Spelling suggestions: "subject:"aggregate""
151 |
Tratamento superficial dos agregados reciclados de RCD com hidrofugantes. / Surface treatment of CDW recycled aggregates with water-repellents.Santos, Winnie Franco 04 April 2016 (has links)
A proposta busca reduzir a absorção de água dos agregados reciclados de Resíduos de Construção e Demolição (RCD), através do tratamento de sua superfície com hidrofugante, de maneira que estes não aumentem o consumo de água tampouco reduzam a resistência mecânica. Os agregados reciclados de RCD foram caracterizados quanto à granulometria, morfologia, porosidade, ângulo de contato aparente, absorção de água, análise de imagem e rugosidade superficial. Em seguida, os mesmos foram tratados superficialmente com dois tipos de hidrofugante: solução de silano e parafina. Todos os tratamentos permitiram reduzir a absorção de água dos agregados reciclados de RCD. O tratamento por imersão foi aquele que permitiu obter os melhores resultados e a menor variabilidade entre as técnicas. Os tratamentos hidrofugam a superfície, apesar da parafina apresentar maior molhabilidade. O tratamento com parafina apresentou, em termos de absorção de água, resultados inferiores e menos variáveis que o silano. Os parâmetros de rugosidade constataram que, ambos os materiais perdem seu perfil topográfico original quando tratados com parafina. Os diferentes agregados reciclados com cada hidrofugante foram aplicados em materiais cimentícios analisados no estado fresco e no estado endurecido. Os tratamentos reduziram a absorção e o consumo de água de mistura, porém afetaram negativamente as propriedades mecânicas, devido nova interface gerada (no caso específica de parafina) e falta de molhabilidade nas superfícies. / The proposal aims to reduce the water absorption of the Construction and Demolition Waste (CDW) recycled aggregates through hydrophobic surface treatment, so that these do not increase the concretes water consumption (nor reduce de mechanical strength). The CDW recycled aggregates were characterized regarding granulometry, morphology, porosity, apparent contact angle, water absorption, image analysis and surface roughness. Then they had their surface treated with two types of water-repellent: silane solution and paraffin. All treatments have reduced water absorption of the CDW recycled aggregate. Immersion treatment was the one that allowed the best results and the lowest variability between techniques. The treatments repel water on surface, despite the paraffin presenting better wettability. Paraffin treatment showed, in terms of water absorption, lower and less variable results than silane did. Roughness parameters found that both materials lose their topographic profile when treating with paraffin. The different recycled aggregates with each repellent were applied in cementitious materials analyzed in fresh and hardened state. The treatments reduced absorption and mixing consumption of water in the mixing, but adversely affect mechanical properties due to the new interface created (paraffin wax in special) and the lack of wettability on surfaces.
|
152 |
Stabilisation des émulsions laitières aux cours des traitements technologiques : action combinée des agrégats de protéines de lactosérum et des caséines. / Combined effect of whey protein aggregates and caseins on dairy emulsions stability during technological treatments.Chevallier, Marie 10 March 2017 (has links)
Les émulsions laitières sont des systèmes thermodynamiquement instables qui doivent résister aux contraintes technologiques (chauffage, congélation) appliquées lors de leur fabrication ou usage. Les émulsions riches en protéines de lactosérum sont particulièrement sensibles et l’emploi d’additifs alimentaires est un moyen de ralentir leur déstabilisation. Dans l’objectif d’offrir des produits 100 % lait aux consommateurs, concevoir des émulsions, riches en protéines de lactosérum, sans additifs alimentaires et stables aux traitements technologiques, constitue un réel challenge. La stratégie employée dans ce projet de thèse a été de combiner les propriétés des agrégats de protéines de lactosérum et des caséines pour stabiliser des émulsions aux cours des traitements technologiques sur une large gamme de concentration.Des émulsions ont été préparées avec des agrégats de protéines de lactosérum de