• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 32
  • Tagged with
  • 32
  • 32
  • 32
  • 32
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Schnelle Fraktionierung von Analyt und Probenmatrix in der ETAAS / A Rapid Fractionation of Analyte and sample matrix in ETAAS

Berkhoyer, Yevgen 25 July 2005 (has links)
<br>A recently developed two-stage Atomizer of I. L. Grinshtein was studied. His advantages and disadvantages were discussed. An attempt of the generalization of rapid chromatographical and non chromatographical fractionation of trace elements and sample matrix was carried out for ETAAS successfully. An Electrothermal Flow Fractionation Interface (EFFI) was designed as a development of the ETAAS analysis in order to allow sample preparation and measurement within the ETV system in a carrier gas. All main qualities of the new concept were studied both in theory and practically and compared with results of the conventional techniques as well as with the results of the Grinshtein Atomizer by conventional operation. A new transversally heated graphite atomizer was developed under conditions, that: 1) the lacks of the Grinshtein Atomizer are completely eliminated. 2) his construction is completely compatible to the commercial usual ones and considerably easier than ones of the commercial transversally heated graphite atomizers. 3) all functions of the usual operations such as stages of sample pyrolysis, sample atomization and cleaning of the Atomizer are supported. 4) fractionation of trace elements and sample matrix only due to the atomization process exceed in quality the properties of the usual atomizer operation (see point 3 above). Other numerous improvements of the ETAAS analysis were achieved to. For the first time in the ETAAS history undiluted and concentrated urine was analyzed even without pyrolysis and application of chemical modifiers.
22

Untersuchung der Wechselwirkungen von Mangan- und Calciumionen mit Alginat von Algen und von verschiedenen mucoiden Stämmen des Bakteriums Pseudomonas aeruginosa / Interactions of Calcium- and Manganeseions with algal alginate and alginate from different muciod strains of pseudomonas aeruginosa

Emmerichs, Natascha 31 August 2004 (has links)
In order to obtain detailed information on the interaction of bivalent cations with alginates especially the effects of sequence and acetylation degree the several types of alginates were treated with different solutions of manganese(II)and analysed by 13C-nuclear magnetic resonance (NMR)spectroscopy. The usage of paramagnetic manganese(II) ions lead to a strong influence on the NMR signals of all adjacent nuclei which is based on the dipolar coupling with electron spins of the paramagnetic species. It was found that there are different carbons involved in the interaction of polymannurante and polyguluronate. In alternating sequences the GM/MG parts of the alginates show the strongest interaction with manganese. Additionally it was found that the acetylated parts of the chain show no interaction with the paramagnetic ion. The strong affinity of manganese to the GM/MG-pairs could be a reason for the founded preference of the bacteria to produce alternating alginates. That applies for the amount of the acetyl groups in the alginate. The acetylation degree is another tool to affect the stability of the alginate/cation complexes and therewith for the gelmatrix of alginate/cation gels
23

Development of the Sliding Spark Technique for Trace Analytical Spectroscopy of Dielectric Solid Matrices

Angeyo, Hudson 08 September 2004 (has links)
A novel direct solid-state emission spectroanalytical method based on the pulsed sliding spark source has been developed. The technique is characterised by a radiative transient discharge plasma propagating along the surface of a dielectric solid matrix enforced between a pair of electrodes in air at atmospheric pressure, where matrix excitation is driven by plasma-particle interaction based on geometry- and source opto-electric-modulated electron impact excitation. This dissertation embodies the results of the systematic theoretical and experimental study of the sliding spark which aimed at the analytical development of the technique for trace quantitative spectroscopy of the heavy elements embedded in the dielectric matrix surface layers. The optical emission spectrum, when detected and measured in the wavelength range 212511 nm at about 0.05 nm spectral resolution using optical fibre transmission in conjunction with a holographic blazed grating CCD spectrometer, was found to be suitable for simultaneous multi-elemental analysis. Investigation of the spectral characteristics of several heavy metals embedded in a variety of dielectric matrices (a boro-silicate simulate, borax, polyvinyl-alcohol, cellulose, teflon, Al-Zr simulate ceramic powder, simulate and River sediment samples) has led to the realisation of an empirical scheme for optimal identification and selection of the optically thin lines that are suitable for trace quantitative analysis. The utility of the lines depends on the element and sample matrix. Use of PVC as a matrix modifier results in increased sensitivity through formation of volatile halides. Comprehensive characterisation of the measured spectra provides empirical evidence to exploit the sliding spark at fast pulse frequency also as an atom source for combined emission, fluorescence, and absorption spectroscopy applicable to the elucidation of structural and molecular information by temporal gating, time-resolved techniques. Practical approaches found in the search for an appropriate calibration strategy for quantitative analysis include the use of internal standards based on Y and La (added) and Si and C (matrix-derived) spectral lines, which compensate for the differing ablation yield, signal drifts and matrix effects in and between complex matrices. Accurate analytical models have been derived for Mn, Ti, V, Ni, Co, Cu, Cd, Pb, Cr, Al, Fe, Zn, and Hg. A quantification methodology has been developed based on sediment and as model matrix, which combines high sensitivity and satisfactory reproducibility for Mn, Ti, V, Ni, Co, Cu, Cr, Al, Fe, and Zn. Trace quantitative analysis of dielectric solid matrices by sliding spark spectroscopy is realised in the concentration range from several hundred ppb to thousands of ppm depending on the analyte (and the spectral line utilized) and on the calibration strategy adopted for the quantification. The elemental limits of detection vary from several hundred ppb to few tens of ppm depending on the element, analysed matrix, spectral line, and calibration method. Qualitative speciation analysis is possible for Mn, V, Pb, Ti, Cu, and Co. Sliding spark spectroscopy has been validated as a new, simple but robust and versatile technique for the direct trace analysis of complex solid dielectric and refractory matrices with a reproducibility at 12 %, a precision characterised by a confidence interval of (0.510) %, and an accuracy by relative efficiency of 010 % by the successful analyses of Certified Reference Materials (Stream sediments), sewage sludge, a PVC polymer, an independent XRF laboratory analysis of River Rhine sediment, and by the results of comparative analyses made of the same elements using ICP and XRF (polarised radiation, 3-D Cartesian geometry) techniques.
24

