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Wolfgang Schrader

Publications and source records attributed to Wolfgang Schrader.

9 recordsLinked to original sources
PubMed2006

beta-Cyclodextrin as a stationary phase for the group separation of polycyclic aromatic compounds in normal-phase liquid chromatography.

The separation of highly alkylated polycyclic aromatic compounds according to the size of their aromatic system is investigated using the polycyclic aromatic sulfur heterocycles in vacuum gas oil. A large number of reference compounds containing several parent ring systems and different alkylation patterns were first investigated to characterize the retention of polycyclic aromatic compounds likely to occur in high-boiling petroleum samples. A beta-cyclodextrin phase, Merck ChiraDex, was found to be more suitable than chemically bonded aminopropanosilane and tetrachlorophthalimide in normal-phase HPLC with respect to a combination of selectivity towards the number of aromatic double bonds and degree of influence of the alkyl groups of the aromatic compounds. Finally the preseparated polycyclic aromatic sulfur heterocycles from a vacuum gas oil were fractionated according to the number of condensed aromatic rings on the ChiraDex phase and were characterized by Fourier transform ion cyclotron resonance mass spectrometry.

Chromatography, High Pressure Liquid↗
PubMed2006

Monitoring temporal evolution of silicate species during hydrolysis and condensation of silicates using mass spectrometry.

The first stages of solid-state formation from solution can be crucial in determining the properties of the resulting solids. We are trying to approach prenucleation reactions of silicates from an aqueous solution containing tetraalkylammoniumhydroxides (TAAOH) and tetraalkoxysilanes (TAOS) by analyzing hydrolysis and condensation using electrospray mass spectrometry (ESI MS). Time-resolved measurements were performed using different reactor systems to show the stepwise hydrolysis of the silanes and subsequent condensation of silicate monomers via oligomers to form larger units. We approached the precipitation point by varying the pH and the concentrations of the reactants. The results show the evolution of different silicate species occurring during condensation. No defined molecular entities were identified at pH values close to precipitation, which suggests that under the conditions used, solids are probably not formed from defined building blocks.

Journal Article↗
PubMed2005

Studies of complex reactions using modem hyphenated methods: alpha-pinene ozonolysis as a model reaction.

Modern analytical equipment, in this case the combinations of gas chromatography (GC) with mass spectrometry (MS) and infrared spectroscopy (IR) and liquid chromatography (LC) with mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy and infrared spectroscopy, respectively, have been used to monitor complex reactions that do not only form one or two but a larger number of products. Additionally, side reactions of one primary product with a reactant form a second line of secondary products. To be able to propose formation pathways or even mechanistic interpretation of reactions like these, sophisticated analytical instrumentation is necessary to be able to observe all steps of such a reaction. In this case, the gas phase reaction of alpha-pinene with ozone has been used as a model reaction. A number of both volatile and low-volatile reaction products could be characterized and formation pathways for a reaction with ozone and OH radicals were proposed.

Bicyclic Monoterpenes↗
PubMed2005

Characterization of high-molecular-weight sulfur-containing aromatics in vacuum residues using Fourier transform ion cyclotron resonance mass spectrometry.

Millions of tons of vacuum residues are produced in refineries every year and could be a potentially valuable resource for generating electricity and has possible application as heating and marine fuel. In this work, the polycyclic aromatic sulfur compounds (PASHs) from the aromatic fraction of vacuum residue before and after partial hydrodesulfurization (HDS) were derivatized by methylation to the methylsulfonium salts. Fourier transform ion cyclotron resonance mass spectrometry provided high-resolution data on these high-molecular-weight sulfur compounds. Compounds containing one and two S atoms were found to dominate, with masses up to ca. 900 Da. Classification according to hydrogen deficiency and the number of heteroatoms showed extensive series of homologues for double bond equivalents from 5 to 20. The sulfur-containing aromatics were separated using a palladium(II) complex as a liquid chromatographic phase into two compound groups: one containing compounds with an unconjugated thiophene ring and another with a condensed thiophene ring. This, combined with the mass spectrometry (MS) data, allows for the identification of several parent structures. Partial HDS removed primarily compounds with one S atom, whereas those with two S atoms were largely unaffected.

Journal Article↗
PubMed2004

Liquid chromatography/Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR MS): an early overview.

Fourier-transform ion cyclotron resonance mass spectrometry has developed into one of the most powerful analytical techniques. This unique technique enables acquisition of high-resolution mass spectra with high accuracy, which in turn enables determination of the elemental composition of the analyzed compounds. Coupling with liquid chromatography affords a separation technique with a high-resolution "detector" which can be used to investigate very complex matrices. In this review some important instrumental developments are described and applications are presented; these show the advantages and disadvantages of this combination.

Chromatography, Liquid↗
PubMed2004

Longterm results in surgical removal of subfoveal choroidal neovascularization in age-related macular degeneration.

PURPOSE: This study aimed to analyse visual outcome, surgical complications and recurrence rates 3 years after removal of subretinal choroidal neovascularization (CNV) in patients with age-related macular degeneration (AMD). METHODS: The study involved a retrospective analysis of 50 eyes of 50 patients who underwent surgical removal of CNV in AMD between February 1996 and June 1998. The minimum follow-up period was 36 months. Improvement or worsening of visual acuity (VA) was defined as a change of more than two lines. RESULTS: The mean reduction in VA was 2.2 +/- 6.9 lines. Visual acuity improved in 12 eyes, remained stable in 16 eyes and worsened in 22 eyes. Recurrence of CNV occurred in three eyes. CONCLUSION: After surgical excision of age-related subfoveal CNV, VA improved or stabilized in a large group of patients. Considering the development of VA and the low recurrence rate, surgical treatment seems to be beneficial compared to the natural course of CNV over a longterm follow-up of more than 3 years.

Aged↗
PubMed2001

An Analytical Approach for a Comprehensive Study of Organic Aerosols The financial support by the Bundesministerium für Bildung und Forschung and the Senatsverwaltung für Wissenschaft, Forschung und Kultur des Landes Berlin (ISAS Berlin), and the Ministerium für Schule, Wissenschaft und Forschung NRW (ISAS Dortmund) is gratefully acknowledged. The authors want to thank U. Marggraff and W. Nigge (Dortmund) for assistence during MS measurements and Dr. R. Köppe (Univ. Karlsruhe) and Dr. H. Sievers (GSG Karlsruhe) for assistance in FT-ICR-MS measurements.

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Journal Article↗