structure différente et avec différents ratios agrégats/caséines. Quelle que soit leur structure, la présence d’agrégats à la surface des globules gras déstabilise l’émulsion (gélification /séparation de phase) alors que dans la phase dispersante ceux-ci sont stables aux traitements technologiques. A l’inverse, les émulsions dont la surface des globules gras est recouverte de caséines sont très stables aux traitements technologiques. Ainsi, il est possible de moduler la stabilité des émulsions riches en protéines de lactosérum aux cours des traitements technologiques en exploitant les propriétés des agrégats et des caséines et en contrôlant leur répartition entre la surface des glo / Dairy emulsions are thermodynamically unstable systems, which have to be resistant to the technological treatments (heating, freezing/thawing) applied during their manufacture or use. Whey protein-rich emulsions are particularly sensitive to technological treatments and instabilities are currently tackled by the use of non-dairy additives. With aim to offer products that are more natural to consumers (additive-free), the preparation of whey protein-rich emulsions without additive and stable during technological treatments constitutes a major challenge for dairy companies. The strategy adopted during this thesis was to combine the properties of the whey proteins aggregates and caseins in order to stabilize emulsion during technological treatments in a large range of protein concentrationsEmulsions were prepared with various whey protein aggregates and various whey protein aggregates/caseins ratio. Whatever the whey protein aggregates, their presence at the fat droplet surface destabilize the emulsions (gelation/phase separation) whereas they are stable in the continuous phase of the emulsions during technological treatments. In contrast, emulsions are extremely stable during technological treatments when caseins fully cover the fat droplet surface. The results obtained highlighted the possibility of modulating the stability during technological treatments of whey protein-rich emulsions by combining the properties of the whey protein aggregates and the caseins and by controlling their repartition between the fat droplet surface and the continuous phase of the emulsion.
|
153 |
Měnová a finanční statistika v ČNB - statistika peněžních agregátů / Monetary and Financial Statistics in the Czech National Bank - statistics of monetary aggregatesBarkhanskyy, Kostyantyn January 2010 (has links)
This work focuses on the problems of monetary aggregates in the Czech Republic within compilation of balance sheet items statistics of monetary financial institutions. The content of this paper comprises the methodological basis for the compilation of monetary aggregates and the overall balance sheet statistics with focus on detailed description of the procedure of compiling of this statistics in the Czech National Bank. The goal is to provide an overview of the methodology of balance sheet statistics, practical aspects of its composition and compiling of monetary aggregates.
|
154 |
Regulation of proteotoxicity through atypical NEDDylation / Régulation de protéotoxicité via la NEDDylation atypiqueMaghames, Chantal 10 November 2016 (has links)
Les cellules sont constamment exposées à des stress « protéotoxiques » qui altèrent leurs protéines. Si les protéines endommagées ne sont pas réparées ou éliminées, elles peuvent former des agrégats toxiques pouvant conduire à l’émergence de plusieurs maladies, telle que les maladies neurodégénératives et le cancer. Pour éviter cette toxicité, les cellules ont développé plusieurs stratégies qui collaborent et communiquent afin d'assurer le contrôle de qualité des protéines et maintenir l’intégrité du protéome cellulaire. L’ensemble de ces stratégies forment le réseau de l’homéostasie protéique ou « protéostasie ». Ce réseau inclus les chaperonnes moléculaires, les systèmes protéolytiques (lysosomes, protéasomes) et des systèmes de séquestration des protéines endommagées. L’Ubiquitine et les protéines apparentées à l’Ubiquitine telle que SUMO et NEDD8, sont des effecteurs essentiels de ce réseau. Ces molécules modifient leurs substrats de façon covalente, grâce à l’action d’une cascade d’enzymes E1, E2 et E3. En principe, on considérait que chacune de ces voies employait sa propre