Tesis: "Diffusive gradients in thin films"

1

Altier, Infantes Alexandra. "Diffusive Gradients in Thin-films (DGT) beyond perfect-sink conditions". Doctoral thesis, Universitat de Lleida, 2018. http://hdl.handle.net/10803/585874.

Texto completo

Resumen

La presencia d'elements metàl•lics en el medi ambient està fortament influenciada per les activitats antropogèniques entre les que emergeix l'ús de nous materials basats en nanopartícules metàl•liques i òxids metàl•lics. L'especiació d'ions metàl•lics juga un paper fonamental en la determinació de la biodisponibilitat, l’ecotoxicitat i en general en la seva circulació en mitjans naturals. Però la disponibilitat d'elements metàl•lics i les propietats tòxiques o nutritives depenen a mès d’un conjunt de processos fisicoquímics de caràcter dinàmic, on les condicions d'equilibri, malgrat el seu ampli ús, representen només un cas límit. La finalitat d'aquest treball ha estat la mesura dels fluxos de metalls a diferents escales de temps i espai mitjançant la tècnica analítica dinàmica DGT (Diffusive Gradient in Thin-films) així com el desenvolupament de models fisicoquímics adequats per a la interpretació dels resultats. El marc interpretatiu dels resultats DGT s'ha completat amb la inclusió d'efectes escassament descrits en la literatura recent, com ara la influència dels efectes de competició, d’equilibri o de saturació de la resina a més dels fenòmens electrostàtics a baixes forces iòniques. Es presenten expressions aproximades simples per a l'anàlisi d'aquests fenòmens, així com la seva aplicació a sistemes experimentals que permeten observar la seva bondat. Un cop abordat el treball de sistemes simples amb només ions metàl•lics, s'han estudiat sistemes amb un únic lligand i sistemes amb mescles de lligands. Amb aquests sistemes s'ha analitzat fins a quin punt la contribució dels complexos a la disponibilitat depèn de la composició del sistema, tot corroborant que mesures en sistemes amb un únic complex serveixen per predir el comportament de les mescles. A causa de les variacions espacials i temporals que poden patir les concentrations dels ions metàl•lics en aigües naturals, l'última part de l'estudi s'ha centrat en avaluar la capacitat de resposta de la tècnica DGT per mesurar fluctuacions en la concentració. Aquest estudi ha demostrat que a més de proporcionar concentracions mitjanes amb el temps en condicions relativament simples, aquesta tècnica és capaç de determinar concentracions representatives en una àmplia gamma de condicions naturals.
La presencia de elementos metálicos en el medio ambiente está fuertemente influenciada por actividades antropogénicas entre las que emerge el uso de nuevos materiales basados en nanopartículas metálicas y óxidos metálicos. La disponibilidad de elementos metálicos y sus propiedades tóxicas o nutritivas están determinadas por un conjunto de procesos físico-químicos de carácter dinámico, donde la especiación en condiciones de equilibrio, a pesar de su amplio uso, representa sólo un caso límite. La finalidad de este trabajo ha sido la medida de los flujos de metales disponibles a diferentes escalas de tiempo y espacio mediante la técnica analítica dinámica DGT (Diffusive Gradient in Thin-films) así como el desarrollo de modelos fisicoquímicos adecuados para la interpretación de los resultados. El marco interpretativo de los resultados DGT se ha completado con la inclusión de efectos escasamente descritos en la literatura reciente, tales como la influencia de los efectos de competición, equilibrio o saturación de la resina además de la relevancia de los fenómenos electrostáticos a bajas fuerzas iónicas. Se presenta el análisis de estos fenómenos, con expresiones analíticas aproximadas deducidas a partir de la formulación del problema y se aplican a sistemas experimentales para observar la validez de dichas aproximaciones. Una vez abordado el trabajo de sistemas simples con sólo iones metálicos, se han estudiado sistemas con un único ligando y sistemas con mezclas de ligandos. Con estos sistemas se ha analizado hasta qué punto la contribución de los complejos a la disponibilidad depende de la composición del sistema, corroborándose que medidas del grado de labilidad en sistemas con un único complejo pueden predecir el flujo en las mezclas. Se reportan los mecanismos fisicoquímicos que describen la influencia del efecto mezcla sobre el grado de labilidad de un complejo determinado. Debido a las variaciones espaciales y temporales que pueden sufrir los iones metálicos en aguas naturales, la última parte del estudio se ha centrado en evaluar la capacidad de respuesta de la técnica DGT para medir fluctuaciones en la concentración. Este estudio ha demostrado que además de proporcionar concentraciones promediadas con el tiempo en condiciones relativamente simples, esta técnica es capaz de determinar concentraciones representativas en una amplia gama de condiciones naturales.
The presence of heavy metals in the environment is strongly influenced by anthropogenic activities due to the emerging use of new materials based on metallic nanoparticles or metal oxides. The speciation of metal ions plays a fundamental role in the determination of bioavailability, ecotoxicity and in general in its circulation in natural media. The availability of metal ions and their toxic or nutritive properties are determined by a set of physical-chemical processes, where equilibrium conditions, despite its widespread use, only represent a limiting case. The aim of this work was to measure the flux of available metals at different time and space scales through the dynamic analytical technique DGT (Diffusive Gradient in Thin-films). The interpretative framework of the DGT results has also been completed with the inclusion of effects scarcely described in the recent literature, such as the influence of competition, saturation of the resin sites, kinetic effects in the binding of the target analyte to the resin domain or the relevance of electrostatic phenomena at low ionic strengths. Approximate analytical expressions were deduced from the basic formulation and applied to experimental systems to check the agreement with the experimental accumulations. Once the study of simple systems with only metal ions has been addressed, systems with a single ligand or systems with a mixture of complexes have been studied. These systems were analyzed to test if the composition of the system modifies the availability of the complexes. As a conclusion of this work, it was shown that the lability degree of complexes measured in single ligand systems can be used to approximately predict the accumulation in mixtures. A physicochemical explanation of the mechanism by which the lability of a complex changes in a mixture was reported. Since spatial and temporal variations in metal concentrations are common in natural waters, the last part of this study has focused on the assessment of the response capabilities of the DGT technique to measure concentration fluctuations. This study has shown that besides it provides time-weighted average concentrations over time for relatively simple conditions, this technique is able to determine accurate and representative metal concentrations in a wide range of natural conditions.

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

Kobayashi, Takahiro. "Development and application of the DGT technique for the measurement of nitrate, ammonia and phosphate in natural waters, sediments and soils". Thesis, Lancaster University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302435.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Luo, Jun. "Effect of soil dynamics on metal uptake by plants and diffusive gradients in thin-films". Thesis, Lancaster University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533063.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Cole, Russell Francis. "Determination of organotin compounds in coastal sediment pore-water by diffusive gradients in thin-films (DGT) technique". Thesis, University of Portsmouth, 2016. https://researchportal.port.ac.uk/portal/en/theses/determination-of-organotin-compounds-in-coastal-sediment-porewater-by-diffusive-gradients-in-thinfilms-dgt-technique(f452f268-d8c7-4ca9-acb3-ffd6fb733f8e).html.

Texto completo

Resumen

Organotin compounds still present a high risk to biota in the aquatic environment. Measuring the behaviour of the freely dissolved fractions of these compounds in sediment compartments is challenging, with costly and sensitive analytical techniques required for their measurement. Diffusive gradients in thin-films (DGT) allow for the uptake and pre-concentration of analytes in a binding gel and is used to measure dissolved metals and some organic compounds. The utility of novel silica-bound sorbents (C8, C18, mixed phases) as DGT binding gels for the sequestration of organotins in the marine environment was the primary focus of work in this project. The C8 sorbent showed the optimum performance in the uptake and recovery of organotins across pH, ionic strength and in filtered sea water. It was used subsequently as the binding layer in DGT sediment devices (160 mm × 34 mm) overlaid with a mixed-cellulose ester membrane (0.45 μm) as the single diffusion layer. These were used to investigate pore water mobilisation and concentrations of organotins in coastal sediment cores collected from a contaminated site. Organotins demonstrated a non-sustained uptake scenario, with DGT flux and freely dissolved concentrations in pore water measured to decline at 1 cm depth intervals over deployments of 2-28 days. Using time series, concentrations in pore water at t = 0 were calculated providing empirical pore water depletion curves for sediment cores. Using standard laboratory instrumentation (i.e. gas chromatography-mass spectrometry) low limits of detection were achieved (TBT = 0.4 ng L^-1 after 2 weeks of sampling).

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Lindfors, Sarah. "Metal Fractionation in Snowmelt Runoff : A Comparison between Ultrafiltration and Diffusive Gradients in Thin Films (DGT) techniques". Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65018.

Texto completo

Resumen

Urban runoff is a non-point pollution source deteriorating water quality of natural watersystems. The composition of urban runoff vary depending on land use, seasonal changes anddifferent surfaces that come into contact with the water. Urban runoff often contain metals andAl, Cd, Cr, Cu, Fe, Ni, Pb and Zn are of particular concern for the environment due to theirpotential toxicity. Metals in runoff can be present in different phases, associated with particles,colloids of different sizes or dissolved in the free phase. The different phases vary in size butalso overlap each other. Information about metal phases and species in runoff is essential tounderstanding metal transport and design runoff treatment systems.Membrane filtration followed by ultrafiltration is an established technique to distinguish theparticulate, colloidal and truly dissolved fractions. However, the “truly dissolved” fraction mayconstitute of the free phase, colloidal phase or both of them since the technique onlydiscriminates by size. Diffusive gradients in thin films (DGT) is a relatively new technique thatmeasures the labile fraction, sometimes referred to as the most bioavailable fraction. The labilefraction includes free metal ions and small complexes available to diffuse through a diffusivelayer under a reasonable period of time. Kinetically inert species are discriminated.The scope of this thesis was to investigate metal fractionation in snowmelt runoff from differenturban surfaces using two techniques, ultrafiltration and DGT. An additional aim was to studythe speciation described by the two techniques in the different types of runoff. Two types ofrunoff were sampled to conduct measurements on. Runoff from well-defined catchments (anindustrial area and a parking lot) and roof runoff from two roofing materials (zinc and coppersheet). In total, four runoff samples were membrane filtrated (pore size 0.45 μm) followed byeither ultrafiltration (delimiting 3 kNMWL) or DGT measurements in the laboratory. Analysisof metals was conducted in all steps and pH, electric conductivity, total suspended solids andtotal organic carbon was measured in the untreated samples.The results show that metal concentrations were generally higher in the catchment runoffcompared to the roof runoff with few exceptions, Cu and Pb from copper roof and Zn from zincroof. Regarding fractionation, the two types of runoff showed similarities when it came tometals mainly bound to particles. The metals that were abundant in several phases showeddifferent fractionations between the catchment runoff and the roof runoff. The metals releasedin roof runoff was to a higher extent found as free ions compared with the catchment runoff. Adiscussion was held about the different metal fractions and treatment possibilities. Comparingthe two techniques, the DGT measurements could be used to further interpret the results fromthe ultrafiltration regarding the colloidal and free phase.
Dagvatten är en diffus föroreningskälla som försämrar vattenkvalitén hos naturliga vattendrag.Samansättningen av föroreningar i dagvatten kan variera beroende på markanvändning,årstidsvariationer och de olika ytor som dagvattnet kommer i kontakt med. Dagvatten innehållerofta metaller och Al, Cd, Cr, Cu, Fe, Ni, Pb och Zn kan vara toxiska för miljön i högakoncentrationer. Metaller i dagvatten kan förekomma i olika faser beroende på om de är bundnamed partiklar, kolloider av olika storlek eller om de är i löst fas. De olika faserna varierar istorlek men överlappar även varandra något. Kunskap om de olika faserna är viktigt förförståelsen om metallernas transportmekanismer och för att kunna designa eller förbättrareningssystem.Membranfiltrering följt av ultrafiltrering är en etablerad teknik för att särskilja partikulärtmaterial, kolloider och den sanna lösta fraktionen. Dock så kan den ”sanna lösta” fraktioneninnehålla antingen den kolloidala fasen, lösta fasen eller båda två eftersom tekniken baseras påstorleksfördelning. DGT (på engelska diffusive gradients in thin films) är en relativt ny tekniksom mäter den labila fraktionen som ibland benämns som den mest biotillgängliga fraktionen.Den labila fraktionen inkluderar fria metalljoner men även små komplex som kan diffunderagenom en diffusionsgel under en rimlig tidsperiod. Species som är kinetisk inerta kommer intemätas.Syftet med detta arbete var att undersöka metallfraktionering i snösmälts-avrinning från olikaurbana ytor genom att använda två tekniker, ultrafiltrering och DGT. Ett delmål var även attgranska de species som beskrevs av de två teknikerna i de olika typerna av dagvatten. Två olikaslags dagvatten samlades in och undersöktes. Dagvatten från väldefinierade avrinningsområden(ett industriområde och en parkeringsplats) och takavrinning från två takmaterial (zink- ochkopparplåtar). Totalt fyra dagvattenprover genomgick membranfiltrering (porstorlek 0,45 μm)följt av antingen ultrafiltrering (avgränsning 3 kNMWL) eller DGT mätningar i laboratoriet.Metallanalyser genomfördes i alla steg och pH, konduktivitet, suspenderade partiklar ochorganiskt kol mättes på det obehandlade proverna.Resultaten visade att de uppmätta metallkoncentrationerna var generellt högre i takavrinningenjämfört med dagvattnet från de hela avrinningsområdena. Dock med några undantag, Cu ochPb från koppartak och Zn från zinktak. När det kom till fraktionering fanns det likheter mellanavrinning från hela områden och från taken beträffande de metaller som till största del varbundna till partiklar. Däremot var det skillnad mellan de olika avrinningstyperna gällandefraktionering av metallerna som förekom i flera av faserna. I takavrinningen fanns det i störreutsträckning metaller som fria joner jämfört med avrinningsområdena. En slutsats var att DGTmätningarna kunde användas till att tolka resultaten från ultrafiltreringen när det gälldekolloidala och fria faserna.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Bennett, William W. "Development of the Diffusive Gradients in Thin Films Technique for the Measurement of Inorganic Arsenic Speciation in Water and the Investigation of Arsenic Sediment Biogeochemistry". Thesis, Griffith University, 2012. http://hdl.handle.net/10072/365634.

