|The application of ultra-high resolution mass spectrometry (ESI FT-ICR MS) to the structural characterization of marine dissolved organic matter|
Alan Marshall (National High Magnetic Field Laboratory, Florida State University)
Ryan Rodgers (NHMFL)
Mark Behn (WHOI)
The structure and composition of organic matter (OM) plays a critical role in a number of geochemical processes such as metal redox cycling, contaminant transport, and microbial growth and community structure. These processes rely at some point on a reaction between two molecules, e.g., binding of a redox-sensitive metal by an organic ligand or the interaction of an enzyme and a substrate. Thus, understanding the reaction pathways within critical geochemical processes depends on elucidation of the structures of pertinent components within each system. However, in spite of the centrality of organic matter in biogeochemical processes, its composition, sources and fates are often obscure.
Organic matter in aquatic systems is a complex mixture of compounds with diverse functional groups and thus widely varying physico-chemical properties. To date, studies of its composition have relied primarily on gas chromatography (GC) or nuclear magnetic resonance (NMR) spectrometry. Although productive, these techniques have not provided molecular-level composition of polar macromolecules, the primary compounds of OM. The development of ionization sources for polar (ESI), semi-volatile (APCI), and non-volatile macromolecules (MALDI) has revolutionized the ability of geoscientists to examine an increasing fraction of compounds within complex OM mixtures. These ionization techniques have now been applied to the structural characterization of organic acids in drinking water, riverine organic matter and aquatic proteins.
The ability to resolve individual compounds within these mixtures depends on the mass spectrometer used. To date, the best resolution and mass accuracy have been achieved with Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The ultrahigh resolution and mass accuracy of this technique allow detection and identification of thousands of compounds in each sample. After combined external and internal calibration, the mass accuracy is better than 1 ppm, i.e., < 0.001 Da for singly-charged ions of 300 < m/z < 500. Accordingly, elemental formulae can be determined from mass accuracy alone.
This project seeks to extend the applications of FT-ICR MS to complex OM analysis in chemical oceanography. We analyze OM isolated from cultures, coastal and oligotrophic ocean water, and riverine systems. We are developing techniques to analyze the data quickly and accurately.
Funding: National Science Foundation CAREER program; #CAREER-OCE-0529101
Personnel: Krista Longnecker (postdoc)
Publications: (1) E. B. Kujawinski & M. D. Behn. 2006. Analytical Chemistry 78 : 4363-4373; (2) E. B. Kujawinski, K. Longnecker, N. V. Blough, R. Del Vecchio, L. Finlay, J. B. Kitner, and S. J. Giovannoni. 2009. Geochim. et Cosmochim. Acta 73: 4384-4399; (3) Kido Soule, M. C., K. Longnecker, S. J. Giovannoni and E. B. Kujawinski. 2010. Org. Geochem. 41: 725-733; (4) E. B. Kujawinski. 2011. Ann. Rev. Mar. Sci.