cascade enzymatique pour la modification post-traductionnelle de ses substrats. L’Ubiquitination joue un rôle essentiel dans la réponse au stress cellulaire, surtout en assurant la dégradation protéasomique des protéines mal repliées. Récemment, notre laboratoire a trouvé que plusieurs stress protéotoxiques telle que l’inhibition du protéasome, un choc thermique et un stress oxydatif, causent une augmentation de NEDDylation. De manière remarquable, cette augmentation ne dépend pas de l’enzyme d’activation de NEDD8 NAE, mais plutôt de celle de l’Ubiquitine Ube1. De plus, elle se caractérise par la formation des chaînes poly-NEDD8 et des chaînes mixtes entre NEDD8 et Ubiquitine. Ce processus est réversible et une restauration cellulaire est obtenue une fois le stress atténué. Le but de notre projet est de caractériser la réponse de NEDD8 au stress cellulaire ou ce qu’on appelle « la NEDDylation atypique » en vue de comprendre son effet biologique pendant ces conditions. Nos résultats montrent que la NEDDylation atypique dépend des protéines de stress Hsp70/90 et qu’elle cible principalement les protéines nouvellement synthétisées et mal repliées. On montre que, suite à leur modification par NEDD8/Ubiquitin, ces protéines sont transloquées du cytosol au noyau, où elles sont dégradées par le protéasome. Cependant, des conditions de stress prolongé causent une atténuation de l’activité nucléaire des protéasomes 26S, ce qui provoque alors l’accumulation des protéines endommagées sous forme d’inclusions nucléaires. Ces dernières sont réversibles et peuvent être éliminées par le protéasome une fois le stress atténué. Afin d’identifier les cibles de NEDD8 dans des conditions de stress, nous avons développé une approche protéomique basée sur une stratégie de mutation ponctuelle (NEDD8R74K). Cette stratégie permet l’identification des sites spécifiques de NEDDylation au sein des protéines cibles. Cette approche en combinaison avec le SILAC a permis l’identification de NEDD8, Ubiquitine, SUMO-2 et les protéines ribosomiques en tant que principales cibles de NEDD8 en réponse au stress. Ce qui était plus intéressant est que, en appliquant l’étude protéomique SILAC, on a pu constater que le rôle essentiel de la NEDDylation atypique est d’induire l’agrégation/séquestration d’un ensemble spécifique de protéines au sein des inclusions nucléaires. De plus, nous avons montré que l’agrégation induite par NEDD8 protège les protéasomes nucléaires d’une sévère déficience et permet une meilleure survie cellulaire pendant le stress. Notre étude présente NEDD8 comme un nouvel effecteur dans le réseau de protéostasie, elle identifie une nouvelle inclusion nucléaire cytoprotectrice et montre que la NEDDylation atypique est essentielle pour la réponse cellulaire au stress. / Cells are continuously endangered by a variety of proteotoxic stresses that cause protein misfolding and accumulation. Defects in repair or elimination of protein damage can lead to the formation of toxic aggregates that have been associated with diseases, such as neurodegenerative disorders and cancer. To prevent this toxicity, cells have evolved multiple quality control processes that interact and cooperate to maintain protein homeostasis leading to cellular fitness. These processes form “the proteostasis network”, and include molecular chaperones, proteolytic machineries (lysosomes, proteasomes) and pathways for protein damage sequestration. One of the main effectors of this network is the Ubiquitin and the Ubiquitin-like molecules, such as SUMO and NEDD8. These molecules covalently modify proteins through the action of E1, E2 and E3 enzymes. Historically, it was believed that each pathway employed its own and unique set of enzymes to post-translationally modify its substrates. Ubiquitination is essential for the cellular response to stress, especially by targeting misfolded proteins for proteasomal degradation. However, we recently discovered that proteotoxic stresses including proteasome inhibition, heat shock and oxidative stress induce a global increase in protein NEDDylation. Surprisingly, this increase does not depend on the NEDD8 activating enzyme NAE, but rather on the Ubiquitin activating enzyme Ube1, and is characterized by the formation of poly-NEDD8 chains and mixed chains between NEDD8 and Ubiquitin. Importantly, this process