Ionotrope Gele von Polyuronsäuren

Ohne Zusammenfassung     

Mass spectrometric characterization of beta-caryophyllene ozonolysis products in the aerosol studied using an electrospray triple quadrupole and time-of-flight analyzer hybrid system and density functional theory

The components of the organic aerosol formed due to gas-phase beta-caryophyllene ozonolysis were characterized by the use of a triple quadrupole and time-of-flight analyzer hybrid system coupled to an electrospray ionization source operated in the negative ion mode. A reversed-phase high-performance liquid chromatography (HPLC) column was used to achieve chromatographic separations at neutral pH which has been proved to induce ionization of organic compounds bearing aldehyde moieties. In addition to the detected oxo- and dicarboxylic acids, isomeric oxidation products, which bear multi-functional groups such as aldehyde, carbonyl and hydroxyl groups, could be differentiated by examining their corresponding collision-induced dissociation (CID) fragmentation pathways. Proposed fragmentation mechanisms were drawn for the experimentally observed fragmentation pathways in all the CID experiments. Cyclic oxidation products could also be discerned and their fragmentation behaviour under low energy collisional conditions was studied in detail. Gas-phase deprotonation potentials were calculated by the use of DFT B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(d) + ZPVE to estimate the most thermodynamically favourable deprotonation site for efficient negative ion formation in the ion source. The optimized gas-phase geometries for the most prominent oxidation products reveal a strong intramolecular interaction between the upper and lower C4 carbon chains, which are formed after the decomposition of the primary ozonide generated by ozone attack of the reactive endocyclic C==C bond.     

A method of calibration of the formic acid monomer concentration in the gas phase

Pyrolysis of t-butyl formate, (CH₃)₃C-O-CHO, has been carried out in a carrier gas stream of Ar or N₂ in a temperature range of 200–400°C. Between 200 and 300°C, the pyrolysis yielded an equimolar mixture of HCOOH and (CH₃)₂C=CH₂. The results have been used as a calibration method for determining the concentration of the gas-phase HCOOH monomer without interference from the formation of the formic acid dimer. Using this technique, the gas-phase infrared absorption cross-section of HCOOH at 1105 cm^–1 (peak to valley) for the resolution of 0.5 cm^–1 has been determined to be 6.76×10^–19 cm² molecule^–1.     

Die schirmwirkung zylindersymmetrischer nichtferromagnetischer körper gegen magnetische wechselfelder

The screening effect of a finite nonferromagnetic symmetric cylinder is investigated theoretically and experimentally. The work is based on the definitions for the screening effect with respect to frequency and phase response. A mathematical solution is obtained by solving the integral equation for the magnetic vector potential. Experimental tests support the theoretical results. It is shown that the short cylinder with certain design parameters provides a far better screening effect (in particular for attenuation peaks) than does a cylinder of infinite length. This applies to certain regions at the cylinder openings. This effect is caused by current displacement in the axial direction.     

Higher order equations related to thin films: Blow-up and global existence, the influence of the initial data

We are interested in the following class of equations:

     

Determination of higher carboxylic acids in snow samples using solid-phase extraction and LC/MS-TOF

The objective of this work was to develop a method to determine the concentrations of higher organic acids in snow samples. The target species are the homologous aliphatic alpha,omega-dicarboxylic acids from C(5) to C(13), pinonic acid, pinic acid and phthalic acid. A preconcentration procedure utilizing solid phase extraction was developed and optimized using solutions of authentic standards. The influences of different parameters such as flow rate during extraction and the concentration of the eluent on the efficiency of the extraction procedure were investigated. The compounds of interest were separated by HPLC and detected by a quadrupole time-of-flight mass spectrometer (qTOF-MS). The recovery rate (extraction efficiency) of the extraction procedure was found to vary between 41% for tridecanedioic acid and 102% for adipic acid. The limits of detection were determined for all compounds and were between 0.9 nmol/L (dodecanedioic acid) and 29.5 nmol/L (pinonic acid). An exception is pinic acid, for which a considerably higher detection limit of 103.9 nmol/L was calculated. Snow samples were collected in December 2006 and January 2007 at the Fee glacier (Switzerland) from locations at heights from 3056 to 3580 m asl and from different depths within the snow layer. In total, the analysis of 61 single snow samples was performed, and the following compounds could be quantified: homologous aliphatic alpha,omega-dicarboxylic acids with 5-12 carbon atoms and phthalic acid. Tridecanedioic acid, pinonic and pinic acid were identified in the samples but were not quantified due to their low concentrations. The three most abundant acids found in the molten snow samples were glutaric acid (C(5)-di; 3.90 nmol/L), adipic acid (C(6)-di; 3.35 nmol/L) and phthalic acid (Ph; 3.04 nmol/L).     

On-line size exclusion chromatography-pyrolysis-gas chromatography-mass spectrometry for copolymer characterization and additive analysis

On-line coupled size exclusion chromatography-pyrolysis gas chromatography mass spectrometry (SEC-Py-GC-MS) is studied as a novel tool for the characterization of complex polymer samples. An automated system for on-line SEC-Py-GC-MS allowing transfer of multiple fractions was developed based on stop-flow operation of the SEC dimension, syringe-based transfer of the SEC fraction to the GC instrument and solvent elimination with subsequent pyrolysis in a programmed temperature vaporization (PTV) injector. After optimization the system was applied to the characterization of a complex terpolymer composed of very similar monomers. The use of the system for combined pyrolysis and additive analyses in polycarbonate was also demonstrated. Results obtained with the new method indicate the interesting potentials of the method for detailed characterization of polymeric materials.