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Effect of organic matter on determination of reactive mercury in contaminated waters

Ramalhosa, Elsa; Río-Segade, Susana; Pereira, Eduarda; Vale, Carlos; Duarte, Armando
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.1%
Dissolved reactive mercury was determined in water samples from Ria da Aveiro, a coastal lagoon contaminated by mercury. Concentrations increased with acid dilution to a maximum of 193% in samples containing organic matter with high aromaticity, as inferred from absorbances at 250, 280 and 365 nm. Laboratory experiments with potassium hydrogenoftalate and humic acids solutions proved the influence of aromaticity in complexing mercury, how acid dilution protonates the aromatic Hg-complexes and consequent release of labile forms of mercury to solution. On the basis of these results it is proposed that natural waters from mercury contaminated ecosystems should be analysed without dilutions, otherwise additional studies should be performed to access the protonation of mercury organic complexes.

Cloud point extraction and concentration of carbaryl from natural waters

MELCHERT, Wanessa R.; ROCHA, Fabio R. P.
Fonte: TAYLOR & FRANCIS LTD Publicador: TAYLOR & FRANCIS LTD
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.15%
An improved procedure is proposed for determination of the pesticide carbaryl in natural waters based on double cloud point extraction. The clean up step was carried out only with Triton X-114 in alkaline medium in order to avoid the use of toxic organic solvents as well as to minimise waste generation. Cloud point preconcentration of the product of the reaction of the analyte with p-aminophenol and cetyltrimethylammonium bromide was explored to increase sensitivity and improve the detection limit. Linear response was achieved within 10 and 500 mu g L-1 and the apparent molar absorptivity was estimated as 4.6 x 105 L mol-1 cm-1. The detection limit was estimated as 7 mu g L-1 at the 99.7% confidence level and the coefficient of variation was 3.4% (n = 8). Recoveries within 91 and 99% were estimated for carbaryl spiked water samples. The results obtained for natural water samples were in agreement with those achieved by the batch of spectrophotometric procedure at the 95% confidence level. The proposed procedure is then a simple, fast, inexpensive and greener alternative for carbaryl determination.; Brazilian agencies Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)

A multicommuted flow system with solenoid micro-pumps for paraquat determination in natural waters

INFANTE, Carlos M. C.; MORALES-RUBIO, A.; GUARDIA, M. de la; ROCHA, Fabio R. P.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.15%
A flow system designed with solenoid micro-pumps is proposed for the determination of paraquat in natural waters. The procedure involves the reaction of paraquat with dehydroascorbic acid followed by spectrophotometric measurements. The proposed procedure minimizes the main drawbacks related to the standard chromatographic procedure and to flow analysis and manual methods with spectrophotometric detection based on the reaction with sodium dithionite, i.e. high solvent consumption and waste generation and low sampling rate for chromatography and high instability of the reagent in the spectrophotometric procedures. A home-made 10-cm optical-path flow cell was employed for improving sensitivity and detection limit. Linear response was observed for paraquat concentrations in the range 0.10-5.0 mg L-1. The detection limit (99.7% confidence level), sampling rate and coefficient of variation (n = 10) were estimated as 22 mu g L-1, 63 measurements per hour and 1.0%, respectively. Results of determination of paraquat in natural water samples were in agreement with those achieved by the chromatographic reference procedure at the 95% confidence level. (c) 2008 Elsevier B.V. All rights reserved.

Desenvolvimento de metodologias para determinação de resíduos de atrazina em solos e águas naturais empregando técnicas eletroanalíticas.; Development of methodologies for determination of residues of atrazine in soil and natural waters employing electroanalytical techniques.

Santos, Luciana Bagdeve de Oliveira dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/04/2006 Português
Relevância na Pesquisa
56.21%
Esta tese descreve o desenvolvimento de metodologias eletroanalíticas, em especial a voltametria de onda quadrada com o eletrodo de gota pendente de Hg, para determinação de atrazina em águas de rios do Estados de São Paulo e em amostras de solo. A exatidão das metodologias foi avaliada por comparação com HPLC e estudos de recuperação. Inicialmente desenvolveu-se o método em modo estático, no qual a maior sensibilidade foi obtida em pH 2 e freqüência de 400 Hz, com limites de detecção e determinação de 2 e 10 microgramas L-1, respectivamente. O estudo do comportamento eletroquímico revelou que a atrazina comporta-se reversivelmente em altas freqüências de onda quadrada. Dentre os metabólitos da atrazina, a desetilatrazina e desiosopropilatrazina, também são eletroativas nas condições estudadas, sendo possíveis interferentes, ao contrário da hidroxiatrazina e didealquilatrazina. Sistemas em fluxo contínuo e de injeção seqüencial foram desenvolvidos para determinação de atrazina em extrato de solo e águas naturais, bem como em estudos de adsorção. Em águas, os limites de detecção e determinação obtidos por injeção seqüencial foram de 4,5 e 15 microgramas L-1. Estudos de adsorção revelaram que atrazina liga-se mais fortemente a solos em meios ácidos. As metodologias em fluxo permitiram um significativo aumento da velocidade analítica e economia de reagentes...