is reversible and cell recovery is accomplished once stress is alleviated. In this study, we focused on characterizing the NEDD8 response to stress or “atypical NEDDylation” in order to understand its biological relevance under these conditions.Our results showed that atypical NEDDylation depends on Hsp70/90 and targets mainly newly synthesized damaged proteins. We showed that, after their NEDDylation/Ubiquitination, misfolded proteins are progressively translocated from the cytosol into the nucleus for proteasomal degradation. However, upon prolonged stress conditions, the activity of nuclear 26S proteasome is compromised, resulting in the accumulation of these conjugates into nuclear inclusions. These inclusions are reversible and eliminated by nuclear proteasomes once stress is alleviated. In order to identify NEDD8 targets upon these conditions, we developed a proteomic approach based on a point mutation strategy (NEDD8R74K) that enables a site-specific analysis of NEDDylated proteins. This approach in combination with SILAC allowed the identification of NEDD8, Ubiquitin, SUMO-2, and ribosomal proteins as the major NEDD8 targets upon stress. Interestingly, by SILAC proteomics we found that the main function of atypical NEDDylation is to induce the aggregation/sequestration of a specific subset of proteins within the nuclear inclusions. We showed that this NEDD8-induced aggregation protects nuclear proteasomes from a severe impairment and allows a better cell survival upon proteotoxic stress.Our study defines NEDD8 as a new effector in the proteostasis network, identifies a new cytoprotective nuclear inclusion and shows that atypical NEDDylation is essential for the cellular response to stress.
|
155 |
"Desenvolvimento de agregados eletrofundidos para utilização em refratários para a zona de queima de fornos de cimento" / DEVELOPMENT OF ELECTROFUSED AGGREGATES FOR USE IN REFRACTORIES FOR THE BURNING ZONE OF CEMENT KILNSLuis Leonardo Horne Curimbaba Ferreira 24 August 2006 (has links)
Os agregados eletrofundidos são largamente utilizados para a produção de refratários tendo em vista a melhoria geral de propriedades propiciada pelo emprego dos mesmos. Neste trabalho projetaram-se agregados eletrofundidos adequados para aplicação em refratários para a zona de queima de fornos de cimento. Para o projeto dos mesmos foi realizada inicialmente uma avaliação a alta temperatura das reações que ocorrem entre as fases refratárias e as fases presentes no clínquer de cimento Portland, visando identificar os sistemas refratários mais promissores. Em seguida foram realizadas eletrofusões de matérias primas pertencentes a estes sistemas, visando a obtenção de diferentes composições de agregados, cujas características foram avaliadas. A última etapa do desenvolvimento envolveu a escolha de alguns agregados para a formulação de refratários para a zona de queima de fornos de cimento; medindo e comparando as propriedades dos tijolos obtidos com um tijolo refratário padrão de magnésia-espinélio. Agregados pertencentes ao sistema MgO TiO2 CaO, mais especificamente ao triângulo de compatibilidade formado pelas fases MgO Mg2TiO4 CaTiO3, mostraram características adequadas para o desenvolvimento de refratários para a zona de queima de fornos de cimento. / Electrofused aggregates are largely used in refractory production due to the better performance reached when they are employed. In this work electrofused aggregates were designed for application in refractories for the burning zone of cement kilns. Initially reaction evaluation was conducted aiming the identification of the most prone refractory systems when single refractory phases react with Portland cement phases at high temperatures. In the next step, raw materials of the best refractory systems were electrofused to generate different aggregate compositions. The electrofused aggregates properties were evaluated and the classified ones were used to produce refractory bricks for the burning zone of cement kilns. General characteristics of these bricks were measured and compared with a standard magnesia-spinel refractory. Aggregates of the system MgO TiO2 CaO, more specifically aggregates belonged to the compatibility triangle MgO Mg2TiO4 CaTiO3, showed suitable characteristics for development of refractories for the burning zone cement kilns.
