UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Application of Ultrahigh Resolution Mass Spectrometry and Deuterium Labeling to Determine the Contribution of Ketone/ Aldehyde-Containing Species to the Composition and Optical Properties of Dissolved Organic Matter(2020) Bianca, Marla; Blough, Neil V; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dissolved organic matter (DOM) is a complex, heterogeneous mixture comprised of thousands of chemical species, found in almost all aquatic environments and is one of Earth’s largest carbon reservoirs. DOM is known to affect many biogeochemical processes and may be a crucial component of the global carbon cycle. However, due to the inherent complexity of DOM, understanding and relating its photophysical and photochemical properties to its composition is difficult. This dissertation describes and applies a mass labeling method using ultrahigh resolution mass spectrometry and deuterium labeling to determine the contribution of ketone/ aldehyde-containing species to the composition and optical properties of DOM. Sodium borodeuteride (NaBD4) selectively and irreversibly reduces ketone/aldehyde groups and the changes due to reduction were observed through mass spectrometry and ultraviolet/visible (UV-Vis) and fluorescence spectroscopy. The reduction of ketone/aldehyde-containing species by NaBD4 results in loss of absorption and creates unique mass markers (deuterated species at mass M+3.021927n) in the mass spectrum. The internal consistency of this algorithm for identifying reduced species was tested using two additional methods, both of which resulted in consistently identified reduced species in the mass spectra. This method was applied to Suwannee River fulvic acid (SRFA) with increasing concentrations of NaBD4 to evaluate the extent of reduction which differed depending on the concentration used. Additionally, the extent of reduction resulting from the increasing concentrations of NaBD4, was shown to correlate well with changes in the absorption and emission spectra of the corresponding untreated and reduced samples; thus, providing evidence that ketone/aldehyde functional groups contribute substantially to the bulk optical properties of SRFA. Furthermore, SRFA that was irradiated as well as reduced revealed insights into the structural components in SRFA that were lost or decreased due to irradiation and contributed to the observed optical properties. Also, it was demonstrated that irradiation made terrestrial material appear more like marine DOM. DOM samples from several different aquatic environments were compared using this method to reveal differences and similarities within the composition of DOM. This method has proven to be a useful tool in relating the changes in the optical properties upon the reduction by NaBD4 to the changes observed by mass spectrometry to reveal information on the composition and well as source and structure of DOM.Item A Deuterium Labeling Method for the Characterization of (Chromophoric) Dissolved Organic Matter Using Ultrahigh Resolution Electrospray Ionization Mass Spectrometry(2015) Baluha, Daniel Robert; Blough, Neil; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dissolved organic matter (DOM) is a complex ensemble of naturally occurring organic compounds found in virtually all aquatic environments. The overwhelming diversity of DOM makes it extremely difficult to understand the relationship between its bulk physicochemical properties and its molecular structure and composition. This dissertation describes the development of a novel method to identify ketone/aldehyde-containing species within DOM, which are known to contribute substantially to the ultraviolet/visible (UV-vis) absorption and emission of chromophoric DOM. In this method, an aqueous sample is treated with sodium borodeuteride (NaBD4) and is analyzed via ultrahigh resolution electrospray ionization (ESI) mass spectrometry. Ketone/aldehyde-containing species (at mass m) in the untreated sample are identified by searching the mass spectrum of the reduced sample for peaks corresponding to deuterated derivatives (at mass m+3.021927n). Initial experiments demonstrated that this method reliably discriminates among mass spectral peaks in an untreated DOM sample that comprise species with zero, one, and/or two reducible moieties. The reactivity and optical properties of reducible species within Suwannee River fulvic acid (SRFA) were studied by treating an aqueous sample with several amounts of NaBD4. This study demonstrated that most species with at least one ketone/aldehyde moiety were reduced a single time under low [NaBD4], while higher [NaBD4] resulted primarily in additional reductions on multi-ketone/aldehyde species. Furthermore, the changes in UV-vis absorption and emission of the reduced aliquots relative to that of the untreated were correlated with the number of ketone/aldehyde-containing species reduced and identified by this method. The fully developed protocol was used to compare DOM extracted from several aquatic environments. Two pools of ketone/aldehyde-containing species were tentatively identified: A terrestrially-produced group of lignin/tannin-derivatives and a microbially-produced group of carboxyl-rich alicyclic molecules. While the first pool has previously been shown to contribute substantially to the absorption/emission of chromophoric DOM, the second pool most likely would not. The mass labeling method developed here revealed compositional features that are not observable by common ESI mass spectrometric analyses and may serve as a useful way to link the physicochemical properties of DOM to its structure and composition.