Estudo estatístico do desempenho analítico das técnicas eletroquímicas VPD, VOQ e MVOQ para a redução do herbicida paraquat em UME-Au e sua quantificação em águas puras e naturais; Statistic study of the analytical performance of DPV, SWV and MSWV electrochemical techniques for the reduction of the paraquat herbicide on an Au-UME and its analysis and quantification in pure and natural waters

Silva, Osmair Benedito da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/01/2008 Português
Relevância na Pesquisa
66.3%
Neste trabalho foi realizado um estudo estatístico do desempenho analítico das técnicas eletroquímicas Voltametria de pulso diferencial (VPD), Voltametria de onda quadrada (VOQ) e Voltametria de múltiplas ondas quadradas (VMOQ) para a redução do herbicida paraquat em ultramicroeletrodo de ouro (UME-Au) e sua análise e quantificação em águas puras e naturais. Os estudos da redução eletroquímica do paraquat foram realizados em eletrólito de suporte Na2SO4 0,1 mol L-1 em pH = 5,5. Os resultados mostraram a presença de dois picos de redução bem definidos , com o pico 1 em -0,64 V e o pico 2 em -0,94 V vs Ag/AgCl 3,0 mol L-1. Para as análises foi utilizado o pico 1 que é referente a uma reação em solução, onde a superfície eletródica serve apenas como intermediadora na transferência eletrônica. Utilizando-se os parâmetros experimentais e voltamétricos otimizados, curvas de trabalho foram construídas em eletrólito de suporte preparado com água ultrapurificada. Para a VPD, VOQ e VMOQ, os limites de detecção encontrados utilizando-se o método descrito em Miller & Miller e considerando-se o pico 1 foram: 55,35 ± 0,18 µg L-1 , 37,50 ± 0,32 µg L-1 e 21,42 ± 0,51 µg L-1, respectivamente. A metodologia foi aplicada em amostras de águas coletadas no Rio Mogi-Guaçu na cidade de São Carlos-SP. A variação da inclinação das curvas de trabalho obtida nas análises destas amostras foi praticamente insignificante em relação àquela obtida utilizando-se o eletrólito de suporte preparado com água ultrapurificada para as três técnicas utilizadas...

Ultramicroeletrodo de irídio com filme de mercúrio eletrodepositado para medidas in situ de íons metálicos e pesticidas em solos e águas naturais; Iridium based ultramicroelectrodes with an electro-platted mercury film for in situ determination of metallic ions and pesticides in soil and natural waters

Silva Júnior, Paulo Roberto Vieira da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/06/2009 Português
Relevância na Pesquisa
66.24%
Neste trabalho foram desenvolvidas metodologias para a determinação de substâncias de interesse, como metais pesados (micronutrientes e contaminantes), macronutrientes e pesticidas em solo e águas naturais com ultramicroeletrodo de irídio recoberto com filme de Hg eletrodepositado (UME Ir-Hg) e técnicas voltamétricas, utilizando uma cápsula porosa de cerâmica como cela eletroquímica. As metodologias de medidas com os ultramicroeletrodos foram desenvolvidas inicialmente em condições controladas e posteriormente aplicadas a medidas in-situ, com experimentos com águas naturais e solos, conduzidos em laboratório e também com posteriores medidas em amostras reais. Segundo os resultados obtidos foi possível explorar as metodologias voltamétricas, principalmente as de pulso e redissolução anódica, como ferramentas para estudos in-situ dos metais Cd(II), Pb(II) e Cu(II) e do inseticida organofosforado paration metílico, substâncias de grande interesse, obtendo-se um bom nível de repetibilidade e sensibilidade, com limites de detecção em amostras reais de centenas de ppb's.; In this work a methodology for determination of metallic ions (micronutrients and contaminants), macronutrients and pesticides in soil and natural waters was developed using an Hg plated iridium based ultramicroelectrode and voltammetric techniques...

