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To better constrain the chemical composition and molecular diversity of dissolved organic matter (DOM) in natural waters, comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOF-MS) was applied for the first time as a novel technique towards its characterization. This technique chromatographically resolved thousands of peaks per sample and yielded a level of chromatographic resolution that approached the effective mass resolving capabilities of Fourier transform ion cyclotron resonance mass spectrometers (FT-ICR-MS). As with peaks resolved by FT-ICR-MS, the chemical identities of peaks resolved by GCxGC-TOF-MS (> 90 %) remained largely unknown, however GCxGC-TOF-MS provided an independent means by which peaks could be tied to known compounds, which included (1) electron-impact mass spectra accompanying each peak and (2) the separation of structurally related compounds along predictable trajectories in two-dimensional GCxGC space. The development and implementation of this methodology (Chapter II) identified 451 compounds across diverse CuO- oxidized, TMS-derivatized samples and provided a basis for identifying 313 compounds (6.5 % of peaks) within a solid phase extracted (SPE) DOM sample isolated from the Upper Truckee River, Lake Tahoe, California, USA. This represented the most comprehensive compound-specific characterization of a DOM sample to date and an approximate three-folding of compounds previously identified within this oxidation product mixture, a subject of three decades of extensive study. Novel compounds were discovered, isothermal retention in the second dimension was predicted using molecular mechanics modeling, and evidence for a previously unexplored isomeric diversity within DOM was presented. Thousands (> 90 %) of GCxGC-resolvable peaks, however, resisted facile structural elucidation and motivated the development and implementation of a methodology (Chapter III) by which the chemical distance between specific peak populations (defined by chromatographic localization and peak intensity) of two samples could be quantified. Performed pair-wise across a sample set of Lake Tahoe Basin SPE-DOM samples, distance matrices amenable to linkage analysis were constructed, hierarchical relationships of similarity between peak populations were exposed, and cluster analysis identified sample groupings that were subsequently corroborated by high resolution proton nuclear magnetic resonance spectroscopy (¹H-NMR) of CuO- oxidized DOM. Interpretively revealing results were obtained, including the likely identification of peak populations specific to degraded terrestrial OM. In Chapter IV, a 13,500-year organic geochemical record ([delta]¹³C, [delta¹⁵N, TOC, TN, C:N) spanning the Holocene was created for Fallen Leaf Lake (FLL), California Sierra Nevada, USA. This was complemented by a 4,500-year lignin phenol record which spanned the Pleistocene-Holocene transition. These records were interpreted within the context of Holocene climate and seismicity and a post-glacial history of flora succession was proposed. In Chapter V a newly developed, high resolution, two-dimensional, heart-cutting preparative capillary gas chromatograph (PCGC) was developed, applied, and successfully evaluated as a tool for the enrichment of &mug quantities of material destined for natural abundance radiocarbon (¹⁴C) analysis by accelerator mass spectrometry (AMS) |