Use of Natural Polysaccharides in Medical Textile Applications

Fouda, Moustafa Mohamed Gaballa El-Sayed 13 September 2005 (has links)
In this thesis chitosan and ß-cyclodextrin were used as candidates in medical textile applications. The antimicrobial activity of dissolved chitosan was evaluated quantitatively against both bacteria and fungi by different methods. The activity increased by increasing the concentration of chitosan. As a result, chitosan was applied as antimicrobial finishing agent to cotton by different anchor groups. Bacterial activity of chitosan-treated cotton was measured by tetrazolium/formazan test method. A water soluble chitosan derivative, namely carboxymethyl chitosan (CMCTS)was synthesized and characterized. CMCTS was applied to pre-cationized cotton forming ionically crosslinked cotton. The improvement in physical properties of cotton combined with a moderate antibacterial activity was achieved. In dentistry, chitosan films were applied to Molloplast® B, soft liner based material for dentures to treat the denture stomatitis. Also ß-cyclodextrin was used in pharmaceutical applications. Two antimycotic drugs were complexed by ß-cyclodextrin. The drug delivery and the solubility of the complexes were measured and evaluated by the laser nephelometry in microtiter plate in-vitro.
25

Darstellung und Untersuchung funktionalisierter Polymeroberflächen / Creating and testing functionalized polymer surfaces

Wittke, Ralph Harald 12 September 2005 (has links)
Different polymers were used as antimicrobial finishing agent in textile application. Different methods were used to functionalize polyvinylamine, chitosan and cylcodextrin onto fibres. The finished fabrics were chracterized by different analytical tools. In addition the antibacterial activity of the modified surfaces was evaluated by Tetrazolium-Formazan test. A surface test agent (Toluol) was complexed by ß-Cyclodextrin and its deliverey was evaluated by olfactometry.
26

Isolierung und Charakterisierung von bakteriellen extrazellulären polymeren Substanzen aus Biofilmen / Isolation and characterization of bacterial extracellular polymeric substances from biofilms

Rode, Alexander 13 September 2004 (has links)
Microorganisms in biofilms are kept together by extracellular polymeric substances (EPS). The EPS are key molecules for the structure, function and organization of biofilms. Chemical and / or physical isolation methods are being used for the quantitative separation of EPS from biofilms. The yield of EPS depends on the method of isolation. Four different methods of EPS isolation were used in this work (separation by stirring and centrifugation, use of a cation exchange resin, extraction with formaldehyde and extraction with formaldehyde and NaOH) on pure culture biofilms of Pseudomonas aeruginosa and biofilms from sewage treatment systems. The isolation by stirring and centrifugation was suitable for pure culture biofilms. If calcium was present in the growth medium stirring and centrifugation alone was not sufficient. The isolation of EPS was successful with the cation exchange method. The method of choice for the isolation of EPS from environmental biofilms was the cation exchange method. EPS from pure culture biofilms of P. aeruginosa and P. fluorescens did not only consist of polysaccharides, but also of significant amounts of proteins. In environmental biofilms humic substances and DNA were found in addition to polysaccharides and proteins. Detailed studies of the EPS from P. aeruginosa showed, that the EPS consisted of 70 % (w/w) of alginate. Alginate showed a clear heterogeneity in relation to charge (acetylated and non-acetylated fraction) and molar mass. Neutral carbohydrates were not found in the EPS after total hydrolysis followed by thin layer chromatography. Proteins amounted to 28 % (w/w) of the EPS. It is assumable that this not only related to enzymes, but also structural proteins (e. g. lectins). Rhamnose lipids (mainly di-rhamno lipid) were also found in the EPS (small amount of 1 % (w/w)); these molecules may also play an important role in the development of the biofilm structure. By increasing the time of biofilm cultivation P. aeruginosa produced (related to cell number) more EPS (mainly alginate). The composition of the EPS was depending on the nutrient medium. In synthetic media high amounts of polysaccharides and almost no proteins (in contrast to rich media) were detected in the EPS. EPS of pure culture biofilms of P. fluorescens contained carbohydrates (57 % (w/w)) and proteins (28 % (w/w)). Acetyl groups (5 % (w/w)) and glucose and galactose after hydrolysis and thin layer chromatography were detected in the EPS. Possibly the exopolysaccharide of P. fluorescens is an acetylated galactoglucan. In the analyzed sludges of waste water treatment proteins followed by carbohydrates made up the main components of the EPS. Humic substances and small amounts of DNA were detected in these EPS. The EPS of aquatic biofilms contained large amounts of humic substances. Uronic acids were not detected in any analyzed environmental biofilm. Therefore acidic polysaccharides in these biofilms cannot play any role in the stabilization of biofilms by cross linking the EPS with multivalent cations. Instead of that, humic substances, nucleic acids and acidic proteins could be responsible for cross linking.
27