Spectrophotometric determination of zinc and copper in a multisyringe injection analysis system using a liquid waveguide capillary cell: Application to natural waters

Páscoa, Ricardo N.M.J.; Tóth, Ildikó V.; Rangel, António O.S.S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
Relevância na Pesquisa
66.21%
This work exploits a multisyringe injection analysis (MSFIA) system coupled with a long liquid waveguide capillary cell for the spectrophotometric determination of zinc and copper in waters. A liquid waveguide capillary cell (1.0mpathlength, 550mmi.d. and 250mL internal volume) was used to enhance the sensitivity of the detection. The determination for both ions is based on a colorimetric reaction with zincon at different pH values. The developed methodology compares favourably with other previously described procedures, as it allows to reach low detection limits for both cations (LODs of 0.1 and 2mg L−1, for copper and zinc, respectively), without the need for any preconcentration step. The system also provided a linear response up to 100mg L−1 with a high throughput (43 h−1) and low reagent consumption and effluent production. The developed work was applied to natural waters and three certified reference water samples.

Effect of organic matter on determination of reactive mercury in contaminated waters

Ramalhosa, E.; Segade, S. R.; Pereira, E.; Vale, C.; Duarte, A.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.1%
Dissolved reactive mercury was determined in water samples from Ria da Aveiro, a coastal lagoon contaminated by mercury. Concentrations increased with acid dilution to a maximum of 193% in samples containing organic matter with high aromaticity, as inferred from absorbances at 250, 280 and 365 nm. Laboratory experiments with potassium hydrogenoftalate and humic acids solutions proved the influence of aromaticity in complexing mercury, how acid dilution protonates the aromatic Hg-complexes and consequent release of labile forms of mercury to solution. On the basis of these results it is proposed that natural waters from mercury contaminated ecosystems should be analysed without dilutions, otherwise additional studies should be performed to access the protonation of mercury organic complexes.

VALIDAÇÃO INTRALABORATORIAL DA DETERMINAÇÃO DE METILTESTOSTERONA EM ÁGUAS NATURAIS POR VOLTAMETRIA USANDO ELETRODO DE GOTA PENDENTE DE MERCÚRIO

Miranda,Luciane; Felsner,Maria L.; Torres,Yohandra R.; Hoss,Ivonete; Galli,Andressa; Quináia,Sueli P.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2015 Português
Relevância na Pesquisa
46.24%
17α-methyltestosterone (17α-MT) is a hormone used in medicine and aquaculture which can be found in natural waters. It is considered an emerging organic pollutant and its accurate and precise analysis is required. Therefore, this study presents the in-house validation of a new voltammetric methodology for 17α-MT analysis in natural waters. A hanging mercury drop electrode and NaOH 5.0×10-3 mol L-1 solution as the electrolyte were employed in the voltammetric determinations. To confirm the presence of 17α-MT in water samples quantitative analysis was performed by ESI-MS/MS. The methodology exhibited good selectivity, linearity, accuracy (recovery of between 100.4 and 108.8%) and precision (RSDs for repeatability of 2.85% and for intermediate precision of 14.10%, with n = 5, respectively). LOD and LOQ were 3.07 µg L-1 and 10.78 µg L-1, respectively. The methodology was suitable for determination of 17α-MT in natural waters due to low-cost, good performance and no sample pre-treatment required.

Selective reduction of arsenic species by hydride generation - atomic absorption spectrometry. Part 2 - sample storage and arsenic determination in natural waters

Quináia,Sueli P.; Rollemberg,Maria do Carmo E.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2001 Português
Relevância na Pesquisa
66.15%
Total arsenic, arsenite, arsinate and dimethylarsinic acid (DMA) were selectively determined in natural waters by hydride generation - atomic absorption spectrometry, using sodium tetrahydroborate(III) as reductant but in different reduction media. River water samples from the north region of Paraná State, Brazil, were analysed and showed arsenate as the principal arsenical form. Detection limits found for As(III) (citrate buffer), As(III) + DMA (acetic acid) and As(III) + As(V) (hydrochloric acid) were 0.6, 1.1 and 0.5 mg As L-1, respectively. Sample storage on the proper reaction media revealed to be a useful way to preserve the water sample.

