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Zusammenfassung:
Dissolved organic matter (DOM) as a collective term for a very complex mixture of organic compounds in aqueous environments is one of the biggest organic carbon reservoirs on earth. The biggest part of this organic matter is refractory as it is not utilized by microorganisms. Although DOM occurs all over the world and is able to influence the global climate by absorption and release of climate impacting gases it is very little understood. Especially the chemical structures of sulfur containing components in the DOM are unknown. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) as a high resolution technique offers new possibilities in structural analysis of the DOM as it enables the assignment of molecular formulae to thousands of resolved masses. In this study FT-ICR-MS coupled with electrospray ionization (ESI) was used to analyze the sulfur containing components in two different DOM samples, one surface DOM sample from the open North Sea and one deep sea DOM sample from the Pacific Ocean. Three different functional groups were investigated as possible structures of the sulfur containing components in DOM: thioesters, thiols and sulfonic acids. For this purpose all samples were treated with derivatization reagents. Hydrochloric acid was used in the heat for the hydrolization of possibly occurring thioesters and 2-Bromo-1,4-naphthoquinone was used for the reaction with possibly occurring thiols prior to the FT-ICR-MS measurement. The sulfonic acids needed to be analyzed by fragmentation experiments due to their high stability. To verify the results model compounds were analyzed as well. The obtained data of the hydrolysis and the derivatization experiments showed no differences between the spectra prior and after the reaction. As a result, thioesters and thiols can be ruled out as possible structures for the sulfur containing components in DOM. For the fragmentation experiment twelve nominal masses consisting of three homologous series were analyzed. Neutral fragments that are indicators for sulfonic acids were found: SO3, SO2, H2SO3, H2SO4 and CO2+SO3. This confirms sulfonic acids as possible structure for the sulfur containing components in DOM. Further fragments like S1, CSO and CH2S could be found but with varying occurrence in the CH2-homologous series. This might be due to structural differences at least concerning the sulfur containing functional group.