|
156 |
Study of the mechanical properties of the granitoid rocks and the influence of blasting parameters on the quality of aggregates : Literature ResearchKondelchuk, Dimitry, Novikov, Evgeny January 2005 (has links)
In order to carry out blasting operation with optimal results the influence of rock properties on fragmentation process and the quality of the aggregates should be studied with the proper thoroughness. Recent investigations of granitoid rocks infer that the resistance of rock to abrasion improves with increasing amount of quartz and feldspar. The increasing amount of mica results in the opposite effect. The resistance of granite to the impact effects improves with the increasing amount of mica and decreasing content of feldspar. Another finding states that flakiness positively influenced by the frequency of micro cracks, on the other hand, the increasing micro cracks frequency negatively affects on the rock strength. For practical reasons it can be concluded that safety blasting decreases the propagation of micro cracks, hence improves the quality of the rock material. To obtain desired quality of aggregates the blasting parameters and the types of explosives should be properly considered. This thesis work presents the review of the modern literature concerning the blasting operations and aggregates production. It combines both theoretical and practical parts. It describes the petrographical and mechanical properties of the granitoid rocks, different laboratory tests for mechanical properties and results, types and features of explosives, the parameters that intervene in blast designing and influence of blasting on rock aggregates. The rock mass properties greatly affect the blasting results and the quality of aggregates. However, it’s hard to extend this conclusion on full-scale blasting operations in mines and quarries, because the nature and properties of the rock mass change significantly over the short distances. / <p>Validerat; 20101217 (root)</p>
|
157 |
Soil Aggregates: The mechanistic link to increased dissolved organic carbon in surface waters?Cincotta, Malayika 01 January 2018 (has links)
Dissolved organic carbon (DOC) plays an important role in the global carbon (C) cycle because increases in aqueous C potentially contribute to rising atmospheric CO2 levels. Over the past few decades, headwater streams of the northern hemisphere have shown increased amounts of DOC coinciding with decreased acid deposition. Although the issue is widely discussed in the literature, a mechanistic link between precipitation composition and stream water DOC has not yet been proposed.
In this study, the breakup of soil aggregates is hypothesized as the mechanistic link between reduced acid deposition and DOC increases in surface waters. Specific hypotheses state that soil aggregate dispersion (and the ensuing release of DOC from these aggregates) is driven by a decrease in soil solution ionic strength (IS, decreasing the tendency of flocculation) as well as a shift from divalent to monovalent cations (reducing the propensity for cation bridging) in soil solution.
These hypotheses were tested on soil samples collected from several riparian zone and hillslope positions along three flagged transects in the acid-impacted Sleepers River Research Watershed in northeastern Vermont. To determine soil C content by landscape position, samples from transects spanning hilltop to hillslope and riparian area, as well as replicated hillslope and riparian samples (n=40) were analyzed. Aqueous soil extracts simulate the flushing of soils during hydrologic events (e.g. rain or snowmelt) and were used to test the effect of soil solution chemistry on DOC release. Extracts were prepared with solutions of varying IS (0-0.005M) and composition (CaCl2 and NaCl) on replicated soil samples (n=54) and changes in DOC release and aggregate size were monitored. As IS of the extraction solution increased, the amount of DOC in solution decreased, and aggregate size increased. This was presumably due to cations bridging and diffuse double layer effects. This effect was reversed in low ionic strength solutions where DOC release was significantly higher and average aggregate size was smaller. While extraction solution controlled the amount of C liberated, landscape position impacted the quality, but not quantity, of released DOC.
This study is the first to propose a mechanistic link observed changes in DOC in surface waters and recovery from acidification and provides initial experimental evidence that soil aggregates indeed play a role in the generation of DOC.
|
158 |
Adhesion of bituminous and cementitious materials using Particle-Probe Scanning Force MicroscopyLi, Yujie 01 January 2019 (has links)
As the most important materials in civil engineering, bituminous and cementitious materials have been used widely in pavements and constructions for many years. Accurate determination of adhesion is important to the bonding properties of bituminous and cementitious materials. In this work, we presented a novel approach to measure the adhesion between binders and aggregate mineral particles at microscopic scale.