Ammonium ion sensor based on SiO2/ZrO2/phosphate-NH4+ composite for quantification of ammonium ions in natural waters

Coutinho,Cláudia F. B.; Muxel,Alfredo A.; Rocha,Crystian G.; Jesus,Débora A. de; Alfaya,Rení V. S.; Almeida,Flaveli A. S.; Gushikem,Yoshitaka; Alfaya,Antonio A. S.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 Português
Relevância na Pesquisa
66.34%
Ion selective-electrode was constructed and evaluated for determination of ammonium ions in natural waters. The electrode consists of paste carbon with the composite SiO2/ZrO2/phosphate-NH4+ obtained through sol-gel process. The electrode exhibits a sub-Nernstian response for ammonium concentrations between 7.7´10-7 and 4.0´10-2 mol L-1 and a detection limit of 1.58´10-7 mol L-1 (8.5´10-3 ppm). The electrode response for ammonium was fast (1 minute). The selectivity coefficients KpotA,B for several ions usually present in natural waters were determined applying the matched potential method. The potentiometric method with the ion selective electrode was validated by the Berthelot method (standard method), through the determination of ammonium ions in natural waters. The ion selective-electrode proved suitable for routine quality control of natural waters by potentiometry.

Direct electrochemical analysis of dexamethasone endocrine disruptor in raw natural waters

Oliveira,Thiago M. B. F.; Ribeiro,Francisco W. P.; do Nascimento,Jefferson M.; Soares,Janete E. S.; Freire,Valder N.; Becker,Helena; Lima-Neto,Pedro de; Correia,Adriana N.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 Português
Relevância na Pesquisa
66.24%
This paper describes an electroanalytical methodology using square-wave adsorptive voltammetry, which has been successfully applied for the direct determination of dexamethasone residues in raw natural waters used for the public supply of the Ceará State, Brazil. The obtained detection limits ranged from 7.47 × 10-9 to 1.80 × 10-8 mol L-1 for the three matrices of raw natural waters evaluated. High percentages of average recovery (98.86% ± 0.72), repeatability (0.32% ± 0.05) and reproducibility (0.91% ± 0.20) were obtained in these samples, reaffirming the sensitivity of the procedure. Energy of the LUMO orbitals and Mülliken’s atomic charges were calculated using the functional BLYP/DNP. The theoretical results allied to the diagnostic criteria of the square-wave voltammetry indicate that the dexamethasone redox mechanism is associated to the quasi-reversible and irreversible reduction process of the ketone groups located at C-20 and C-3, respectively.

Immunomagnetic Separation (IMS)-Fluorescent Antibody Detection and IMS-PCR Detection of Seeded Cryptosporidium parvum Oocysts in Natural Waters and Their Limitations

Sturbaum, Gregory D.; Klonicki, Patricia T.; Marshall, Marilyn M.; Jost, B. Helen; Clay, Brec L.; Sterling, Charles R.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /06/2002 Português
Relevância na Pesquisa
46.24%
Detection and enumeration of Cryptosporidium parvum in both treated and untreated waters are important to facilitate prevention of future cryptosporidiosis incidents. Immunomagnetic separation (IMS)-fluorescent antibody (FA) detection and IMS-PCR detection efficiencies were evaluated in two natural waters seeded with nominal seed doses of 5, 10, and 15 oocysts. IMS-FA detected oocysts at concentrations at or below the three nominal oocyst seed doses, illustrating that IMS-FA is sensitive enough to detect low oocyst numbers. However, the species of the oocysts could not be determined with this technique. IMS-PCR, targeting the 18S rRNA gene in this study, yielded positive amplification for 17 of the 18 seeded water samples, and the amplicons were subjected to restriction fragment length polymorphism digestion and DNA sequencing for species identification. Interestingly, the two unseeded, natural water samples were also PCR positive; one amplicon was the same base pair size as the C. parvum amplicon, and the other amplicon was larger. These two amplified products were determined to be derived from DNA of Cryptosporidium muris and a dinoflagellate. These IMS-PCR results illustrate that (i) IMS-PCR is able to detect low oocyst numbers in natural waters...