Texto completo

Resumen

A novel diffusive gradients in thin films (DGT) technique for the measurement of inorganic arsenic speciation in situ was developed and evaluated. In addition, a diffusive equilibration in thin films (DET) technique was optimized for the high-resolution, colorimetric measurement of iron(II) in sediment porewaters. These techniques were then utilized to investigate processes of arsenic mobilization in sediments and the effect of changing redox conditions on the cycling of arsenic in freshwater and marine sediments. A titanium dioxide-based adsorbent, Metsorb™, was evaluated as a DGT adsorbent for measuring total inorganic arsenic (AsIII and AsV), as well as selenite (SeIV). Performance characteristics such as diffusion coefficients, linear accumulation over time, the effect of pH and ionic strength, and the capacity of the adsorbent were tested and found to be acceptable. The method was also evaluated in the field and found to accurately and precisely measure environmentally relevant arsenic concentrations. The speciation of inorganic arsenic was achieved by developing a second DGT technique that selectively measured AsIII in the presence of AsV. This new technique utilized a mercaptopropylfunctionalized silica gel as a selective adsorbent for AsIII, allowing the speciation of total inorganic arsenic to be calculated by deploying both sampler types simultaneously and calculating the AsV concentration by difference. This new approach to in situ arsenic speciation was successfully evaluated at a variety of pH levels and ionic strengths, and in the challenging matrix of seawater. The newly developed DGT techniques for arsenic speciation were applied to the investigation of arsenic mobility in sediments. To aid in this, a recently described colorimetric DET technique was optimized for the measurement of iron(II) concentrations in sediment porewater. The diffusive gel located at the front of the DGT samplers was utilized as the DET gel for colorimetric analysis of iron(II), enabling co-distributions of these analytes to be measured in situ. The combined DET – DGT approach was applied to freshwater, estuarine and marine sediment mesocosms to investigate the relationship between the reductive dissolution of iron(III) (hydr)oxide minerals and the release of arsenic to sediment porewaters. The effect of induced anoxia and subsequent reoxygenation on arsenic and iron cycling within freshwater and marine sediments was also investigated using sediment mesocosm incubations and the newly developed DET and DGT techniques. These techniques, used in conjunction with sediment mesocosms, proved to be a powerful new approach for the investigation of arsenic biogeochemistry and the mechanisms of arsenic mobilization in the environment.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

Li, Weijia y n/a. "Development of New Binding Phases for Speciation Measurements of Trace Metals with the Diffusive Gradients in Thin Films Technique". Griffith University. School of Environmental and Applied Science, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040504.150905.

Texto completo

Resumen

The recently developed technique of diffusive gradients in thin films (DGT) for speciation measurement of analytes in the environment was further developed through the development of series of new binding phases including poly(acrylamide-co-acrylic acid) copolymer hydrogel (PAM-PAA), poly(acrylamidoglycolic acid-co-acrylamide) (PAAGA-PAM) hydrogel, the Whatman P81 cellulose phosphate ion exchange membrane (P81) and a liquid binding phase of poly(4-styrenesulfonate) (PSS). A new diffusion layer, cellulose dialysis membrane, was also employed for the liquid binding phase DGT. PAM-PAA copolymer hydrogel was prepared by the controlled hydrolysis of polyacrylamide (PAM) in an alkaline solution of 10% sodium hydroxide. The capacity of the copolymer hydrogel to bind various metal ions was tested under a range of uptake conditions. Ions such as Cu2+ and Cd2+ were bound more strongly to the copolymer hydrogel than the competing ions such as Na+, K+, Ca2+ and Mg2+. Metals bound to the copolymer hydrogel can be efficiently eluted in 2 M HNO3 solution (>94%). Application of this new binding material to DGT technique was validated in a synthetic lake water (Windermere, Lake District, UK) with a recovery of 99.0% for Cu2+. PAAGA-PAM hydrogel was prepared by copolymerising 2-acrylamidoglycolic acid with acrylamide. The metal ion binding properties of the hydrogel were characterised for Cu2+, Cd2+ and competing ions under various experimental conditions. The hydrogel was shown to bind Cu2+ and Cd2+ strongly under non-competitive binding conditions, with binding capacities of 5.3 and 5.1 micromol cm-2, respectively. The binding capacity of each metal decreased, under competitive binding conditions (with a range of metal ions present at 17.8 mN), to 1.3 and 0.17 micromol cm-2, respectively, indicating a strong selective binding towards Cu2+. The metal ions were readily recovered (>94%) by eluting with 2 M HNO3. Finally, the copolymer hydrogel was tested as a binding phase with the DGT technique. A linear mass vs. time relationship was observed for Cu2+ in Windermere water with a recovery of close to 100%. The use of a commercially available solid ion exchange membrane (P81) as the binding phase in DGT analysis was demonstrated. P81 is a strong cation exchange membrane. Its performance characteristics as a new binding phase in DGT measurement of Cu2+ and Cd2+ were systematically investigated. Several advantages over the conventional ion exchange resin-embedded hydrogel based binding phases used in DGT were observed. These include: simple preparation, ease of handling, and reusability. The binding phase preferentially binds to transition metal ions rather than competing ions. Within the optimum pH range (pH 4.0 - 9.0), the maximum non-competitive binding capacities of the membrane for Cu2+ and Cd2+ were 3.22 and 3.07 micromol cm-2, respectively. The suitability of the new membrane-based binding phase for DGT applications was validated experimentally. The results demonstrated excellent agreement with theoretically predicted trends. The reusability of this binding phase was also investigated. Application of a liquid binding phase and a dialysis membrane diffusive layer were proposed for the first time. The binding phase was a 0.020 M solution of poly(4-styrenesulfonate) (PSS) polyelectrolyte using a specially designed DGT device. The binding properties of Cd2+, Cu2+, and a range of alkali and alkaline earth metal ions to the PSS solution were characterised. The PSS behaved like a cation exchanger with preferential binding to Cd2+ (6.0 micromole ml-1, log K = 9.0) and Cu2+ (2.5 micromole ml-1, log K = 8.1) under competitive binding conditions. The DGT devices were successfully validated for Cd2+ and Cu2+ in Windermere water. The speciation performance of the solid and liquid binding phases developed in this study was investigated in solutions containing ethylenediaminetetraacetic acid disodium salt (EDTA), humic acid (HA), glucose (GL), dodecylbenzenesulfonic acid (DBS) and tannic acid (TA) with Cu2+ and Cd2+. The ratios of labile metals over total metals were at good agreement with calculated theoretical values using Stability Constants Database. The results indicated that the DGT-labile concentration measured by DGT with these binding phases is essentially free metal ion concentration in the sample. All newly developed DGT binding phases were successfully applied for environmental speciation. The field deployments were carried out in both freshwater and salt-water test sites.

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

Li, Weijia. "Development of New Binding Phases for Speciation Measurements of Trace Metals with the Diffusive Gradients in Thin Films Technique". Thesis, Griffith University, 2004. http://hdl.handle.net/10072/367741.

Texto completo

Resumen

The recently developed technique of diffusive gradients in thin films (DGT) for speciation measurement of analytes in the environment was further developed through the development of series of new binding phases including poly(acrylamide-co-acrylic acid) copolymer hydrogel (PAM-PAA), poly(acrylamidoglycolic acid-co-acrylamide) (PAAGA-PAM) hydrogel, the Whatman P81 cellulose phosphate ion exchange membrane (P81) and a liquid binding phase of poly(4-styrenesulfonate) (PSS). A new diffusion layer, cellulose dialysis membrane, was also employed for the liquid binding phase DGT. PAM-PAA copolymer hydrogel was prepared by the controlled hydrolysis of polyacrylamide (PAM) in an alkaline solution of 10% sodium hydroxide. The capacity of the copolymer hydrogel to bind various metal ions was tested under a range of uptake conditions. Ions such as Cu2+ and Cd2+ were bound more strongly to the copolymer hydrogel than the competing ions such as Na+, K+, Ca2+ and Mg2+. Metals bound to the copolymer hydrogel can be efficiently eluted in 2 M HNO3 solution (>94%). Application of this new binding material to DGT technique was validated in a synthetic lake water (Windermere, Lake District, UK) with a recovery of 99.0% for Cu2+. PAAGA-PAM hydrogel was prepared by copolymerising 2-acrylamidoglycolic acid with acrylamide. The metal ion binding properties of the hydrogel were characterised for Cu2+, Cd2+ and competing ions under various experimental conditions. The hydrogel was shown to bind Cu2+ and Cd2+ strongly under non-competitive binding conditions, with binding capacities of 5.3 and 5.1 micromol cm-2, respectively. The binding capacity of each metal decreased, under competitive binding conditions (with a range of metal ions present at 17.8 mN), to 1.3 and 0.17 micromol cm-2, respectively, indicating a strong selective binding towards Cu2+. The metal ions were readily recovered (>94%) by eluting with 2 M HNO3. Finally, the copolymer hydrogel was tested as a binding phase with the DGT technique. A linear mass vs. time relationship was observed for Cu2+ in Windermere water with a recovery of close to 100%. The use of a commercially available solid ion exchange membrane (P81) as the binding phase in DGT analysis was demonstrated. P81 is a strong cation exchange membrane. Its performance characteristics as a new binding phase in DGT measurement of Cu2+ and Cd2+ were systematically investigated. Several advantages over the conventional ion exchange resin-embedded hydrogel based binding phases used in DGT were observed. These include: simple preparation, ease of handling, and reusability. The binding phase preferentially binds to transition metal ions rather than competing ions. Within the optimum pH range (pH 4.0 - 9.0), the maximum non-competitive binding capacities of the membrane for Cu2+ and Cd2+ were 3.22 and 3.07 micromol cm-2, respectively. The suitability of the new membrane-based binding phase for DGT applications was validated experimentally. The results demonstrated excellent agreement with theoretically predicted trends. The reusability of this binding phase was also investigated. Application of a liquid binding phase and a dialysis membrane diffusive layer were proposed for the first time. The binding phase was a 0.020 M solution of poly(4-styrenesulfonate) (PSS) polyelectrolyte using a specially designed DGT device. The binding properties of Cd2+, Cu2+, and a range of alkali and alkaline earth metal ions to the PSS solution were characterised. The PSS behaved like a cation exchanger with preferential binding to Cd2+ (6.0 micromole ml-1, log K = 9.0) and Cu2+ (2.5 micromole ml-1, log K = 8.1) under competitive binding conditions. The DGT devices were successfully validated for Cd2+ and Cu2+ in Windermere water. The speciation performance of the solid and liquid binding phases developed in this study was investigated in solutions containing ethylenediaminetetraacetic acid disodium salt (EDTA), humic acid (HA), glucose (GL), dodecylbenzenesulfonic acid (DBS) and tannic acid (TA) with Cu2+ and Cd2+. The ratios of labile metals over total metals were at good agreement with calculated theoretical values using Stability Constants Database. The results indicated that the DGT-labile concentration measured by DGT with these binding phases is essentially free metal ion concentration in the sample. All newly developed DGT binding phases were successfully applied for environmental speciation. The field deployments were carried out in both freshwater and salt-water test sites.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental and Applied Science
Full Text

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

Köhler, Sandra. "Bestimmung der Bioverfügbarkeit von Kupfer und Zink in Böden mit der Methode DGT (diffusive gradients in thin films)". Zürich : ETH, Eidgenössische Technische Hochschule Zürich, Institut für terrestrische Ökologie, 2002. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=102.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Kane, David. "Evaluating phosphorus availability in soils receiving organic amendment application using the Diffusive Gradients in Thin-films (DGT) technique". Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8001.

Texto completo

Resumen

Phosphorus is a resource in finite supply. Use of organic amendments in agriculture can be a sustainable alternative to inorganic P, provided it can meet crop requirements. However a lack of consistent knowledge of plant P availability following application of organic amendments, limits its potential. Studies suggest chemical extraction procedures, may not reflect plant available P. The Diffusive Gradients in Thin-films (DGT) technique is based on natural diffusion of P via a hydrogel and sorption to a ferrihydrite binding layer; which should accurately represent soil P (CDGT) in a plant available form. The aim of this research was to evaluate changes in soil P availability, following the addition of organic amendments, cattle farmyard manure (FYM), green waste compost (GW), cattle slurry (SLRY) and superphosphate (SP) using Olsen P and DGT. The research included incubation, and glasshouse studies, using ryegrass (Lolium perenne L.). Soils with a history of application of the aforementioned organic amendments were used (Gleadthorpe), as well as a soil deficient in P (Kincraigie). The hypotheses were as follows H1 A build-up of P available by diffusive supply, from historic treatment additions and subsequent availability from fresh treatment additions will be demonstrated by DGT. H2 Historical treatment additions are more important at determining yield and P uptake than fresh additions. H3 DGT can detect changes in P available by diffusive supply following addition of different treatments and subsequently following lysis of microbial cells on a soil deficient in P. H4 DGT will provide a more accurate indication of plant P availability than organic amendments in a soil deficient in P. H5 P measurements using DGT will be lower from organic amendments than superphosphate.H6 DIFS simulations of soil kinetic parameters will provide additional information about how treatments influence P resupply from solid phase to solution following DGT deployment. Cont/d.

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Huang, Jianyin. "Development and Evaluation of the Diffusive Gradients in Thin Films (DGT) Techniques for the Measurement of Nutrient Concentrations in Natural Waters". Thesis, Griffith University, 2016. http://hdl.handle.net/10072/367045.

