Novel ionization methods for characterization of natural organic matter by Fourier transform ion cyclotron resonance mass spectrometry

Natural organic matter (NOM) exists as a highly functionalized, polydisperse and complex mixture of organic compounds derived from decaying plan and animal detritus. NOM has been characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for approximately the past 10 years. Over that time advancements in transfer optics and ICR cell technology have resulted in improvements in sensitivity, dynamic range, mass accuracy, and signal-to-noise; however, ionization techniques for NOM characterization have not improved significantly. Typically, NOM is ionized by negative ion electrospray (ESI). ESI is amenable to NOM characterization because the majority of NOM is highly polar; however, important fractions of NOM are not ionizable by ESI and are therefore remain uncharacterized at the molecular level.;The work presented is devoted to novel ionization methods for two of the most under characterized fractions of NOM by FT-ICR MS. Dissolved organic nitrogen (DON) may be selectively ionized by positive ion atmospheric pressure photoionization. Typically, DON is not characterized by FT-ICR MS because ESI does not efficiently ionize DON relative to the C, H, and O component of NOM. Black carbon, including biochar may be ionized by desorption atmospheric pressure photoionization. Biochar has defied molecular level characterization by FT-ICR MS because, as temperature of thermal degradation increases, the solubility of char in common solvents decreases.;Chapter 1 is a brief introduction to natural organic matter including a short overview of two major components of DOM that remain largely uncharacterized at the molecular level, dissolved organic nitrogen and black carbon. Chapter 2 is a brief introduction to FT-ICR MS principles and establishes why FT-ICR MS is necessary for characterization of complex mixtures such as DOM.;In Chapter 3, positive ion APPI is established as a selective ionization method for DON. DON has an important role in biogeochemistry; however, it remains largely uncharacterized by FT-ICR MS due to inefficient ionization relative to dissolved organic carbon (DOC). Positive ion APPI dramatically increases S/N of DON ions compared with negative ion ESI. Extensive molecular characterization of DON may now be conducted, including tandem mass spectrometry to reveal structural information about DON ions of a single m/z.;Chapter 4 and 5 are applications of positive ion FT-ICR MS for characterization of wastewater-derived DON before and after treatment by advanced oxidation processes and algal remediation, and characterization of DON treated by microbes. An important factor in the bioavailability of organic nitrogen is composition. Large, aromatic compounds that are not available to algae for uptake in the untreated sample are degraded to more labile compounds that are bioavailable. Furthermore, labile DON may be used by microbes and converted to refractory compounds.;Chapter 6 focuses on biochar, an important natural product for the agricultural and fuel industries. Black carbon also represents a significant long-term sink for atmospheric carbon. Characterization of biochar is important for understanding how it interacts in the environment. Many questions are yet to be answered about how char is degraded after initial formation. To date, only the water-soluble fraction of char is characterized at the molecular level by FT-ICR MS. As the temperature of char formation increases, chars become insoluble in common solvents. In Chapter 5, the implementation of desorption atmospheric pressure photoionization (DAPPI) to characterize intact chars is described. DAPPI is an ambient ionization method that does not require sample preparation or separation. The elemental composition of a parent oak, oak combusted at 250 °C, and oak 400 °C are determined by DAPPI coupled to FT-ICR MS. The data show the parent material is mostly composed of lignin- and cellulose-like compounds. As the oak is thermally degraded, the compounds become more aromatic. At 400 °C the oak has lost all of its original identifiable components and is composed of mostly aromatic compounds.