A Modified o-Phthalaldehyde Fluorometric Analytical Method for Ultratrace Ammonium in Natural Waters Using EDTA-NaOH as Buffer

Hu, Hongzhi; Liang, Ying; Li, Shuo; Guo, Qing; Wu, Chancui
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.24%
In the existence of appropriate amount of disodium ethylenediaminetetraacetate (EDTA), precipitation would not occur in seawater and other natural waters even if the sample solution was adjusted to strong basicity, and the NH3-OPA-sulfite reaction at the optimal pH range could be used to determine ammonium in natural waters. Based on this, a modified o-phthalaldehyde fluorometric analytical method has been established to determine ultratrace ammonium in natural waters. Experimental parameters, including reagent concentration, pH, reaction time, and effect of EDTA, were optimized throughout the experiments based on univariate experimental design. The results showed that the optimal pH range was between 10.80 and 11.70. EDTA did not obviously affect the fluorometric intensity. The linearity range of the proposed method was 0.032–0.500 µmol/L, 0.250–3.00 µmol/L, and 1.00–20.0 µmol/L at the excitation/emission slit of 3 nm/5 nm, 3 nm/3 nm, and 1.5 nm/1.5 nm, respectively. The method detection limit was 0.0099 µmol/L. Compared to the classical OPA method, the proposed method had the advantage of being more sensitive and could quantify ultratrace ammonium without enrichment.

Online solid phase extraction liquid chromatography tandem mass spectrometry (SPE-LC-MS/MS) method for the determination of sucralose in reclaimed and drinking waters and its photo degradation in natural waters from South Florida

Butchu, Sudha Rani; Quinete, Natalia; Panditi, Venkata R.; Gardinali, Piero R.
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Português
Relevância na Pesquisa
56.31%
Background Sucralose has gained popularity as a low calorie artificial sweetener worldwide. Due to its high stability and persistence, sucralose has shown widespread occurrence in environmental waters, at concentrations that could reach up to several μg/L. Previous studies have used time consuming sample preparation methods (offline solid phase extraction/derivatization) or methods with rather high detection limits (direct injection) for sucralose analysis. This study described a faster and sensitive analytical method for the determination of sucralose in environmental samples. Results An online SPE-LC–MS/MS method was developed, being capable to quantify sucralose in 12 minutes using only 10 mL of sample, with method detection limits (MDLs) of 4.5 ng/L, 8.5 ng/L and 45 ng/L for deionized water, drinking and reclaimed waters (1:10 diluted with deionized water), respectively. Sucralose was detected in 82% of the reclaimed water samples at concentrations reaching up to 18 μg/L. The monthly average for a period of one year was 9.1 ± 2.9 μg/L. The calculated mass loads per capita of sucralose discharged through WWTP effluents based on the concentrations detected in wastewaters in the U. S. is 5.0 mg/day/person. As expected, the concentrations observed in drinking water were much lower but still relevant reaching as high as 465 ng/L. In order to evaluate the stability of sucralose...

Determination of trace aluminum in natural waters by ion exchanger fluorometry

Capit??n Garc??a, Ferm??n; Manzano Moreno, Elo??sa; V??lchez Quero, Jos?? Luis; Capit??n Vallvey, Luis Ferm??n
Fonte: Japan Society for Analytical Chemistry (JSAC) Publicador: Japan Society for Analytical Chemistry (JSAC)
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.06%
Morin (2???, 3, 4???, 5, 7-pentahydroxyflavone) has been used as a ligand in the fluorometric microdetermination of aluminum at the sub-??gl-1 level. A method has been developed which is based on ion exchanger fluorometry (IEF). The 1:1 aluminum-morin complex is fixed on a dextran-type cationic exchanger, and the fluorescence of the gel, packed on a 1-mm quartz cell, is measured directly using a solid-surface attachment. The concentration for the method ranges between 0.4 and 1.6??gl-1, although this can be diminished by increasing the sample volume. The method has been successfully applied to the determination of aluminum in natural water and offers several advantages in comparison with solution methods.

Hydroxyl radical production via the photo-Fenton reaction in natural waters

Southworth, Barbara A. (Barbara Anne), 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 188 leaves; 5518688 bytes; 5518494 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
46.42%
This dissertation investigates the importance of photo-Fenton chemistry in natural waters. The Fenton reaction, H202 + Fe(ll) [right arrow] Fe(ll) + OH- + OH', can occur in sunlit waters because both H202 and Fe(ll) are photo-chemically produced. Photo-Fenton chemistry was investigated by irradiating model systems and natural water samples with simulated sunlight and measuring both H202 accumulation and OH' production in the presence and the absence of Fe reactions. Using these data, a model was developed to calculate the potential impact of the photo-Fenton reaction in sunlit natural waters. Throughout this work, a method based on the chemiluminescent reaction of an acridinium ester compound with the conjugate base of H202 was used to analyze H202. This method is sensitive, and has a greater dynamic range, greater selectivity, and fewer sources of interference than more commonly used methods. However, its behavior is not consistent with a simple reaction mechanism. The kinetics of the chemiluminescent reaction were investigated and a mechanism proposed that can explain its behavior, confirming the ability of this method to accurately measure H202, and suggesting ways to avoid potential problems with its application. The photo-Fenton reaction was studied in model systems consisting of a standard humic substance and amorphous iron oxide exposed to simulated sunlight. A probe method was adapted to allow low concentrations of OH' to be measured without otherwise influencing the chemical reactions occurring in experiments. The difference between measured H202 accumulation in the presence and absence of Fe in these systems was interpreted as the photo-loss of H202 by reaction with Fe(ll).; (cont.) Both this photo-loss...