Texto completo

Resumen

Due to rapid industrialisation, the growing global population, and the impacts of climate change, the availability and quality of water resources around the world has become degraded. Some regions are suffering water shortages despite sufficient water reserves, because surface and ground waters are contaminated to such a degree that they have become inadequate for potable use. Agricultural practices, industrial discharges and human wastewater are responsible for most contamination of water. Nitrogen (ammonium, nitrate and nitrite) and phosphorus (phosphate) are the most common nutrients in freshwaters and estuaries that impact water quality. Excess nutrient loadings to water bodies can affect many aquatic organisms and, ultimately, contribute to the degradation of freshwater, estuarine and coastal marine ecosystems. Furthermore, high concentrations of nutrients in drinking water sources can cause health impacts to human beings. Due to the potential sporadic nature of the contamination sources, grab sampling may fail to identify contamination events. Nutrient loadings to waterways from point and non-point sources are of major ecological concern and represent one of the most significant water quality issues in surface water bodies, and hence require use of accurate and representative approaches to monitor nutrient concentrations. DGT as diffusive gradients in thin films, a well-established passive sampling technique, allows determination of time-weighted average measurements over environmentally relevant time-scales.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Turner, Geraldine Sarah Clinton. "The application of the passive sampling technique diffusive gradients in thin-films (DGT) to the measurement of uranium in natural waters". Thesis, University of Portsmouth, 2013. https://researchportal.port.ac.uk/portal/en/theses/the-application-of-the-passive-sampling-technique-diffusive-gradients-in-thinfilms-dgt-to-the-measurement-of-uranium-in-natural-waters(107c3ce9-2c00-435f-b241-0b668c36bf9b).html.

Texto completo

Resumen

This thesis describes the application of a passive sampler, Diffusive Gradient in Thin Films (DGT), to the measurement of uranium in natural waters. Four resins (Chelex-100, manganese dioxide [MnO2], Diphonix® and MetsorbTM) were trialled with the DGT device. In freshwater environments, the MetsorbTM accumulated uranium in line with the DGT equation for 7 d with an acuracy of 75%; Chelex-100 did not accumulate uranium past 2 d; MnO2 accumulated up to 75% of that predicted by the DGT equation for 4 d; and the Diphonix® accumulated uranium for 7 d with an accuracy of ~100%. None of the resins tested in this study accumulated uranium in a marine setting in line with DGT predicted values past 2 d. The application of DGT to regulatory environmental monitoring schemes was investigated with MetsorbTM. The MetsorbTM DGT devices were deployed for 7 days at a time over a 6 month period at two freshwater field sites. Fluctuations in water chemistry were monitored and the size of the diffusive boundary layer (DBL) was measured. The uranium accumulated by the MetsorbTM DGT showed close agreement with the grab samples. The size of the DBL was found to be significant, particularly in low flow conditions. This study showed that DGT could be used as a tool to both monitor radioncludes in the environment, and to obtain information on the speciation and organic interactions. The lability of uranium-humic acid complexes was also examined in this study. Initial data shows that the uranyl-humic complex is labile in low pH environments, but becomes increasingly kinetically limited the higher the pH and the higher the humic acid:uranium ratio. Data is also presented on the penetration parameter of the uranyl ion into the resin gel layer, and how this can be used to indicate lability. Lability is important in determining bioavailability and potential toxicity of uranium.

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Österlund, Helene. "Further characterisation and applications of the diffusive gradients in thin films technique : In situ measurements of anions and cations in environmental waters". Doctoral thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17418.

Texto completo

Resumen

As both the toxicity and the mobility of trace elements are related to chemical forms present, robust methods for element speciation analysis are of great interest. During the last 15 years, hundreds of scientific articles have been published on the development and applications of the diffusive gradients in thin films (DGT) passive sampling technique. The aim of this thesis was to explore new application areas as well as carry out further characterisation of DGT-adsorbents already on the market. The commercially available DGT containing ferrihydrite adsorbent, currently in use for the determination of phosphate and inorganic arsenic, was characterised with respect to anionic arsenate, molybdate, antimonate, vanadate and tungstate determination. Tests were performed in the laboratory as well as in the field. Diffusion coefficients were determined for the anions using two different methods with good agreement. Simultaneous measurements of arsenate were conducted as quality control to facilitate comparison of the performance with previous work. The ferrihydrite-backed DGT was concluded useful for application over the pH-range 4 to 10 for vanadate and tungstate, and 4 to <8 for molybdate and antimonate. At pH values ≥8, deteriorating adsorption was observed. Further investigations of the ferrihydrite-DGT device were done with respect to organic arsenic species. From previous research it is understood that the two most prevalent forms of organic arsenic in natural waters, monomethylarsinate (MMA) and dimethylarsonate (DMA), adsorb to ferrihydrite. It was concluded that MMA and under some conditions DMA are accumulated and might therefore be included in total arsenic measurements. A method for speciation of inorganic As, DMA and MMA was described. DGT sampling was applied at three stations, with different salinities, in the brackish Baltic Sea. Time series as well as vertical profiles were taken and complementary membrane- (<0.22 μm) and ultrafiltrations (<1 kDa) were conducted on discrete samples collected at 5 m depth. A combination of a restricted pore (RP) version of DGT and the normal open pore (OP) DGT, both loaded with Chelex cation exchanger, was used for speciation of copper and nickel. Due to minimal differences in results between the OP- and RP-DGTs it was suggested that the complexes were smaller than the pore size of the RP gel (~1 nm) resulting in both DGTs accumulating essentially the same fraction. Furthermore, there seemed to be a trend in copper speciation indicating a higher degree of strong complexation with increasing salinity. The low salinity stations are more impacted by fluvial inputs which will likely affect the nature and composition of the organic ligands present. Assuming that copper forms more stable complexes with ligands of marine rather than terrestrial origin would be sufficient to explain the observed trend. Additionally, uranium results from the same sampling tours were used to evaluate OP-DGT for in situ uranium measurements. Previous research has focused on laboratory studies for characterisation of a range of suitable uranium adsorbents, including Chelex. From the Baltic Sea study, a strong correlation between DGT-labile uranium and pH was revealed. The correlation could not be associated to organic complexation, since the ultrafiltration results implicated that uranium was truly dissolved. Instead it must be attributed to the formation of stable inorganic anionic uranyl-carbonate complexes, the stability of which increases with increasing numbers of carbonates and pH. Transplanted aquatic moss has commonly been used to monitor bioavailable trace metal contaminations in freshwater. Like the DGT technique the method has the advantage of generating time-weighted averaged concentrations. The DGT technique has in several previous studies been suggested to mimic biological uptake of trace metals. Four speciation/fractionation techniques – DGT, transplanted aquatic moss, ultrafiltration (1 kDa) and membrane filtration (0.22 μm) – were used in parallel for measurements of Al, Cd, Co, Cu, Fe, Mn, Ni and Zn in a contaminated freshwater stream in northern Sweden. Differences and similarities between the methods were investigated and how these depend on geochemical water quality. Strong correlations between DGT-results and the concentrations in the filtrate (<0.22 μm) and ultrafiltration permeate for Al, Cu, Cd, Co and Zn were detected and, generally, elevated trace metal concentrations were found in the transplanted moss, compared to moss from the non-polluted reference stream. However, no correlation between moss and DGT-labile concentrations could be discerned.
Godkänd; 2011; 20110921 (helost)

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Panther, Jared Graeme. "Diffusive Gradients in Thin Films for Inorganic Arsenic Speciation and Electrothermal Atomic Absorption Spectrometry with a Coupled Microcolumn for Trace Metal Speciation". Thesis, University of Canterbury. Chemistry, 2008. http://hdl.handle.net/10092/3675.

Texto completo

Resumen

This thesis is directed towards the development of the diffusive gradients in thin films (DGT) technique for the measurement of total dissolved As, and for As speciation measurements. In addition, a preliminary investigation of a novel laboratory-based method for measuring labile metal species was carried out; this method involved the coupling of a microcolumn of adsorbent with a standard electrothermal atomic absorption spectrometer. An iron-oxide adsorbent was utilized for As measurements by DGT. The diffusion coefficients of inorganic Asv and AsIII> were measured through the polyacrylamide diffusive gel using both a diffusion cell and DGT devices. A variety of factors that may affect the measurement of total As by DGT were investigated. These factors, which included pH, anions, cations, fulvic acid, FeIII-fulvic acid complexes, and colloidal Fe, may affect the adsorption of the As species to the iron-oxide, or may affect the diffusion coefficients of the individual As species. The DGT method was further developed to selectively accumulate the AsIII species in the presence of Asv. This was achieved by the placement of a negatively charged Nafion membrane at the front of the DGT device which slowed the diffusion of the negatively charged Asv species (H₂AsO₄₂ ⁻) considerably, relative to the uncharged AsIII species (H₃AsO₃). The effect that pH, anions, and cations may have on the selective accumulation of AsIII, in the presence of Asv, was investigated. DGT devices without a Nafion membrane and with a Nafion membrane were deployed in natural waters to determine the total inorganic As and AsIII> concentrations, and to evaluate its performance. A preliminary investigation of the coupling of a microcolumn of Chelex-100 resin with a standard electrothermal atomic absorption spectrometer was undertaken to establish its value as a laboratory-based speciation method. This involved the examination of various microcolumn materials to accommodate the Chelex-100 resin, and finding an appropriate buffer that could be used to buffer the Chelex-100 resin without interfering with the ETAAS measurement. Furthermore, factors that may affect the uptake of metal by the Chelex-100 resin, such as concentration of buffer in solution, ionic strength, and conditioning of the Chelex-100 resin, were investigated.

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Bořek, Tomáš. "Toxické kovy ve vodě a sedimentech vodní nádrže Brno". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2009. http://www.nusl.cz/ntk/nusl-216543.

Texto completo

Resumen

Diploma thesis deals with usage of the diffusive gradients in thin films technique (DGT) for the determination of labile metal species in the surface water and sediments of Brno water reservoir. Sediment and water samples were collected on the selected sides of Brno water reservoir on September and October 2008. The DGT technique was used for determination of depth profiles of Fe, Mn, Pb, Cd, Zn, Cu, Ni and Al. The DGT probes with three different thicknesses of diffusive layer were applied into the sediment samples. The obtained results gave the information about release of metals from solid phase into the pore water of sediment. The concentrations of Fe, Mn, Pb and Cd in sediments were determined by atomic absorption spectrometry after microwave decomposition. The DGT technique was used also for determination of Fe, Mn, Pb and Cd in surface water from Brno water reservoir.

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

Shiva, Amir Houshang. "Evaluating the Performance of DGT Technique for Selective Measurement of Trace Metals and Assessment of Environmental Health in Coastal Waters". Thesis, Griffith University, 2016. http://hdl.handle.net/10072/367257.

Texto completo

Resumen

The diffusive gradients in thin films (DGT) technique as a passive sampler for measurement of trace metals was validated and evaluated. A systematic determination of diffusion coefficients for a wide range of cationic (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and oxyanionic (Al, As, Mo, Sb, V, W) metals in open (ODL) and restricted (RDL) diffusive layers used by the DGT technique was performed. The diffusion coefficients were determined at acidic and neutral pH, using two independent methods, diffusion cells and time-series DGT techniques. The calculated values for many oxyanions were the first reports in the RDL. The diffusion coefficients measured in the ODL were retarded compared to the values reported in water, and further retarded in the RDL for all elements with both methods. A DGT technique with mixed binding layer (MBL), containing both Chelex-100 and Metsorb, was validated for the measurement of Al at pH 4.01 and pH 8.30, where the dominant species shifts from cationic to anionic, respectively. The performance of this DGT- MBL was then evaluated in various coastal sites over a wide range of pH, for the simultaneous measurement of Al and other cationic and oxyanionic metals using both ODL and RDL. The results were compared to the 0.45 µm-filterable and also the measurements of individual binding layers to investigate the selectivity of each DGT type for trace metals. All measured concentrations with all measurement types were compared to the water quality guidelines defined by the Australian and New Zealand Environment and Conservation Council (ANZECC) to assess the environmental health of the studied field sites. The in-situ application of DGT-MBL confirmed the utility of this approach compared to the use of individual DGT-Chelex and DGT-Metsorb samplers, especially for metals like aluminium with complex speciation.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Andrade, Carlos Francisco Ferreira de. "Avaliação in situ da especiação de metais no estuário da Lagoa dos Patos utilizando o sistema DGT". reponame:Repositório Institucional da FURG, 2005. http://repositorio.furg.br/handle/1/3525.