Particle probe scanning force microscopes (SFM) were used to study the adhesion between mineral microspheres representing the primary aggregate constituents (Al2O3, SiO2 and CaCO3) and various control (PG 64-22 and PG 58-22) and modified binders. Results showed that these modified SFM probes could effectively measure the adhesion between binders and aggregate minerals. Consistent adhesion measurements were obtained between different asphalt binders and aggregate mineral particles. Statistical analyses were performed to evaluate effects of different factors on the aggregate-modified binder adhesion, including aggregate constituents, binder types, modifier types and cantilever properties. Due to the stronger polarity of alumina particles, stronger interactions occur within alumina-binder pairs than within silica- and calcium carbonate-binder pairs. Meanwhile, morphologies of different modified binders clearly demonstrated microstructural variations in these binders.
The adhesion between steel and different cement hydrated products was measured using particle probe SFM. Adhesive forces are collected between steel microspheres and new (four-week old) and old (six-month old) cement in air and saturated lime water. Mixed Gaussian models were applied to predict phase distributions in the cement paste, i.e., low density C-S-H, high density C-S-H, CH, other hydrated products and the unreacted components. For new cement in saturated lime water, adhesive forces between steel and low density C-S-H, high density C-S-H and other hydrated products are intermediate among all groups selected. The adhesive forces between steel and calcium hydroxide are smallest, whereas the adhesive forces between steel and the unreacted phases are largest. For the six-month old cement, the interweaving of calcium carbonate crystals and C-S-H during the carbonation produces greater adhesive forces to steel, consistent with the adhesive forces between steel and the control calcium carbonate specimen. CH turned into calcium carbonate by reacting with carbon dioxide in air. An increase in adhesive forces was found between steel and calcium carbonate in the old cement than those between steel and CH in the new cement.
Particle probe SFM is able to measure the adhesion in bimaterials. For bituminous materials, this methodology provides opportunities to evaluate the effects of different processing methods and to generate quantitative information for the development of multi- scale asphalt mixture cracking models. For cementitious materials, these studies opened new avenues to study the interactions between steel and cement at microscale under a variety of environmental conditions and can be formulated as crack initiation and propagation criteria incorporated in multiscale models for reinforced concrete structures.
|
159 |
From soilscapes to landscapes: a landscape-oriented approach to simulate soil organic carbon dynamics in intensely managed landscapes (IMLS)Wacha, Kenneth Michael 01 January 2016 (has links)
The primary objective of this research was to develop a landscape-oriented, process-based approach that can enhance understanding and prediction of SOC fluxes in IMLs by incorporating the key mechanisms impacting soil carbon dynamics when moving from the soilscape to the landscape. The mechanisms that are considered to be the focus of this study are redistribution of SOC due to erosion and deposition without neglecting the importance of litter incorporation into the soil column, decomposition due to microbial activity, and physical and chemical stabilization of carbon. To accomplish this objective, field experiments were performed to examine how selective entrainment of different soil size fractions, quantified through the enrichment ratio (ER), varies with management and hillslope position. Differential modes in soil mobilization between rill and interrill areas were either elevated or dampened depending on the prevalent management practice, the gradient of the site and landscape position. Sites where sediment and runoff fluxes were highest were found to have lower ER values (around unity) due to the mobilization of all size classes making static and dynamic samples almost identical.
The size fractions analyzed in these experiments were found to have varying levels of carbon associated with them, especially the larger aggregates, which encapsulate organic material. Neglecting them in transport estimates could lead to large errors in predicted fluxes of SOC. For this reason, a careful attention was placed on identifying how aggregate stability varies with respect to management and hillslope position, through controlled experiments looking size distributions to reflect tillage disturbance and aggregate stability to assess resistance to rainsplash.
