larger secondary aggregates. This latter was composed of a Fe part corresponding to the aggregated intermediate aggregates and an OM part organized as a spherical dense aggregate. With the increasing Fe/OM ratio, Fe and OM part increased and large aggregates become less dense with the increasing repulsion forces between each intermediate aggregates. The coating of the OM on Fe intermediate aggregates within the secondary aggregates decreased. These structural changes led to an increase of the As binding in response to the increasing availability of the binding site.