Texto completo

Resumen

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Oceanografia Física, Química e Geológica, Instituto de Oceanografia, 2005.
Submitted by Cristiane Silva (cristiane_gomides@hotmail.com) on 2013-01-28T12:25:06Z No. of bitstreams: 1 2005_Carlos_de_Andrade.pdf: 1453728 bytes, checksum: 61ca4996bcaf13cd39bc0418f7b5608b (MD5)
Approved for entry into archive by Bruna Vieira(bruninha_vieira@ibest.com.br) on 2013-06-13T18:51:07Z (GMT) No. of bitstreams: 1 2005_Carlos_de_Andrade.pdf: 1453728 bytes, checksum: 61ca4996bcaf13cd39bc0418f7b5608b (MD5)
Made available in DSpace on 2013-06-13T18:51:07Z (GMT). No. of bitstreams: 1 2005_Carlos_de_Andrade.pdf: 1453728 bytes, checksum: 61ca4996bcaf13cd39bc0418f7b5608b (MD5) Previous issue date: 2005
A cidade de Rio Grande, localizada às margens do estuário da Lagoa dos Patos, possui uma intensa atividade portuária e industrial, fatores que promoveram nas últimas décadas, alterações significativas nas paisagens e na degradação dos recursos hídricos, incluindo a contaminação por nutrientes e por metais. Por ser um estuário semi-fechado, possui uma alta taxa hidrodinâmica, condicionada principalmente pela força e direção dos ventos. Os ciclos biogeoquímicos naturais dos metais na coluna dágua, podem ser alterados devido ao lançamento de metais oriundos das atividades humanas. Alterações na fração dos metais podem ocasionar uma maior biodisponibilidade destes elementos para os organismos. A determinação das espécies de metais biodisponíveis (lábil) por técnicas instrumentais ou analíticas, possuem implicações quanto à obtenção da concentração representativa do meio, por estar sujeita a erros de amostragem e preparo das amostras. Com o desenvolvimento da técnica de gradiente difusivo de membranas (DGT), obtem-se a concentração da fração lábil in situ em distintos ambientes sob diversas condições de pH, temperatura e salinidade. O presente trabalho tem como objetivo avaliar e aplicar a técnica DGT, para o monitoramento e detecção da concentração de elementos traço em distintos locais da área estuarina da Lagoa dos Patos. Para avaliar a aplicabilidade da técnica para o estuário, foram considerados dois períodos de exposição do sistema DGT em três locais: um com pouca influência (Ilha dos Marinheiros - IM) e dois com maior influencia dos despejos industriais e urbanos (Capitania dos Portos - CP e Museu Oceanográfico - MO). Para o primeiro período de exposição (2, 6 e 10 dias) das unidades de DGT foram analisados Cd, Co, Cu, Mn, Ni, Pb e Zn em DGT e água nos locais IM e CP. Para o segundo período de exposição (2, 4, 6 e 8 horas) DGT e água foram analisados para Cd, Cu, Pb e Zn no local MO em duas amostragens, uma com salinidade intermediária (MO1) e a outra com salinidade alta (MO2). Para ambos períodos de exposições, amostras de água analisadas para a fração lábil de metais com resina Chelex 100, demonstraram concentrações distintas em comparação ao DGT, evidenciando a diferença entre os dois métodos. Os resultados no DGT para o primeiro período de exposição (IM e CP) mostraram um decréscimo nas concentrações de todos os elementos, com o aumento do tempo de exposição. Isto provavelmente tenha ocorrido devido à baixa concentração de metais lábeis na água e/ou possível presença de biofilm nas unidades de DGT. Não foram reveladas concentrações significativas de Cu, Pb, Ni e Zn nos locais IM e CP. Para o segundo período de exposição, as concentrações de metais foram mais elevadas para Cd, Cu e Pb em alta salinidade (MO2), além de ter indicado aporte para este elementos no meio, quando comparado com outros estuários. Em conseqüência das variabilidades do estuário, conclui-se que uma resposta mais representativa para o sistema DGT, seria mantê-lo num período fixo de 8 a 48 horas em exposição no ambiente.
Rio Grande is a city located in the margin of the Patos Lagoon estuary and its maritime harbour and industries are very developed. During the last decades, these activities were responsible for many changes of the landscape and degradation of water resources, including contamination by nutrients and metals. This semi-closed estuary has a high hydrodynamic rate, which is determined manly by the wind direction and strength. The natural biochemical cycles of metals can be modified by discharge of metals originated by human activities. Changes in the metal fractions can lead to a higher bioavailability of these elements to the organisms. The determination of bioavailable (labile) metals by instrumental or analytical techniques can have implications on the representative environmental concentration, since errors during sample collection and preparation can occur. The development of the diffusive gradient thin-films (DGT) technique made possible the determination of labile metals in situ in distinct environments with different conditions of pH, temperature and salinity. The main objective of the present study is to apply and to evaluate the DGT technique, for the monitoring and detection of trace elements concentrations in different areas of the Patos Lagoon estuary. To evaluate the applicability of this technique to the estuary, two deployment periods of the DGT units were considered in three areas: one with low antropogenic influence (Ilha dos Marinheiros – IM) and two in high urban and industrial discharge areas (Capitania dos Portos – CP – and Museu Oceanográfico – MO). For the first period of the DGT deployment (2, 6 and 10 days) DGT and water samples were analyzed for Cd, Co, Cu, Mn, Ni, Pb and Zn at the IM and CP sites. For the second deployment period (2, 4, 6 and 8 hours), Cd, Cu, Pb e Zn were analyzed for DGT and water samples were collected at the MO point, during two different conditions of salinity, one with intermediate values (MO1) and the other with high salinity (MO2). For both deployment periods, water samples analyzed for labile fraction with Chelex-100 resin showed distinct concentrations, when compared with the DGT, indicating differences between the two methods. The DGT results showed for the first deployment period (IM and CP) a decrease with time in the concentration for all elements. Probably this had occurred due to variations on the labile form of the metals and/or the presence of biofilm. No significant differences were found in the concentration of Cu, Pb, Ni and Zn between IM and CP sites. For the second deployment period, trace metal concentrations showed higher values for Cd, Cu and Pb during high salinity (MO2) condition, as well as indicating input of these elements in the surroundings when compared with other estuaries. As a consequence of variability’s in the estuary, it can be concluded that for a more representative result of the DGT units, these should be deployed during 8 to 48h on a fixed period in the environment.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Fozard, Susan. "Development and applications of the DGT (diffusive gradients in thin-films) technique for the measurement of Mo and W in waters and soils". Thesis, Lancaster University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.654735.

Texto completo

Resumen

Molybdenum and tungsten are present in the environment as the oxyanions molybdate (MoOl-) and tungstate (WOll Measurements of available Mo and W in soils and waters have been stalled by the lack of a suitable technique. Diffusive gradients in thin films (DGT) is an in situ tool that allows the direct measurement of metal ions accumulated over a given time. This work provides the fIrst systematic investigation on the performance of DGT, containing a binding layer comprising of a single Feoxide reagent, for the measurement of Mo and W in soils and waters. The performance characteristics of DGT, were unaffected by solution conditions likely to be encountered in the environment (PH and ionic strength). DGT effIciently and effectively measured concentrations of labile Mo and W in streams and soils. In laboratory experiments complexation with humic substances was shown to occur with the strongest complexation being observed for HA. Toxicity assays showed that exposure to Mo and W resulted in weight loss, reduced reproduction and bioaccumualtion of Mo within the tissues of earthworms. Collectively these results showed that DGT, using Fe-oxide as the single binding layer, behaves predictably over a wide range of solution conditions and is a suitable and robust passive sampling technique for the measurement of Mo and W in natural environments.

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Chang, Ling-Yun. "Development and application of diffusive gradients in thin-films (DGT) for the measurement of stable and radioactive caesium and strontium in surface waters". Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264116.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Jabbar, Rawaa Abdullatif Abdul. "Using the DGT to investigate the soil chemistry of P and Cd in sandy loam soil after the application of phosphorus fertilizers". Thesis, Griffith University, 2019. http://hdl.handle.net/10072/386826.

Texto completo

Resumen

A recently developed DGT with a mixed binding layer of Chelex and Metsorb (TiO2) was successfully deployed in fresh and seawater to simultaneously measure available cations and anions. But, to date, no studies have used similar DGTs in soils. This study used the Metsorb Gel in two types of DGTs the Metsorb Chelex Mixed Binding layer (MBL-DGT) and the Metsorb Chelex Double Binding layer (DBL-DGT) or sandwich DGT to determine the concentration of available P and Cd (CDGT) in soil. Three experiments were conducted to assess the accuracy, sensitivity, and capacity of the new DGTs to measure the availability of P and Cd (CDGT) in a sandy loam soil. The study also investigated the relationship between the CDGT of P and Cd in the soil and concentrations of available P and Cd in plants and leachate water. Three scenarios were prepared for the assessment of the DGTs. First, the MBL-DGT was deployed in a large-scale flume filled with sandy loam soil, which was fertilized with Single Super Phosphate (SSP) of three different doses (0.01, 0.1, and 0.5 mg P L-1). Second, a biological experiment was conducted in a greenhouse using the tomato plant (Lycopersicon esculentus) as an indicator to assess the reliability of the CDGT of the available P and Cd measured in soil solution and that absorbed by the plants. This experiment used the same type of sandy loam soil, with three types of P fertilizers: SSP, Egyptian Reactive Phosphate (ER) and phosphorus soft rock from Nutri-tech Solution (NTS) applied at four dosages (0, 100, 200 and 250 kg P ha-1). Third, three consecutive doses of the three fertilizers were added to the sandy loam soil to investigate the capacity of the MBL-DGT. The repeated fertilizer application simulated the repeating application of P fertilizer in the field cycle. The mobility of available P and Cd to the leachate water was monitored by deploying the DGTs at different depths in the soil. This technique was used to evaluate the sensitivity of the DGTs when deployed in the soil for 4, 7 and 14 days. In addition, the new DGT measurements were compared with conventional measurements of P and Cd, using the Olsen and NH4Cl extraction techniques, respectively. Results of all three experiments confirmed that the MBL-DGT and the DBL-DGT were versatile measures of P and Cd availability and mobility in soil. The Metsorb mixed binding layer uptake of iii P and Cd rose with increasing P fertilizer dose. The new DGTs were sensitive to fertilizer type due to the differences in the solubility properties of the three fertilizers. The new DGTs showed that the excessive use of P fertilizers in the sandy loam soil increased the mobility of available P and Cd to the leachate water. PDGT and CdDGT had stronger correlations with P and Cd content in the plants than the conventional P and Cd extraction methods. These findings indicated that the DBL-DGT mimicked the process of plant P uptake. The MBL-DGT was also able to measure the most plant accessible form of Cd from the soil solution. MBL-DGT measurements of P and Cd were also better correlated with total P and Cd than those of conventional extraction methods. The capacity of the MBL-DGT for Cd uptake did not exceed the effective capacity of the MBL-DGT previously recorded by Panther et al. (2010). On the other hand, the MBL-DGT capacity for available P uptake was 42,000 ng per disc which was slightly higher than that recorded by Panther et al. (2014). Quantitative assessment of available P in the soil which has recently received high doses of P fertilizer will require MBL-DGTs with higher capacity. Further research is needed on different soil types and different crops to obtain a more comprehensive understanding of when the MBL-DGT can be practically applied in the field.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Soares, Jose Antonio. "An investigation of early diagenetic processes in marine coastal environments by the diffusive gradient in thin films (DGT) technique". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246223.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Reichstädter, Marek. "Využití techniky difúzího gradientu v tenkém filmu v analýze potravin a v environmentální analýze". Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2020. http://www.nusl.cz/ntk/nusl-433012.

Texto completo

Resumen

Tato dizertační práce zkoumá vývoj techniky difúzního gradientu v tenkém filmu (DGT) pro stanovení rtuti (Hg) a dalších stopových kovů a dále rozšířené možnosti použití této techniky. Technika DGT je v této práci vyvinuta pro stanovení Hg a dalších stopových prvků v různých kapalných médiích. Dvě rozdílná sorpční média specifická pro rtuť byla testována pro použití v technice DGT – Purolite S924 a cysteinem modifikovaná aminopropyl silika (CAPS). Purolite S924 je komerčně dostupný chelatační iontoměnič, CAPS byla připravena v laboratorních podmínkách imobilizací cysteinu na 3-aminopropyl funkcionalizovanou siliku pomocí glutaraladehydu. Obě testovaná sorpční média ukázala slibný aplikační potenciál pro užití v technice DGT díky funkčnosti v roztocích o širokém rozsahu pH i iontové síly. Funkčnost DGT s novými sorpčními médii byla porovnána s technikami DGT s běžně používanými sorbenty Chelex-100 a 3-merkaptopropylfunkcionalizovanou silikou. Hlavní výhodou sorpčních médií Purolite S924 a CAPS je schopnost současného stanovení Hg a dalších stopových kovů (Cd, Pb, Co, Ni, Cu). Vzhledem k odlišným požadavkům na sorpční média používaná v technice DGT nebylo dosud současné kvantitativní stanovení Hg a dalších stopových kovů možné. Doposud byly zapotřebí dvě samostatné techniky DGT – jedna pro Hg a druhá pro další stopové kovy, což zvyšuje množství vzorků pro analýzu a množství použitého spotřebního materiálu. Technika DGT s CAPS byla použita pro stanovení koncentrací kovů v námořních přístavech v Oostende a Zeebrugge na belgickém pobřeží Severního moře. Přestože byla technika DGT původně představena pro použití v analytické chemii životního prostředí, byla v této práci zkoumáno i použití této techniky v analýze potravin. V prostředí rybí omáčky byla ověřena funkčnost techniky DGT a stanoveny difúzní koeficienty Hg a dalších stopových prvků. Technika DGT byla následně použita pro stanovení koncentrace rtuti a dalších stopových kovů v různých komerčně dostupných vzorcích rybí omáčky. Výsledky nově navrhnutého analytického postupu s použitím techniky DGT byly porovnány s výsledky přímé analýzy atomovou absorpční spektroskopií s termální dekompozicí a amalgamací zlatem (TD-AAS) a po mikrovlnném rozkladu vzorků omáčky také s výsledky sektorové hmotnostní spektrometrie s indukčně vázanou plazmou (SF-ICP-MS). Díky předkoncentrační schopnosti techniky DGT byly dosaženy nižší detekční limity ve srovnání s TD-AAS nebo SF-ICP-MS. Technika DGT díky schopnosti oddělení analytů z komplexní matrice rybí omáčky rovněž snížila opotřebení a koroze kovových částí použitých instrumentálních technik.

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

Colon, i. Bosch Mireia. "Analytical strategies based on inductively coupled plasma sprectroscopy (ICP) and diffusive gradients in thin fims (DGT) techniques for the assessment of environmental pollution indicators". Doctoral thesis, Universitat de Girona, 2011. http://hdl.handle.net/10803/84050.

