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There is not, at this time, a simple method for the simultaneous determination of As (III) and As (V) at trace levels. The development of such as method is needed, as the toxicities of these two species differ so greatly. As (III) and As (V) are polarographically reducible in the presence of excess catechol, but the wave produced by As (V) is depended on time, pH and catechol concentration as well as As (V) concentration. In order to understand this behavior, determination of formation constants for any complex species present were needed to identify which species is electroactive. The literature to date on the subject of As (V) – catechol compounds has shown that there is not a thorough understanding of what species are present and what their stabilities are.

Arsenic is found in the environment in several oxidation states as well as in a variety of organoarsenic compounds. This situation puts additional demands on the analysis in that it is desirable to measure the amount of each species, not just all of the arsenic. The reason for this is that the different species have greatly different toxicities; of the major inorganic forms, As(III) is much more toxic than As(V). The goal of this research was to develop a convenient method for the analysis of mixtures of As(III) and As(V) at trace levels. Electroanalytical methods are inherently sensitive to oxidation states of elements and therefore are a natural choice for this problem. In fact, a method was developed some years ago for As(III) that used differential pulse polarography: the detection limit is 0.3 parts per billion (ppb). However, As(V) was not detected since in its usual form as an oxyanion it is electrochemically inactive. There are coordinate compounds formed with catechol, AsL(,n)(n = 1-3), that can be reduced at a mercury electrode, but the active species, AsL, is only a small fraction of the major species, AsL(,3), so the detection limit is only 500 ppb. Many details of the electrochemistry of this unusual compound were examined in this work. In order to improve detection limits, a method involving cathodic stripping was developed. It involves codeposition of copper with arsenic on a mercury electrode to effectively concentrate the analyte. Then the elemental arsenic is converted to arsine, AsH(,3), during a cathodic potential scan. The resulting current peak is proportional to As(III) in the absence of catechol and to the sum of As(III) and As(V) in the presence of catechol. It was observed that the current peak was considerably larger than expected and additional experiments revealed that there was evolution of hydrogen during the formation of arsine. This is rather unusual in electrochemical reactions and so some of the details of this catalyzed coreaction were examined. The result is a fortunate enhancement of detection limit so that As(v) at 40 ppb can be measured.

Capillary-based analytical methodologies were developed to meet the need for metabolite determination in two major areas. The first area is the determination of free bilirubin in sera for the management of jaundiced neonates under critical conditions. Three sensitive detection techniques were investigated, Quantum dots (QD) mediated fluorescence, Chemiluminescence (CL) and Microelectrode detection. Four different types of QDs were synthesized for the direct bilirubin determination. The CAH-capped CdTe QDs were selected as it shows the best performance compared to organic dyes and other QDs. Its optimized preparation conditions are: refluxing solution containing Cd/Te/CAH (1:0.5:2.4 w/w) for 4 hours at 100 °C. From Transmission Electron Microscope characterization, nano-size QDs with an uniform size distribution, high luminescence and good stability were obtained. The optimized detection conditions were: incubation of bilirubin with CAH-capped CdTe QDs (5 10-6 mol/L) in water at pH=5.6 and 20 oC for 8 min prior to spectrofluorometric determination (λex=473 nm and λem=580 nm). A linear working range from 0.043-0.86 μg/mL with 0.9943 correlation coefficient and 2 ng/mL detection limit (LOD, S/N=3) were achieved. Results from nFIA-CL indicate a quick response within seconds though a poorer LOD (S/N=3) of 15 μg/mL for the direct bilirubin determination. The third technique investigated used an enzyme microelectrode and it was found to be able to couple with capillary electrophoresis (CE) in frontal analysis (FA) for the determination of free bilirubin in serum samples. Making use of the micron size of the carbon-fiber electrode, a new MCNTs (Multi-wall Carbon Nanotubes) modified CFMEs (Carbon fiber microelectrodes) was fabricated within a microchip-CE device with three guided channels to enable electrodes alignment. Method to immobilize bilirubin oxidase (BOD) onto the CFMEs surface by the carbodiimide chemistry achieved the highest detection sensitivity. Under optimized conditions (sample introduced by hydrodynamic injection at △H (20 cm), and a running/detection buffer (10 mM phosphate) at pH 7.4, working potential for amperometric detection at +0.8 V), a linear working range between 1-40 μg/mL and a detection limit (S/N=3) at 0.15 μg/mL for free bilirubin was achieved. The second area for metabolite determination was developing a new analytical method for the management of APL (acute promyelocytic leukemia) patients under arsenic treatment, a drug required continued monitoring. The analytical requirements include a high detection sensitivity and the capability to provide timely results for multiple drug residues. Using a 20 mM phosphate as the running buffer and 0.05mM CTAH (Cetyl-trimethyl-ammonium hydroxide) as an additive for EOF reversal, co-EOF (co-electroosmotic flow) stacking was established to enhance up to 200 times of the detection limit for arsenite. Satisfactory baseline separation for arsenite, arsenate, MMA (Methylarsonic acid) and DMA (Dimethylarsinic acid) was achieved with linear working ranges (correlation coefficients > 0.999) from 1-50 μg/mL for arsenate and DMA, 0.5-50 μg/mL for MMA as well as 0.1-50 μg/mL for arsenite. Detection limits (S/N=3, n=3) achievable for arsenate, arsenite, MMA and DMA were found to be 0.41 μg/mL, 0.01 μg/mL, 0.04 μg/mL and 0.32 μg/mL respectively at levels meeting the requirement for APL patient urine monitoring. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Arsenic is a known carcinogen, but is persistent in the environment, remaining a popular pesticide. It represents a particular hazard to humans when it stays resident in shallow soils and groundwater. This study of contaminant hydrogeology examined conditions at a former golf course in Florida with known arsenic contamination, and included a detailed examination of existing assessment data for the study area, an experimental pumping test with groundwater sampling, examination of sediment cores, and a preliminary geophysical investigation. The primary purpose was to determine what the existing controls are on As mobility. The primary findings were that redox conditions did have an effect on As concentrations. Groundwater in the study area is generally reducing, but during the pumping test was generally oxidizing. No potential As sources were definitively identified, and the most likely source remains anthropogenic, but interactive conditions with Fe, Mn, NO3-N, and S remain nebulous. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

published_or_final_version / abstract / Anatomy / Doctoral / Doctor of Philosophy

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.