Darstellung und Reaktionen einiger ß,Y-ungesättigter Ketone - Preparation and reactivity of some ß,Y-unsaturated ketones

Zinovyeva, Lyudmyla 01 October 2003 (has links)
The reactivity of the polycyclic ß,Y-unsaturated ketones under different conditions were investigated. The titled ketons were reacted with Lithiumaluminiumhidrid and Grignard reagents with following dehydratation of the resulted secondary and tertiary alkohol. The Bucherer reaction, thermolysis and photolysis of these ketones were carried out.
28

Polyelektrolyteigenschaften der gelmatrixbildenden Komponenten von Biofilmen - Polyelectrolyte properties of the gel-matrix building components of biofilms

Kenning, Arnd 01 October 2003 (has links)
Goals of this study are to point out strategies to influence the gel-matrix building components of biofilms. One well characterised component of the extracellular polymeric substances (EPS) of the bacterial strain Pseudomonas aeruginosa SG81 is the alginate AlgSG81. AlgSG81 is one main component of EPS and thus of the gel-matrix, too. AlgSG81 is completely dissociated in aqueous solution and therefore a strong polyelectrolyte (PEL). By means of computation with OSF-theory and validation via viscosity measurements the conformation of AlgSG81-chains in aqueous solution at screened and not screened conditions is that of a coil over a large concentration regime. By addition of tetramethylurea (TMU) to aqueous solutions of AlgSG81 the formation of a physical network (gel) is observed. Different empirical and theoretical approaches to characterise PEL were improved and experimental verified.
29

Dynamical Behaviour of Small Molecules Clathrated in Syndiotactic Polystyrene: a Solid State Deuterium NMR Investigation - Dynamisches Verhalten kleiner Molekülen innerhalb der Hohlräume von syndiotaktischem Polystyrol: eine Deuterium-Festkörper-NMR-Untersuchung

Trezza, Elena 19 November 2003 (has links)
The crystalline regions of the δ-form of syndiotactic polystyrene (s-PS) contain cavities in which certain small molecules can be absorbed. The mobility of six perdeuterated molecules: benzene, toluene, chloroform dichloromethane, 1,2-dichloroethane and 1,2-dibromoethane, present as a guest in these cavities, has been investigated via 2H NMR spectroscopy. For all samples the motional behavior of the molecules absorbed in the amorphous phase of the polymer differs from that shown by the molecules clathrated in the crystalline phase. The motion of all six molecules in the amorphous phase is approximately isotropic at a temperature T = 298 K or higher, but severely anisotropic when the molecules are included in the crystalline phase. The dynamical behavior of each solvent hosted in the crystalline phase of s-PS has been investigated by comparing spectra obtained by simulation of the effect of a certain molecular rotation on the 2H spectra with the experimental spectra.
30

Verkapselung von organischen Substraten in Polycyanoacrylat-Nanokapseln - Encapsulation of Organic Substrates in Polyalcylcyanoacrylate Nanocapsules

Altinbas, Neslihan 21 November 2003 (has links)
In this work, nanocapsules were synthesized from n-butylcyanoacrylat (BCA) and characterized under variation of kind and quantity of the synthesis components. The influences of the quantity variations were interpreted, using a reduced and a complete factorized experimental design. Hereby, the properties of the capsules have been specified, such as width, width distribution, density, wall thickness and morphology of the capsule. For the verification of the construction of the capsules and their characterization different analytical methods have been used, i.e. TGA, TEM, AFM, AUZ and DLS. In addition, Zeta potentials have been measured and taken into consideration.

Page generated in 0.0924 seconds