Texto completo

Resumen

In this thesis, simple methods to determine sulfide at low levels (µg L-1) in aqueous samples and sediments by water free hydrogen sulfide vapor generation using a commercially available vapor generation accessory have been developed. The hydrogen sulfide is then introduced in the ICP-QMS, equipped with an octopole collision/reaction cell which is vented with hydrogen and helium gases, or in the ICP-AES where the optical path between the plasma and the monochromator is purged with nitrogen. Moreover some studies have been conducted for the determination of arsenic by ICP-MS in natural waters with high sodium and chloride content. Spectral and non spectral interferences on arsenic measurement have been investigated and different experiments have been developed to solve such interferences (optimizations of the cell collision conditions, arithmetic corrections, introduction of small amounts of alcohol). Finally, the use of the DGT technique (diffusive gradients in thin films) has been evaluated in acidic samples and mining wastes for the firs time.
En aquesta tesi, s’han desenvolupat mètodes senzills per a la determinació de sulfur a baixes concentracions (µg L-1) en mostres aquoses i sediments mitjançant la generació de sulfur d’hidrogen, utilitzant un accessori de generació d’hidrurs comercial. Un cop format el sulfur d’hidrogen, aquest es pot introduir a l’ICP-QMS, equipat amb una cel•la de col•lisió/reacció o a l’ICP-AES amb el pas entre el plasma i el monocromador purgat amb nitrogen. També s’han fet alguns estudis per determinar arsènic amb ICP-MS en aigües naturals amb alt contingut de sodi i clor. S’han estudiat les interferències espectrals i no espectrals sobre aquest element i s’han dut a terme diferents experiments per a resoldre-les (optimització de la cel•la de col•lisió, aplicació de correccions matemàtiques, introducció de petites quantitats d’alcohol). Finalment, s’ha avaluat l’ús de la tècnica de DGT (diffusive gradients in thin films) en mostres àcides (pHs de 5 a 10) i residus de mineria per primera vegada.

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

Turull, López Marta. "Novel developments in the Diffusive Gradient in Thin films (DGT) technique for the determination of bioavailable mercury and other trace metals in aquatic and terrestrial environments". Doctoral thesis, Universitat de Girona, 2019. http://hdl.handle.net/10803/668780.

Texto completo

Resumen

This thesis is focused on the use of the Diffusive Gradient in thin film (DGT) technique for the analysis of bioavailable mercury and other trace metals in water and soil. Homemade DGT devices using a selective ion-exchange resin, and a polyacrylamide gel as the diffusive layer using an open resin (>5 nm), have been used to determine the labile Hg in different aquatic systems, concretely in the Ebro river (Spain) and Tully river (Australia). Besides, a new design of DGT using a bis-acrylamide as a restricted layer (<1 nm) has been performed to determine different species of Hg in agricultural soils. On the other hand, using Chelex-100 as the resin in the DGT devices allowed the analysis of bioavailable trace metals and further correlation with the plant uptake, specifically by lettuces (Lactuca sativa)
Aquesta tesi està basada en l’aplicació de la tècnica de Gradient de Difusió en capa fina (DGT) per a l’avaluació de la biodisponibilitat del mercuri i altres metalls en agua i sòl. Es van realitzar dispositius DGT al laboratori basats en una resina selectiva, juntament amb poliacrilamida com la capa de difusió, anomenat de “capa oberta” (>5 nm), utilitzats per a la determinació de mercuri biodisponible en diferents sistemes aquàtics, concretament en el riu Ebre (Espanya) i el riu Tully (Austràlia). A més, es va dur a terme un nou disseny de dispositiu DGT utilitzant bis-acrilamida, anomenat de “capa restringida” (<1 nm), per a la determinació d’espècies inorgàniques de mercuri en sistemes agrícoles. Per altra banda, s’ha utilitzat la resina Chelex-100 per a l’estudi de la biodisponibilitat d’altres metalls a més de correlacionar els resultats obtinguts amb l’absorció de metalls en planta, concretament en enciams (Lactuca sativa)

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

Szkandera, Roman. "Vývoj techniky difúzního gradientu v tenkém filmu (DGT) pro stanoveni rtuti ve vodných systémech". Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-233340.

Texto completo

Resumen

The theoretical part of this doctoral thesis deals with determination of mercury and its species in aquatic systems. Special attention is paid to the use in situ sampling technique diffusive gradients in thin films technique (DGT) and its development. Current resin gels used for determination of mercury by DGT technique Duolite GT-73, Chelex-100 and Spheron-Thiol are described. Moreover, new types of resin gels including Iontosorb AV modified by imidazole or 6-mercaptopurine and commercially available titanium dioxide. Preparations of resin gels and their basic tests in model solution according to DGT Research are described. Mercury accumulation in relation to time and basic recovery test were tested and capacity of resins was determined. All tested resins meet the requirements of basic DGT Research tests and relative standard deviations of mercury in recovery tests were lower than 10 %. The sorption capacity of resins varied from 1,5 to 6 µmol.l-1 and decreased in following order: Duolite GT-73 > ISAV-IM > Chelex-100 > Spheron-Thiol > TiO2 > ISAV-MP. Mercury sorption on resins was investigated under conditions similar to those in natural waters. It was found that the ionic strength commonly occurring in natural waters does not affect the determination of mercury. The presence of chlorides significantly affects the determination of mercury using DGT with titanium dioxide and therefore this sorbent can not be recommended for the determination of mercury in sea waters. The accumulated amount of mercury, depending on the pH shows that all the sorbents can be used in natural waters with pH in the range form 4 to 8. Mercury sorption is most affected by the presence of humic acids, especially at ion-exchange resins containing other than thiol functional groups. The exception is titanium dioxide for which physical sorption of humic acid metal complexes is typical. Cadmium and copper in model solutions in the molar balance of the excess mostly influenced the sorption of mercury on Chelex-100 and Spheron-Thiol resins. After laboratory tests, the DGT units with studied sorbents were used for the determination of mercury in natural waters of South Moravia (Svratka, Jihlava and Svitava river). Mercury concentration determined using DGT units containing Duolite GT-73 resin was comparable to the total dissolved concentration of mercury in river water provided by direct determination using AAS technique. Order of magnitude smaller concentrations than the total dissolved mercury concentration were found using DGT containing Spheron-Thiol and ISAV-MP resins. These sorbents are probably able to capture only mercury present in the form of labile complexes. This can be used for speciation analysis if more DGT units with different resins are deployed together. Subtracting the measured DGT Spheron-Thiol or ISAV-MP concentrations from the DGT Duolite GT-73 concentration, information about the amount of mercury present in the form of stabile complexes can be obtained. The amount of mercury determined after application of DGT units containing ISAV-IM, Chelex 100 or TiO2 can probably represent the mercury fraction bound in even weaker complexes than fraction determined by Spheron-Thiol and ISAV-MP DGT.

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Gontijo, Erik Sartori Jeunon [UNESP]. "Distribuição, complexação e mobilidade de íons arsênio em águas superficiais do Quadrilátero Ferrífero-MG/Brasil: ênfase nas interações com substâncias húmicas aquáticas". Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/150398.

Texto completo

Resumen

Submitted by ERIK SARTORI JEUNON GONTIJO null (sartori_jg@hotmail.com) on 2017-04-20T15:59:08Z No. of bitstreams: 1 Erik Sartori Jeunon Gontijo - Tese.pdf: 6303649 bytes, checksum: e2379a13e7e45d2ce94323eddce0a8bc (MD5)
Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-04-25T17:47:27Z (GMT) No. of bitstreams: 1 gontijo_esj_dr_soro.pdf: 6303649 bytes, checksum: e2379a13e7e45d2ce94323eddce0a8bc (MD5)
Made available in DSpace on 2017-04-25T17:47:27Z (GMT). No. of bitstreams: 1 gontijo_esj_dr_soro.pdf: 6303649 bytes, checksum: e2379a13e7e45d2ce94323eddce0a8bc (MD5) Previous issue date: 2017-03-27
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Deutscher Akademischer Austauschdienst (DAAD)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
O As está distribuído em diversas formas químicas em sistemas aquáticos, o que determina o seu comportamento e destino no ambiente. Nesse contexto, as substâncias húmicas (SH) têm um importante papel por serem capazes de complexar esse metaloide e alterar sua mobilidade e biodisponibilidade. O Fe também tem grande importância por poder formar complexos ternários SH-Fe-As. Apesar da química do As já ter sido bem estudada, o seu comportamento em ambientes ricos em SH e Fe ainda não é totalmente compreendido. Os objetivos desse trabalho foram investigar a distribuição do As, Al e Fe em águas superficiais de uma região mineira no sudeste do Brasil (Quadrilátero Ferrífero, QF) e entender como características de SH extraídas de diferentes regiões (Brasil e Alemanha) afetam a complexação do As(V) na presença de Fe(III). Amostras de águas foram coletadas em 12 pontos do QF, filtradas (0,45 µm) e ultrafiltradas (1 kDa) para separar as frações particulada (>0,45 µm), coloidal (<0,45 µm e >1 kDa) e livre (<1 kDa) de As, Al e Fe. A técnica de difusão em filmes finos por gradientes de concentração (DGT) foi usada em 5 dos 12 pontos para estudar a fração lábil dos elementos estudados. Carbono orgânico total (COT) e dissolvido (COD) também foram medidos. SH foram extraídas de quatro pontos (um no Brasil nas estações seca e chuvosa e três na Alemanha) para testar a influência de diferentes tipos de SH e Fe(III) na complexação do As(V). As SH foram caracterizadas e foram feitos testes de complexação utilizando sistema de ultrafiltração com membrana de 1 kDa. Todos os dados foram analisados pela rede neural de Kohonen. Os resultados mostraram que a maior parte do Al e Fe total no QF estava presente na fração particulada e o As na fração livre. A maior parte do Al e Fe dissolvido estava na fração coloidal e inerte, diferente do As que era mais lábil e potencialmente biodisponível. A maioria das amostras apresentou comportamento similar nas estações seca e chuvosa no QF. Diferenças entre os resultados de ultrafiltração e DGT foram atribuídos a distinções metodológicas e processos químicos. Os resultados de caracterização dos extratos mostraram que a maior parte do As e Fe estavam predominantemente nas frações de maior tamanho molecular. Todos os extratos de SH complexaram quantidades similares de As(V) nos testes de complexação, exceto o extrato do rio Selke, onde foi encontrado menos As(V) livre (mais complexado). Essa diferença foi atribuída ao S e à grupos N-C aromático na estrutura de SH. Isso reforça que a qualidade das SH é um importante fator capaz de influenciar o comportamento do As em ambientes ricos em matéria orgânica e Fe, que também pareceram ser fatores limitantes nas interações com o As. A rede neural de Kohonen foi uma ferramenta importante nas investigações de distribuição do As e complexação do As(V) por Fe(III) e SH.
As is distributed in different chemical forms in aquatic systems. These different forms control its behaviour and fate in the environment. The humic substances (HS) have an important role in the As cycle since they can complex this metalloid and change its mobility and bioavailability. Fe is also important because it can form ternary complexes HS-Fe-As. Although the As chemistry is well studied, the behaviour of As in HS and Fe-rich environments is not totally known. This thesis aimed to investigate the distribution of As, Al and Fe in surface waters from a mining region in the southeast of Brazil (Quadrilátero Ferrífero, QF) and understand how characteristics of HS extracted from different regions (Brazil and Germany) affect the complexation of As(V) in the presence of Fe(III). Water samples were taken in 12 points in QF, filtered (0.45 µm) and ultrafiltered (1 kDa) to separate the fractions particulate (>0.45 µm), colloidal (<0.45 µm and >1 kDa) and free (<1 kDa) of As, Al and Fe. The technique of diffusive gradients in thin films (DGT) was used in 5 of the 12 points to study the labile fraction of the elements studied. Total organic carbon (TOC) and dissolved organic carbon (DOC) were also measured. HS were extracted from four points (one in Brazil in dry and rainy seasons and three in Germany) to analyse the influence of HS from different origins and Fe(III) on the complexation of As(V). The HS were characterised and complexation experiments were performed using an ultrafiltration system with 1 kDa membrane. All data were analysed using the Kohonen neural network. The results showed that most of total Al and Fe in QF was in the particulate fraction and As was in the free fraction. Most of the dissolved Al and Fe was in the colloidal and inert fraction, while As was more labile and potentially more bioavailable. Most samples had similar behaviour in the dry and rainy seasons in the QF. Differences between results of ultrafiltration and DGT were attributed to methodological distinctions and chemical processes. The results of characterisation of extracts showed that most of As and Fe was in the fractions of higher molecular size. All HS extracts complexed similar amounts of As(V), except Selke, where a lower amount of free As(V) was detected (more complexed). This difference was attributed to S and N-aromatic C groups in HS structure. It supports that the quality of HS is an important factor able to influence the behaviour of As in environments rich in organic matter and Fe. The Kohonen neural network was an important tool in the investigation of the distribution of As and As(V) complexation by Fe(III) and HS.
FAPESP: 2012/17727-8

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

Sonmez, Osman. "A field-based assessment tool for phosphorus losses in the runoff in Kansas ; Effects of phosphorus and manganese oxides on soil lead bioavailibility ; Assessment of bioavailability of zinc by diffusive gradients in thin films (DGT) /". Search for this dissertation online, 2004. http://wwwlib.umi.com/cr/ksu/main.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Szkandera, Roman. "Testování modifikovaných sorbetů Iontosorb pro užití v technice difúzního gradientu v tenkém filmu (DGT)". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2008. http://www.nusl.cz/ntk/nusl-216360.

Texto completo

Resumen

6-mercaptopurine was joined by diazotation and copulation reactions on Iontosorb AV. Presence of thiol groups in modified resin was showed by infrared spectrometry. Amount of thiol groups was determined by iodometric titration. Resin gel was preparated from modified resin and agarose and both of them were tested for mercury determination by DGT technique.

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Finsterlová, Hana. "Studium vlastností sorpčních gelů pro stanovení rtuti technikou DGT". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2009. http://www.nusl.cz/ntk/nusl-216541.

Texto completo

Resumen

The aim of this thesis is testing of resin gels used in diffusive gradients in thin films technique (DGT) for determination of mercury in natural waters. The sorbets, chosen for preparation of resing gels were: Duolit GT- 73, Spheron- Thiol, and Chelex 100 and newly modified sorbent Iontosorb AV. At the beginning of work, the preparation procedure of all resing gels was optimized. After optimalization of preparation procedure the resin gels were tested in mercury model solutions. The recovery test and time dependence test were performed. When the basic tests were finished, they were followed by the tests of influence of natural ligand (humic acids and chlorides), and other parameters (above all pH and ionic strenght), on mercury determination by DGT technique.