Lastly, a landscape-oriented modeling framework was developed that captures not only the SOC spatial heterogeneity in IMLs but also determines the impacts that redistribution has on this heterogeneity and ultimately on SOC dynamics. The integrative modeling framework considers the collective effects of both rainsplash/rainfall- and tillage-induced erosion on SOC redistribution in IMLs through an ER-module developed and woven within this framework to connect an upland erosion model with a soil biogeochemical model. It provides not only size fraction updates to the active layer and ER values, but also explicitly considers the effects of splash-driven interrill erosion on those ER estimates.
The model was applied to twentieth-century changes in SOC across a representative agricultural hillslope in the study watershed and compared to recent SOC data. The chronosequence in SOC storage within the erosional zone revealed that soils were continually depleted of the rich organic matter long after the 1930’s “Dust bowl” due to enhanced erosion that accompanied agricultural practices. However, conservation tillage and enhanced crop production that began in the late 1980’s reversed the downward trend in SOC losses, causing nearly 26% of the lost SOC to be regained. Results from this study can be used to aid policy and decision makers in developing a food-system that accounts for the co-evolution of human and natural activity, to develop sustainable agro-ecosystems through the use of data supported recommended best management practices.
|
160 |
Glutamic Acid Resorcinarene-based Molecules and Their Application in Developing New Stationary Phases in Ion ChromatographyPanahi, Tayyebeh 01 June 2016 (has links)
Resorcinarenes can be functionalized at their upper and lower rims. In this work, the upper rim of a resorcinarene was functionalized with glutamic acids and the lower rim was functionalized with either methyl or undecyl alkyl groups. The cavitands were characterized by nuclear magnetic resonance (NMR), mass spectrometry (MS), UV-vis spectroscopy, dynamic light scattering (DLS) and electron microscopy. The binding of resorcinarene with amine guests was studied in DMSO by UV-vis titration. The obtained binding constants (K values) were in the range of 12,000-136000 M-1. The resorcinarenes were shown to form aggregates in a variety of solvents. The aggregates were spherical as confirmed by DLS, SEM and TEM experiments. Dynamic light scattering (DLS) experiments revealed the size of the aggregates could be controlled by cavitand concentration, pH, and temperature. The resorcinarene with undecyl alkyl group were adsorbed onto 55% cross-linked styrene-divinylbenzene resin to prepare a new stationary phases for ion chromatography (IC) columns. The new column packing material was applied in determination of uremic toxins and water contaminants. The new IC column afforded separation of the five uremic toxins : guanidinoacetic acid, guanidine, methylguanidine, creatinine, and guanidinobenzoic acid in 30 minutes. Detection and quantification of uremic toxins helps diagnose kidney problems and start patient care. Gradient elutions at ambient temperature with methanesulfonic acid (MSA) as eluent resulted in detection levels in water from 10 to 47 ppb and in synthetic urine from 28 to 180 ppb. Trace levels of creatinine (1 ppt) were detected in the urine of a healthy individual using the columns. The new IC stationary phase separated cationic pharmaceuticals including a group of guanidine compounds in surface water. Detection limits in the range of 5 - 32 µg L-1 were achieved using integrated pulsed amperometric detection (IPAD) for guanidine (G), methylguanidine (MG), 1,1-dimethylbiguanidine (DMG), agmatine (AGM), guanidinobenzoic acid (GBA) and cimetidine (CIM). Suppressed conductivity (CD) and UV-vis detection resulted in limits of detection similar to IPAD, in the range of 1.7 - 66 µg L-1, but were not able to detect all of the analytes. Three water sources, river, lake, and marsh, were analyzed and despite matrix effects, sensitivity for guanidine compounds was in the 100 µg L-1 range and apparent recoveries were 80-96 %. The peak area precision was 0.01 - 2.89% for IPAD, CD and UV-vis detection.
|
Page generated in 0.0413 seconds