Fourier Transform Mass Spectrometry for the Molecular Level Characterization of Natural Organic Matter: Instrument Capabilities, Applications, and Limitations

Abstract

All living matter in the environment (i.e., animals, plants, microorganisms, etc.) eventually dies and decomposes into what is known as natural organic matter (NOM). NOM is formed from a vast variety of sources that have been chemically or microbially degraded in the environment where they arise, and NOM can be generally described as a complex mixture of organic compounds (Stevenson, 1994). Within this mixture, some compounds retain their individual reactivity and characteristics, while others tend to aggregate together and act as a polymeric unit. Overall, NOM can encompass a variety of natural biomolecules, such as lipids, peptides/protein, amino-sugars, carbohydrates, lignins, tannins, and condensed aromatics. Because NOM is a random assortment of organic constituents, its size, shape, concentration, and other physico-chemical properties vary greatly with location and season. For these reasons, the molecular level characterization of NOM continues to be one of the greatest challenges to modern analytical chemists. NOM is ubiquitously present in all natural waters, soils, sediments, and air, giving NOM a central role in numerous environmental processes. These processes are linked together by the global carbon cycle, which describes the storage and flux of carbon sources and sinks throughout the environment (Thurman, 1985; Eglinton and Repeta, 2003; Perdue and Ritchie, 2003). Special attention is generally paid to land-sea interfaces, atmosphere-sea interfaces, and long-term carbon burial/storage. NOM in soils affects the cation exchange capacity and water retention of soils, which has triggered studies by the agricultural communities. Furthermore, NOM in soils/sediments influences carbon sequestration and burial, and this carbon is altered over long periods of time and can be transformed to petroleum precursors. NOM in soils and rivers can affect the solubility, transport, and eventual fate of anthropogenic pollutants. These hydrophobic organic contaminants can interact and bind with NOM in the environment, making it difficult to trace throughout the river systems that eventually lead to the ocean. The amount of carbon in dissolved organic matter (DOM) in the ocean is approximately the same as that of atmospheric CO2 (Hedges, 1992; Eglinton and Repeta, 2003) and this exchange has been directly linked to climate change (Canadell et al., 2007; Sabine and Feely, 2007). NOM in the atmosphere can exist as an aerosol or particulate, which impacts human health, climate, and overall air quality. The