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Mongin, Sandrine. "Contributions to the study of the availability of metal ions in aquatic systems". Doctoral thesis, Universitat de Lleida, 2012. http://hdl.handle.net/10803/90839.

Texto completo

Resumen

La disponibilitat de metalls per part dels organismes no depèn únicament de la concentració total sinó també de l'especiació d'aquestes subtancias. En general, la disponibilitat de les espècies metàl•liques en medis naturals per a organismes està determinada per un conjunt d'esdeveniments encadenats on el equilibri representa només un cas particular de la situació dinàmica general. Espècies poc definides químicament, com ara àcids húmics i fúlvics, actuen com a lligands de metalls i juguen un paper clau en la circulació i la determinació de les propietats ecotoxicològiques de les espècies metàl•liques en medis naturals. La polifuncionalitat dels àcids húmics i fúlvics és descrita en aquest estudi utilitzant mètodes termodinàmics i mecano-estadístics. La tècnica Diffusive Gradients in Thin films (DGT) s'ha utilitzat per mesurar el flux disponible de metall en un sistema sintètic que conté complexos metàl•lics. La principal conclusió d'aquest estudi és que el disc de resina quelant dels sensors juga un paper clau en la determinació del grau de labilitat d'un complex mesurat amb aquesta tècnica. D'altra banda, a un pH baix, o concentració alta de lligand, es pot aconseguir l'equilibri entre la resina del sensor i el metall en el si de la dissolució, pertorbant l'acumulació lineal a temps de contacte relativament curts. Es presenta una anàlisi d'aquests fenòmens, així com la seva justificació mitjançant models teòrics.
La disponibilidad de metales por parte de los organismos no depende únicamente de la concentración total sino también de la especiación de estas subtancias. En general, la disponibilidad de las especies metálicas en medios naturales hacia organismos está determinada por un conjunto de eventos encadenados cuyo equilibrio representa sólo un caso particular de la situación dinámica general. Especies poco definidas químicamente, tales como ácidos húmicos y fúlvicos, actúan como ligandos de metales y juegan un papel clave en la circulación y la determinación de las propiedades ecotoxicológicas de las especies metálicas en los medios naturales. La polifuncionalidad de los ácidos húmicos y fúlvicos es descrita en este estudio usando métodos termodinámicos y mecano-estadísticos. La técnica Diffusive Gradients in Thin films (DGT) se ha utilizado para medir el flujo disponible de metal en un sistema sintético que contiene complejos metálicos. La principal conclusión de este estudio es que el disco de resina quelatante de los sensores juega un papel clave en la determinación del grado de labilidad de un complejo medido esta técnica. Por otra parte, a un pH bajo, o a concentración alta de ligando, puede ser alcanzado el equilibrio entre la resina del sensor y el metal en el seno de la disolución, perturbando la acumulación lineal a tiempos de contacto relativamente cortos. Se presenta un análisis de estos fenómenos, así como su justificación mediante modelos teóricos.
Availability of metals for organisms does not depend only on the total metal concentration but also on speciation of these species. In general, the availability towards organisms is determined by a set of chained events whose equilibrium approach only represents a simplified limiting case of the general dynamic situation. Poorly defined species such as humic and fulvic acids, act as metal ligands and play a key role in the circulation and determination of the ecotoxicological properties of metal species in the natural media. Thermodynamic and statistical mechanics methods are here applied to describe the polyfunctionality of humic and fulvic acids. The Diffusive Gradients in Thin Films (DGT) has been used to measure the available metal flux in a synthetic system that contains metal complexes. A main conclusion of this study is that the chelating resin disc of the sensor plays a key role in determining the lability degree of a complex measured with DGT. Moreover, at relatively low pH, or in presence of high affinity ligands, the equilibrium with the bulk metal concentration can be approached in the sensor, disturbing linear accumulations at relatively short deployment times. Analysis of these phenomena and theoretical explanations are reported.

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Trávníčková, Jana. "Nové sorpční gely pro užití v technice difúzních gradientů v tenkých filmech". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2008. http://www.nusl.cz/ntk/nusl-216441.

Texto completo

Resumen

Diffusive gradients in thin films technique (DGT) is a simple preconcetration method for in situ determination of labile metal ions in aquatic systems. It eliminates contamination problems associated with the sampling and transport into the laboratory. The DGT technique is based on a simple device that accumulates metal ions on a cation-exchange resin, immobilized in thin layer of hydrogel, after passage through the diffusion layer. The cation-exchanger, usually Chelex 100, is selective for binding free or weakly complexed metal ions in solution. This diploma thesis deals with the characterization of a new resin gel based on ion exchanger with anchored thiol-functional groups, Spheron-Thiol, for DGT technique. This new binding agent with a high selectivity for „heavy“ metal ions could provide more information on the labile metal species in water systems. The performance of DGT technique with utilization of Spheron-Thiol resin was investigated by the determination of Cd, Cu, Ni and Pb under laboratory conditions. Due to the strong adsorption of copper to the Spheron-Thiol, it is necessary to decompose the resin gel in nitric acid prior to the determination. New resin gel provides reliable information of trace metal concentrations within the pH range 6 – 8 typical for natural waters. The effect of competitive ligands, iminodiacetic and humic acids, on Cd, Cu, Ni a Pb sorption on Spheron-Thiol and Chelex 100 resin gels was determined.

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Boman, Daniel. "Compositional gradients in sputtered thin CIGS photovoltaic films". Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355462.

Texto completo

Resumen

Cu(In,Ga)Se2 (CIGS) is a semiconductor material and the basis of the promising thin-film photovoltaic technology with the same name. The CIGS film has a typical thickness of 1-2 mm, and solar cells based on CIGS technology has recently reached efficiencies of 23.3%. Ultra-thin CIGS solar cells use sub-micrometer thick films that require significantly less material and can be manufactured in a shorter amount oftime than films with typical thicknesses. With decreasing thickness, both electrical and optical losses get more significant and lower the overall performance. Electrical losses can be decreased by increasing the overall film quality and by utilising a graded bandgap throughout the CIGS layer. The band gap can be changed by varying the[Ga]/([Ga]+[In]) (GGI) ratio. Higher overall film quality and a higher band-gap towards the back of the absorber are expected to increase the performance. In this work, sputtered CIGS solar cells were made with different CIGS layer thicknesses, that ranged between 550-950 nm. Increased heat during deposition was examined and shown to increase the film quality and performance for all thicknesses. Two different ways of doping CIGS with Na was examined and it was found that higher Na content lead to an increasing predominance of the (112) plane. The bandgap was graded by varying the GGI composition throughout the CIGS layer and depth profiles were made with Glow-Discharge Optical Emission Spectroscopy (GDOES). It was found that a sputtered CuGaSe2 (CGS)layer below the CIGS-layer lead to a steep increase of the GGI near the back contact. When CGS made up 10% of the total CIGS layer thickness, a significant increase in performance was observed for all thicknesses. CIGS-absorbers with a less graded region with low GGI, making up 30% or 60% of the total CIGS layer thickness were made. A decrease in GGI in that region, was shown to increase the current but lower the voltage. No substantial increase in total performance compared to a fully graded CIGS layer was seen regardless of layer thickness. For further work the optical losses needs to be addressed and work on increasing the optical path in the CIGS layer needs to be done.

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

Almeida, Eduardo de. "Determinação de metais na bacia do rio Piracicaba usando as técnicas de Difusão em Filmes Finos por Gradiente de Concentração (DGT) e Fluorescência de Raios X Dispersiva em Energia (EDXRF) e por Reflexão Total (TXRF)". Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/64/64135/tde-27022012-112202/.

Texto completo

Resumen

O desenvolvimento e aplicação de métodos analíticos na avaliação das concentrações de metais nas frações dissolvida e lábil na bacia do rio Piracicaba são de relevante importância para o estudo do comportamento químico-ambiental desses metais e para seu monitoramento, devido ao impacto das atividades antropogênicas nessa bacia. A técnica de difusão em filmes finos por gradiente de concentração (DGT, do inglês diffusive gradients in thin-films), é uma promissora ferramenta analítica de amostragem, pois permite pré-concentração, análise temporal, remoção de interferentes, avaliação lábil e amostragem in situ. A quantificação dos metais pelas técnicas de fluorescência de raios X dispersiva em energia por reflexão total (TXRF, total reflection X-ray fluorescence analysis) para amostras líquidas e da fluorescência de raios X dispersiva em energia (EDXRF, energy dispersive X-ray fluorescence) para amostras sólidas, mostram-se interessantes devido ao caráter multielementar, simultâneo e não destrutivo da análise. Neste trabalho avaliou-se a DGT para a determinação de Cr, Mn, Co, Ni, Cu, Zn e Pb em águas naturais, utilizando-se como agente ligante a membrana de celulose P 81 e como meio difusivo, o papel cromatográfico 3 MM. Calcularam-se os fatores de eluição e coeficientes de difusão para estes metais. Estudou-se o efeito da substância húmica, em diferentes concentrações, no desempenho da DGT para esses metais, e os resultados foram comparados e concordantes com as frações livre e a ligada à matéria orgânica, calculadas pelo programa Visual MINTEQ. Compararam-se o agente ligante e o meio difusivo à base de celulose, utilizados neste trabalho, com os à base de gel de poliacrilamida, empregando-se o complexante Chelex-100. Avaliou-se a homogeneidade da retenção dos analitos e do grupo ligante fosfato sobre a superfície do agente ligante. Nesses ensaios utilizaram-se soluções sintéticas contendo os analitos em pH 5,5 e força iônica 0,05 mol L-1 (ajustados com NaNO3). As determinações foram realizadas por TXRF e EDXRF. Avaliaram-se os acoplamentos DGT-SRTXRF e da DGT-EDXRF para a determinação da fração lábil de Cr, Mn, Co, Ni, Cu, Zn e Pb em amostras de água da bacia do rio Piracicaba, através de imersão em laboratório e in situ. Esses resultados foram comparados com as concentrações dissolvidas desses metais determinados pela técnica de fluorescência de raios X por reflexão total com excitação por luz síncrotron (SRTXRF, synchrotron radiation total reflection X-ray analysis). Os valores de concentrações de Mn, Cu e Zn nas frações dissolvida e lábil foram comparados com os valores máximos estabelecidos pela legislação brasileira Nas amostragens in situ, nos cinco pontos de coleta, as concentrações de Mn dissolvido e lábil foram maiores que a concentração total máxima permitida para esse elemento. Os elmentos Cr, Co, Ni e Pb, nas amostras coletadas, apresentaram-se abaixo do limite de detecção das técnicas SRTXRF (dissolvido), DGT-SRTXRF (lábil) e DGT-EDXRF (lábil). Os limites de detecção para o Cr, Mn, Co, Ni, Cu, Zn e Pb foram de 2,2 a 10 \'mü\'g L-1 na SRTXRF, de 0,21 a 3,6 \'mü\'g L-1 e de 7,2 a 24 \'mü\'g L-1 na DGT-SRTXRF e DGT-EDXRF, respectivamente
Analytical methods evaluation for metal dissolved and labile fractions determination in Piracicaba river basin is notable for metal-behavior studies in this environment as well as their monitoring due to anthropogenic activities. The diffusive gradients in thin films (DGT) is a promising sampling technique because of its pre-concentration, time-integrated, matrix interference removal, labile evaluation and in situ analytical features. The analytical techniques total reflection X-ray fluorescence (TXRF) for liquid samples and energy dispersive X-ray fluorescence (EDXRF) for solid samples analysis are advantageous due to simultaneous, multielemental and non-destructive characteristics. In this work, it was evaluated the DGT technique for Cr, Mn, Co, Ni, Cu, Zn and Pb determination in freshwater, using P 81 cellulose membrane as bind agent and 3 MM chromatographic paper as diffusive layer. Elution factors and diffusion coefficients were calculated for these metals. The humic acids effect on DGT performance was assessed and compared to free and humic acid bound metal fractions estimated by Visual MINTEQ software, in which agreement results were found. The paper-based DGT and gel-based one with Chelex-100 as bind agent were compared. The metal retention and phosphate group homogenization on P 81 membrane bind agent surface was studied. For these tests it was utilized a synthetic solution these metals containing with pH and ionic strength adjust to 5.5 and 0.05 mol L-1 (NaNO3), respectively. It was used the TXRF and EDXRF techniques for these metal quantifications. The DGT-SRTXRF and DGT-EDXRF were assessed in order to determine Cr, Mn, Co, Ni, Cu, Zn and Pb labile fractions in batch and in situ in Piracicaba river basin freshwater samples. These results were compared to their dissolved fractions by synchrotron radiation total reflection X-ray analysis, SRTXRF. The dissolved and labile Mn, Cu and Zn concentrations levels were compared to maximum allowed set by Brazilian legislation. The dissolved and labile Mn concentrations were higher than the maximum allowed in all five samples in situ sampling. Cr, Co, Ni, and Pb concentrations were lower than their limits of detection for dissolved fractions (SRTXRF) and labile ones (DGT-SRTXRF and DGT-EDXRF). The detection limits for Cr, Mn, Co, Ni, Cu, Zn and Pb were from 2.2 to 10 \'mü\'g L-1 for SRTXRF, from 0.21 to 3.6 \'mü\'g L-1 and from 7.2 to 24 \'mü\'g L-1 for DGT-SRTXRF and DGT-EDXRF, respectively

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

Mojsilovic, Ognjen. "Estimating bioaccessibility, phytoavailability and phytotoxicity of contaminant arsenic in soils at former sheep dip sites". Lincoln University, 2009. http://hdl.handle.net/10182/1142.