Metodologías combinadas de análisis en línea. Estudios de especiación de arsénico inorgánico en aguas subterráneas; Combined methodologies of analysis on line. Studies of inorganic arsenic speciation in underground waters

Sigrist, Mirna
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2009 Português
Relevância na Pesquisa
56.28%
El objetivo del presente trabajo es el estudio y la optimización de metodologías analíticas combinadas para la evaluación de arsénico total y sus especies inorgánicas a nivel de vestigios en aguas naturales. Las distintas estrategias se basaron en sistemas de inyección en flujo (FI) acoplados a generadores de hidruros (HG) y detectores atómicos (AAS) con atomizador de tubo de cuarzo (QT). Las metodologías para la "especiación" elemental de arsénico en aguas naturales desarrolladas en este trabajo fueron optimizadas en condiciones no usuales para FI-HG-QT-AAS con el objetivo de mantener la distribución original de especies existente en el momento del muestreo. En el Capítulo 1 se presenta un panorama actualizado del problema sanitario ocasionado por la presencia de arsénico en las aguas subterráneas utilizadas para consumo humano en diferentes regiones del planeta, la relación existente entre las características hidrogeológicas de los reservorios naturales y la especie arsenical predominante, los avances aportados por recientes estudios toxicológicos y epidemiológicos como así también, el estado de la reglamentación sobre el tema a nivel nacional e internacional. Las metodologías analíticas más utilizadas en la determinación de arsénico y sus especies son también presentadas y discutidas en este capítulo. En el Capítulo 2 se realiza una revisión detallada de las diferentes estrategias mencionadas en la literatura para la preservación de las especies metálicas a nivel de vestigios en muestras acuosas. Se presenta un muestreador para la extracción de agua subterránea destinada al análisis de "especiación"...

A Dynamic Model of Phytoplankton Populations in Natural Waters

DiToro, Dominic M.; O'Connor, Donald J.; Thomann, Robert V.
Fonte: Universidade de Delaware Publicador: Universidade de Delaware
Tipo: Relatório Formato: 4799622 bytes; application/pdf
Português
Relevância na Pesquisa
66.18%
This paper presents a phytoplankton population model in natural waters. This model is constructed on the basis of the principle of conservation of mass. This is an elementary physical law which is satisfied by microscopic natural systems. The use of this principle is dictated primarily by the lack of any more specific physical laws which can be applied to these biological systems. The use of this principle is dictated primarily by the lack of any more specific physical laws which can be applied to these biological systems. An alternative conservation law, that of conservation of energy, can also be used. However, the details of how mass is transferred from species to species is better understood than corresponding energy transformations. The mass interactions relate among other factors to the kinetics of the populations and it is to this that the majority of the paper is devoted to exploring.

Humic Substances in Natural Waters and Their Complexation with Trace Metals and Radionuclides: A Review

Boggs, Sam Jr.; Livermore, David; Seitz, Martin G.
Fonte: Universidade de Delaware Publicador: Universidade de Delaware
Tipo: Relatório Formato: 7323045 bytes; application/pdf
Português
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Dissolved humic substances (humic and fulvic acids) occur in surface waters and groundwaters in concentrations ranging from less than 1 mg(C)/L to more than 100 rng(C)/L. Humic substances are strong complexing agents for many trace metals in the environment and are also capable of forming stable soluble complexes or chelates with radionuclides. Concentrations of humic materials as low as 1 mg(C)/L can produce a detectable increase in the mobility of some actinide elements by forming soluble complexes that inhibit sorption of the radionuclides onto rock materials. The stability of trace metal- or radionuclide-organic complexes is commonly measured by an empirically determined conditional stability constant (K'), which is based on the ratio of complexed metal (radionuclide)in solution to the product concentration of uncomplexed metal and humic complexant. Larger values of stability constants indicate greater complex stability.