Texto completo

Resumen

Recognition that the bioavailability of soil As (As) is influenced by its soil dynamics has initiated research into development of more accurate, site-specific soil guideline values, departing from the assumption that the total soil As content is bioavailable. With the aim of deriving predictive models, the relationship between soil properties and As bioavailability (bioaccessibility and phytotoxicity) was examined on a set of naturally contaminated sheep dip soils (n = 30). Sampled soils were extensively characterised, bioaccessibility was estimated through an in vitro procedure, and soil As toxicity and availability to plants were evaluated using an early growth wheat bioassay. The in vitro bioaccessibility was consistently less than the total soil As content. Arsenic bioaccessibility was negatively correlated to soil iron (Fe), manganese (Mn) and aluminium (Al) contents, and it was positively related to the soil As loading. The in vitro extractable soil As concentrations were successfully modelled using linear combinations of soil As content, soil Fe and Mn determinations and soil pH. Differences in As phytotoxicity, expressed in terms of effective toxic concentration (EC50), between soils were directly related to soil Fe, Mn and Al contents. Available soil phosphorous (P) exerted an ameliorating effect on As toxicity, with the available soil As/P ratio representing the single best predictor of plant growth suppression. Plant P nutrition appeared to influence the relative selectivity for As and P by wheat, with greater selectivity for P demonstrated under P deficient conditions. Plant As uptake, its distribution, and also the plant nutrient status were all adversely affected by increasing soil As exposure. Co-contamination by Zn corresponded to a substantial elevation in proportion of the plant As allocated in shoots. Plant As levels exhibited a saturation-dependent relationship with increasing soil As. The best linear predictors of plant As levels in the non-toxic range were RHIZO-extractable and effective soil As concentrations, the latter based on the diffusive gradients in thin films (DGT) technique. Despite the complexity of soil As dynamics, large proportions in the variances exhibited by the two measures of bioavailability were explained using a small set of readily-available soil properties.

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Giri, Dipak. "Single-molecule spectroscopic studies of thin-film chemical gradients". Diss., Kansas State University, 2016. http://hdl.handle.net/2097/35225.

Texto completo

Resumen

Doctor of Philosophy
Department of Chemistry
Daniel A. Higgins
This dissertation describes the application of single molecule spectroscopy and tracking to investigations of the nanoscale properties of thin-film chemical gradients and the transport dynamics of molecules dispersed within and upon these gradients. Chemical gradients are surface bound materials that incorporate gradually changing chemical and/or physical properties. A continuous and gradual change in the properties of gradients are expected and often required for their intended applications, which range from directed growth of cell colonies to combinatorial materials science. In reality, such conditions are almost never met due to spontaneous demixing and dewetting processes that can lead to properties variations on microscopic length scales. A better understanding on the properties of chemical gradients on microscopic length scales will aid in the production of better engineered materials. Single molecule spectroscopy (SMS) allows for gradient properties to be probed on nanometer-to-micrometer length scales. In this dissertation, quantitative measurements of gradient polarity (i.e., dielectric properties) are made along a sol-gel derived thin film that incorporates a macroscopic polarity gradient. These measurements report on the microscopic heterogeneity of the gradient film, and point to the occurrence of phase separation of the polar and nonpolar components along the gradient. Single molecule tracking (SMT) provides an important means to examine the dynamics of molecular mass transport in thin films and on surfaces. In this dissertation, SMT is employed to study mass transport in thin water films condensed over monolayer wettability gradients under ambient environments. The results show that the rate and the mechanism of molecular transport depend on the surface wettability, and on the ambient relative humidity. Finally, wettability gradients have been broadly used to drive the transport of liquid droplets. In this dissertation, these applications are extended to achieve spontaneous stretching of DNA by the propulsion of liquid droplets along the gradient. Single molecule fluorescence imaging of DNA stretched along these gradients demonstrates that hydrophobic surfaces play an important role in DNA stretching. The study also shows the surface tension force acting at the gradient-droplet contact line (interface) to be responsible for DNA elongation and alignment. Overall, single molecule methods have been shown to be highly useful for better understanding the properties of chemical gradients as described in this dissertation.

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Sánchez, Rodríguez Daniel. "Obtaining advanced oxide thin films at low temperatures by chemical methods. Thermal analysis of thin films". Doctoral thesis, Universitat de Girona, 2015. http://hdl.handle.net/10803/328723.

Texto completo

Resumen

L'objectiu d'aquest treball és analitzar mètodes químics de baix cost com a ruta per a sintetitzar òxids avançats a baixa temperatura. En particular, hem explorat l'SHS per a la síntesi d'un òxid catalitzador fent servir pólvores de ciano complexes heteronuclears. També hem explorat el transport de calor per a sintetitzar capes via VCS concloent que les capes primes rarament experimentaran una combustió. Per això hem analitzat la condició necessària per que tingui lloc una combustió volumètrica en una mostra sòlida que reacciona sense intercanvi de gasos amb el seu entorn. Per fer-ho, hem ampliat el criteri de Frank-Kaminetskii per a sistemes d'escalfament continu i per a reactors cilíndrics. Per la part experimental em fet servir tècniques l'anàlisi tèrmica (TA). Hem desenvolupat un mètode per a mesurar la conductivitat tèrmica en pólvores per DSC. Finalment, hem desenvolupat dos criteris per a comprovar la fiabilitat en la mesura de la temperatura als experiments de TA.
The aim of this work is to analyse chemical methods as a route to synthesise advanced oxides at low cost and low temperatures. In particular, we have explored the combustion synthesis of a catalytic perovskite-type oxide from heteronuclear cyano complex powders. We have also explored heat transfer to synthesise films via VCS and concluded that thin films will hardly experience combustion. In particular, we have analysed the conditions needed for a thermal explosion to occur in a solid sample reacting without any gas exchange with its surroundings. For that purpose, we have extended the Frank-Kamenetskii relationship to continuous heating systems and to cylindrical reactors. The experimental component of this work is based on thermal analysis methods (TA). We have developed a new method to measure thermal conductivity of powders by DSC. Finally, we have developed two analytical relationships to check the reliability of the sample temperature in TA experiments.

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

Němec, Tomáš. "Formy vybraných kovů ve vodních systémech". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2008. http://www.nusl.cz/ntk/nusl-216358.

Texto completo

Resumen

The diffusive gradient in thin films technique (DGT) was used to measure concentration of labile metal-species (Cu, Ni, Pb) in the waste water from Faculty of Chemistry, Brno University of Technology.

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Paříková, Lucie. "Rtuť v odpadních vodách". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2008. http://www.nusl.cz/ntk/nusl-216362.

Texto completo

Resumen

In the time period from November to April of the academic year 2007/2008 presence of mercury and its forms was monitored in the waste waters of Faculty of Chemistry, VUT in Brno. The level of mercury was determined as total mercury with help of the atomic absorption spectrometry method and in available forms by diffusive gradient in thin film technique.

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Hwang, Pey-Hua B. (Pey-Hua Betty) 1982. "The use of soft lithography to reproduce snail-like movement by creating pressure gradients in thin films". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32806.

Texto completo

Resumen

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 18-20).
By imitating nature, man finds ways to expand his capacities. To achieve this aim, he often takes natures designs, simplifies them to their most basic principles and then works in a retrograde fashion to add back the complexity originally stripped away to make the first discoveries. This thesis is based on previous work done on modeling snail movement on a macroscopic scale using a motor driven wave propagation machine. This project scaled down the mechanism to a size more commonly found in nature. This downscaling required a new method for producing waves. Peristaltic pumping achieved through the use of soft-lithography and pneumatics was the method chosen. This combination of ideas proved challenging for several reasons. First, the pumping method had previously only been used with one channel per pneumatic input, whereas the snail required each input to feed a multitude of branching channels creating a more complicated fluid dynamics problem. Second, the snail waves were downscaled from a continuous sinusoid to the three phase stepping mechanism of the peristaltic pump. Each three-phase cycle was considered equivalent to one wavelength. Thus, after creating a design that could move, the ratio between the traveling wavelength speed and subsequent net movement were compared to the aforementioned mathematical model. The model's ratio was 0.56 net/wave velocity. The actual ratio was .05 net/wave velocity. The difference by an order of magnitude could be attributed to the discontinuity of the pumping mechanism as opposed to the continuous nature of an actual traveling wave.
by Pey-Hua B. Hwang.
S.B.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

Piovano, Paulo. "Evolution and Regularity Results for Epitaxially Strained Thin Films and Material Voids". Research Showcase @ CMU, 2012. http://repository.cmu.edu/dissertations/96.

Texto completo

Resumen

In this dissertation we study free boundary problems that model the evolution of interfaces in the presence of elasticity, such as thin film profiles and material void boundaries. These problems are characterized by the competition between the elastic bulk energy and the anisotropic surface energy. First, we consider the evolution equation with curvature regularization that models the motion of a two-dimensional thin film by evaporation-condensation on a rigid substrate. The film is strained due to the mismatch between the crystalline lattices of the two materials and anisotropy is taken into account. We present the results contained in [62] where the author establishes short time existence, uniqueness and regularity of the solution using De Giorgi’s minimizing movements to exploit the L2 -gradient flow structure of the equation. This seems to be the first analytical result for the evaporation-condensation case in the presence of elasticity. Second, we consider the relaxed energy introduced in [20] that depends on admissible pairs (E, u) of sets E and functions u defined only outside of E. For dimension three this energy appears in the study of the material voids in solids, where the pairs (E, u) are interpreted as the admissible configurations that consist of void regions E in the space and of displacements u of the atoms of the crystal. We provide the precise mathematical framework that guarantees the existence of minimal energy pairs (E, u). Then, we establish that for every minimal configuration (E, u), the function u is C 1,γ loc -regular outside an essentially closed subset of E. No hypothesis of starshapedness is assumed on the voids and all the results that are contained in [18] hold true for every dimension d ≥ 2.

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Hutter, Naima A., Marin Steenackers, Andreas Reitinger, Oliver A. Williams, Jose A. Garrido y Rainer Jordan. "Nanostructured polymer brushes and protein density gradients on diamond by carbon templating". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138812.

Texto completo

Resumen

Micro- and nanostructured polymer brushes on diamond can be directly prepared by carbon templating and amplification of the latent structures by photografting of a broad variety of vinyl monomers such as styrenes, acrylates and methacrylates. Even template structures with lateral dimensions as small as 5 nm can be selectively amplified and defined polymer brush gradients of a variety of functional polymers are realizable by this technique. Furthermore, conjugation with a model protein (GFP) results in protein density gradients of high loading and improved chemical stability. The effective functionalization of chemically and biologically inert diamond surfaces with stable functional polymer brushes, the possibility of structuring by the carbon templating technique and the direct biofunctionalization are crucial steps for the development of diamond based biosensors
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

Hutter, Naima A., Marin Steenackers, Andreas Reitinger, Oliver A. Williams, Jose A. Garrido y Rainer Jordan. "Nanostructured polymer brushes and protein density gradients on diamond by carbon templating". Royal Society of Chemistry, 2011. https://tud.qucosa.de/id/qucosa%3A27783.

Texto completo

Resumen

Micro- and nanostructured polymer brushes on diamond can be directly prepared by carbon templating and amplification of the latent structures by photografting of a broad variety of vinyl monomers such as styrenes, acrylates and methacrylates. Even template structures with lateral dimensions as small as 5 nm can be selectively amplified and defined polymer brush gradients of a variety of functional polymers are realizable by this technique. Furthermore, conjugation with a model protein (GFP) results in protein density gradients of high loading and improved chemical stability. The effective functionalization of chemically and biologically inert diamond surfaces with stable functional polymer brushes, the possibility of structuring by the carbon templating technique and the direct biofunctionalization are crucial steps for the development of diamond based biosensors.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Acremont, Quentin d'. "Étude des propriétés thermiques de librairies d’alliages ternaires en couches minces et mise en évidence du transport non-diffusif par spectroscopie thermique pompe-sonde femtoseconde". Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0665/document.

Texto completo

Resumen

Durant ces travaux, nous nous sommes intéressés à l’étude des transferts thermiques aux nano-échelles dans les couches minces par spectroscopie pompe-sonde femtoseconde. Dans un premier temps, nous nous sommes intéressés à la mesure haute-cadence de la conductivité thermique d’alliages de Fe-Si-Ge et Ti-Ni-Sn, dans le but d’optimiser leur processus de fabrication et de créer une base de données des propriétés thermiques de ces matériaux. Afin de pouvoir mesurer une grande quantité d’échantillons en un temps réduit, un système de mesure haute cadence entièrement automatisé a été développé et utilisé avec succès. Dans un second temps,ces travaux ont portés sur l’étude du transport thermique dans trois matériaux (Ge, GaAs In-GaAs) par spectroscopie pompe-sonde femtoseconde. Une nouvelle méthode de mesure de la réponse spectrale des nanomatériaux sur une gamme de fréquences allant de quelques centaines de kHz jusqu’au THz a été développée. Les mesures à l’aide de cette méthode ont permis de confirmer la présence d’un régime de transport qualifié de quasi-balistique dans certains matériaux,et une méthode d’extraction de propriétés thermiques à partir de la réponse spectrale mesurée, et prenant en compte ces effets quasi-balistiques, a été développée. L’ensemble des résultats obtenus par ces nouvelles méthodes confirment les travaux précédents décrits dans la littérature. Enfin, la mesure de la réponse spectrale d’un nano-matériau à haute fréquence est en grande partie limitée par la gigue des cavités lasers utilisées par l’expérience. Ainsi, la dernière étape a été de développer un système de mesure de cette gigue et de synchronisation de cavités laser qui pourra permettre de repousser la limite des fréquences mesurables par spectroscopie pompe-sonde femtoseconde
In this work, we studied ultrafast thermal transport at nanoscale in thin films by femtosecond pump-probe thermal spectroscopy. We first developed a high-throughput heterodyne thermoreflectance setup that allows the extraction of thermal properties of a large number of sample in a minimum time, aiming at creating a database of these properties for a large numberof thin film ternary alloys with thermoelectric potential. In the second part of this work, wefocused on the study of thermal transport in three materials : Ge, GaAs and InGaAs. A high resolution phonon spectroscopy setup, along with a spectral reconstruction method allowed usto measure the response of these materials up to several tens of GHz in Fourier domain, which highlighted the presence of non-diffusive thermal transport in InGaAs. Non-diffusive theory,based on Lévy dynamics, allowed us to model this superdiffusion phenomenon and to extract coherent, frequency-independant thermal properties of these materials. Also, high frequency(>GHz) measurements of these spectral responses have shown interesting effects related to the ultrafast thermalisation in transducer-like very thin films. Finally, high-frequency thermal spectroscopy is inherently limited by the intrinsic timing jitter of laser cavities. Thus, the last partof this work was dedicated to developing a timing jitter measurement and active laser synchronisation system in order to increase the signal-to-noise ratio and access higher frequencies in pump-probe thermal spectroscopy experiments

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Mason, Sean David. "Diffusive gradients in thin films (DGT) as a technique to predict nutrient availability to plants". 2007. http://hdl.handle.net/2440/57973.

Texto completo

Resumen

The soils of Australia have extensive macro and micronutrient disorders varying greatly in their capacities to provide the chemical nutrients essential for plant growth. Assessment of nutrient availability in soils is important in order to maximise fertilizer efficiency and crop yields and to minimise environmental pollution associated with over fertilisation. Nutrient availability has proven difficult to assess due to the complexity of trace element soil chemistry and plant uptake mechanisms. The relatively new method, Diffusive Gradients in Thin Films ( DGT ), provides the potential to become an alternative soil test that could accurately predict nutrient availability. To date, DGT technology has only been designed for separate assessment of anionic and cationic species in waters or soils typically at concentrations characteristic of highly contaminated systems. In this study a new mixed binding gel ( MBL ) was developed capable of simultaneous assessment of cations and anions in a single assay at concentrations more representative of uncontaminated agricultural soils, sediments and waters. The MBL has the potential to eliminate measurement errors associated with very fine spatial scale changes in element concentrations in these environments. The MBL consisted of ferrihydrite and Chelex - 100 cation exchange resin combined together in a binding gel. Results from the MBL were comparable to experiments performed using individual Chelex gels and ferrihydrite gels that have been shown to work successfully for DGT methodology. To facilitate combined analysis of P and cations by ICP - MS, HCl ( 1 M ) was used for gel elution to minimise interferences from [superscript 14] N [superscript 16] OH or [superscript 15] N [superscript 16] O on [superscript 31] P. All elements tested ( Cd, Cu, Mn, Mo, P and Zn ) were bound successfully to the MBL. DGT measurements obtained using the MBL on agricultural soils correlated well ( r ? = 0.95 ) with measurements obtained using pure Chelex and ferrihydrite binding layers. This suggests that the MBL could be used for simultaneous measurement of cationic and anionic element availability in soils. Performance of the Diffusive Gradient in Thin Films ( DGT ) technique was compared with three other common testing methods ( Colwell, Olsen, Resin ) for available soil P in terms of the ability of each to predict wheat, canola, lupin and barley responsiveness to applied P on 21 Australian agricultural soils. DGT accurately predicted plant responsiveness in > 90 % of the soils used. In contrast the other soil testing methods failed to correctly predict plant response to P on numerous occasions. These observations reveal that the DGT technique with the newly developed MBL can predict plant available P on these soils with greater accuracy than other traditional soil P testing methods and could become a useful tool for predicting P fertilizer requirements. The DGT method using the MBL was also used to test Zn deficiency thresholds for canola and wheat in a manufactured soil ( acid washed sand ). DGT successfully determined the threshold for Zn deficiency in this soil, overcoming detection limit issues usually accompanying such low levels of Zn. This method also provides that potential to assess other micronutrients ( Mn, Cu ) and with further modification potentially assess K. Before DGT can become established as an alternative soil testing method, validation of the performance is required under field conditions. This study has shown that it out performs current common soil testing methods in glasshouse conditions but questions still remain if this will be reflected out in the field.
Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2007.

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Mason, Sean David. "Diffusive gradients in thin films (DGT) as a technique to predict nutrient availability to plants". Thesis, 2007. http://hdl.handle.net/2440/57973.

Texto completo

Resumen

The soils of Australia have extensive macro and micronutrient disorders varying greatly in their capacities to provide the chemical nutrients essential for plant growth. Assessment of nutrient availability in soils is important in order to maximise fertilizer efficiency and crop yields and to minimise environmental pollution associated with over fertilisation. Nutrient availability has proven difficult to assess due to the complexity of trace element soil chemistry and plant uptake mechanisms. The relatively new method, Diffusive Gradients in Thin Films ( DGT ), provides the potential to become an alternative soil test that could accurately predict nutrient availability. To date, DGT technology has only been designed for separate assessment of anionic and cationic species in waters or soils typically at concentrations characteristic of highly contaminated systems. In this study a new mixed binding gel ( MBL ) was developed capable of simultaneous assessment of cations and anions in a single assay at concentrations more representative of uncontaminated agricultural soils, sediments and waters. The MBL has the potential to eliminate measurement errors associated with very fine spatial scale changes in element concentrations in these environments. The MBL consisted of ferrihydrite and Chelex - 100 cation exchange resin combined together in a binding gel. Results from the MBL were comparable to experiments performed using individual Chelex gels and ferrihydrite gels that have been shown to work successfully for DGT methodology. To facilitate combined analysis of P and cations by ICP - MS, HCl ( 1 M ) was used for gel elution to minimise interferences from [superscript 14] N [superscript 16] OH or [superscript 15] N [superscript 16] O on [superscript 31] P. All elements tested ( Cd, Cu, Mn, Mo, P and Zn ) were bound successfully to the MBL. DGT measurements obtained using the MBL on agricultural soils correlated well ( r ? = 0.95 ) with measurements obtained using pure Chelex and ferrihydrite binding layers. This suggests that the MBL could be used for simultaneous measurement of cationic and anionic element availability in soils. Performance of the Diffusive Gradient in Thin Films ( DGT ) technique was compared with three other common testing methods ( Colwell, Olsen, Resin ) for available soil P in terms of the ability of each to predict wheat, canola, lupin and barley responsiveness to applied P on 21 Australian agricultural soils. DGT accurately predicted plant responsiveness in > 90 % of the soils used. In contrast the other soil testing methods failed to correctly predict plant response to P on numerous occasions. These observations reveal that the DGT technique with the newly developed MBL can predict plant available P on these soils with greater accuracy than other traditional soil P testing methods and could become a useful tool for predicting P fertilizer requirements. The DGT method using the MBL was also used to test Zn deficiency thresholds for canola and wheat in a manufactured soil ( acid washed sand ). DGT successfully determined the threshold for Zn deficiency in this soil, overcoming detection limit issues usually accompanying such low levels of Zn. This method also provides that potential to assess other micronutrients ( Mn, Cu ) and with further modification potentially assess K. Before DGT can become established as an alternative soil testing method, validation of the performance is required under field conditions. This study has shown that it out performs current common soil testing methods in glasshouse conditions but questions still remain if this will be reflected out in the field.
Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2007.

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Zhang, Yulin. "Development of the diffusive gradients in thin films (DGT) technique for plant available potassium measurement in Australian soils". Thesis, 2015. http://hdl.handle.net/2440/104747.

Texto completo

Resumen

Potassium (K) is an essential plant macronutrient and the most abundant cation found in plants. Except for nitrogen (N), K is taken up by plants more than any other nutrient from the soil (Havlin et al. 2005). Due to the complexity of the plant K uptake process, which is affected by multiple factors, the traditional soil K testing methods (e.g. CaCl₂ K, Colwell K, NH₄OAc K, etc.) have generally failed to provide an accurate indication of the amount of K fertilizer should be applied before planting. Beyond measurements of bioavailable fractions of trace elements, the relatively new diffusive gradients in thin films (DGT) method has successfully predicted plant-available phosphorus (P) in agricultural soils. As the main mechanism of K uptake by plants is by diffusion, which is the same mechanism of P uptake by plants, it is likely that the DGT could provide an accurate prediction of plant K requirements. The DGT K method has been improved to enable measurement of both plant-available P and K in soils by using a new mixed Amberlite and ferrihydrite (AMF) gel. Compared to the resin gel used by Tandy et al. (2012), the MAF gel has improved properties in terms of Amberlite distribution resulting in a flat shape, which avoids the difference in length of K⁺ diffusion pathways caused by unevenly-distributed Amberlite particles in the gel and aids in the process of preparing the DGT devices. With the new resin gel, it was revealed that the DGT method can be used at longer deployment times (>2 h) and was capable of measuring solution concentrations of K larger than 16 mg L⁻¹ - limitations which were reported by Tandy et al. (2012). It was also the first time that the diffusion coefficient of K through the diffusive gel was fully investigated in the presence of competing cations (e.g. Ca²⁺, Mg²⁺ and NH₄⁺). Since the MAF gel incorporates ferrihydrite, which is traditionally used for P measurement using the DGT method, the MAF gel was shown to have the ability to measure both P and K in solution and in soils, compared with the traditional gel containing ferrihydrite alone. Besides having the ability to take up K, the MAF gel also has the ability to bind calcium (Ca) and magnesium (Mg) from solution. With the measurement of elution and uptake efficiencies of the MAF gel for Ca and Mg and the diffusion coefficients of Ca and Mg through the diffusive gel, the DGT method can also be used to measure the available of Ca and Mg in solution and soil environments. Due to higher affinity of the MAF gel for Ca and Mg compared to K, measurement of available K in soil using the DGT method is mainly restricted by Ca, the main competing cation present in agricultural soil solutions. In some scenarios, high Ca concentrations in soils mean that shorter deployment times must be used or else measurements of K are affected. Larger effects of deployment time on the CDGT of K were observed at shorter deployment times. The effects of thickness of the diffusive gel on the CDGT of K were found to be inconsistent across soils. Finally the accuracy of the DGT K method and the traditional extraction methods for K were compared in terms of predicting wheat growth to K application in soils at two different root densities in a glasshouse trial. For predicting wheat relative yield, the Colwell K and NH₄OAc K methods were more accurate compared than the DGT and CaCl₂ K methods at low root densities, which is the situation most relevant to field conditions. The ability of the DGT K method to predict plant response to K varied with root density, and was poor at low root densities. However, the DGT K method was a good predictor of wheat tissue K concentrations irrespective of root density (R²≥0.84). Further investigation showed that the increases in concentrations of K measured by the DGT method as a function of rate of K fertilizer application were highly (inversely) correlated to the potassium buffering abilities (KBA) of the soils (R²=0.96). KBA may be a good predictor of soils that are potentially prone to depletion of available K and susceptibility to deficiency, as soils with low KBA have a reduced ability to resupply soil solution K pools in response to K removal by plant roots. The DGT K method is not recommended for adoption as a soil test K method for wheat before further evaluation of the performance using crop responses to K in field conditions. There is room for further improvement of the method to measure more strongly bound K in soil which appears to contribute to crop K nutrition, by changes to the binding gel and the diffusive gel in order to obtain more selective uptake of K by the binding gel and potentially change the transport of K through the diffusive gel. As K uptake varies between plant species, the ability of the DGT K method to predict K requirements by other crop types also requires evaluation.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Agriculture, Food and Wine, 2015.

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Chess, Timothy William. "Laboratory optimization and field demonstration of diffusive gradients in thin films for in-situ mercury measurements of river sediments". Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-08-1942.

Texto completo

Resumen

Diffusive gradients in thin film (DGT) technique is applied to determine pore water mercury concentrations in river sediments. DGT devices have been a useful indicator of dissolved metals in aqueous systems, although it is not as well developed for measuring mercury. DGT devices were evaluated for three different ion exchange resins for adsorption of mercury. After a series of laboratory experiments, 3-Mercaptopropyl Functionalized Silica Gel (3M) was chosen as an effective resin layer. Laboratory experiments showed that the resin strongly associated with dissolved Hg²⁺. DGT probes were tested with sediments from the South River (Virginia, USA) in the laboratory and the time dependent deployment verified an uptake of mercury to the probes and established an effective diffusion coefficient for site specific utilization. Multiple piston and sediment probes were deployed in the South River in-situ to determine overlying water Hg concentrations and sediment pore water Hg concentration profiles. The DGT devices were successful in measuring Hg concentrations in-situ.
text

Los estilos APA, Harvard, Vancouver, ISO, etc.

48

(5930279), Yuvraj Singh. "CHARACTERIZATION OF INTERFACIAL ENERGY OF THIN FILMS THROUGH CURRENT INDUCED DIFFUSIVE INTERFACIAL VOIDING". Thesis, 2019.

Buscar texto completo

Resumen

Electromigration in thin films is a well known failure mode for scaled microelectronics. While our understanding of electromigration physics has improved immensely in the last few decades, there are still some gaps in literature. In particular, the influence of interfaces on the mass transport rate is not well understood. Through reliability studies conducted on passivated metals films, marked improvement in electromigration lifetimes was observed. Specifically, some choices of materials for passivation appear to perform better than others. Qualitatively this improvement in electromigration performance is attributed to surface adhesion. However, a theoretical connection is largely missing in the literature. Lane et al. through in-situ electromigration experiments and separate interfacial debond experiments on sandwich specimens showed that a correlation exists between the void growth rate and the debond energy. However, a fundamental understanding of the relation between the two is missing. In this study we explore the connection between interfacial adhesion and void growth in a current driven system. Several experiments with varying test conditions are carried out on Blech-like test structures with different capping layers. The influence of these capping layers is captured through direct void growth measurements. Comparison of activation energy associated with electromigration was made against existing literature. It was found to be consistent with values reported for surface/interface dominated diffusion mechanisms. Further, an extension is proposed to the phase growth relations derived in existing literature to include the effect of surface adhesion. Interfacial adhesion energy ratios are extracted from the electromigration experiments for two of the test structures (Cu-Ta and Cu-SiNx) tested in this study. This ratio is compared to values reported in literature for the two interfaces and they show good agreement with experimental data.

Los estilos APA, Harvard, Vancouver, ISO, etc.

Tesis sobre el tema "Diffusive gradients in thin films"

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros