Browsing by Author "Marshall, Alan G."

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Characterization of IHSS Pony Lake fulvic acid dissolved organic matter by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and fluorescence spectroscopy
(2013-12) D'Andrilli, Juliana; Foreman, Christine M.; Marshall, Alan G.; McKnight, Diane M.
We present the extensive characterization of Antarctic Pony Lake (PL) dissolved organic matter (DOM), an International Humic Substance Society (IHSS) fulvic acid (FA) reference standard, using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and excitationâ€“emission matrix fluorescence spectroscopy (EEMS). PLFA is the first reference standard available through IHSS derived solely from a microbial source. A number of factors differentiate PLFA from other IHSS standards, including source material, geographic location, sunlight exposure, freezeâ€“thaw conditions, and other in situ environmental influences. ESI FT-ICR MS and EEMS were used to compare the PLFA microbial DOM compositional signature with the IHSS Suwannee River (SR) FA, a standard frequently studied for environmental DOM analysis. Although CcHhOoNnSs(n = 0, 1, or 2 and s = 0 or 1) constituents were present in both IHSS samples, PLFA contained more N and S molecular species, whereas SRFA was dominated by CcHhOo compounds. Proteinaceous character was detected with both methods, in greater abundance for PLFA, which we attributed to its microbial source material and labile, potentially more reactive nature than SRFA. Characterization from both analytical techniques resulted in complementary data that reinforce the importance of PLFA as an IHSS reference standard that should be utilized for other microbiological environmental DOM comparisons.
An ultrahigh-resolution mass spectrometry index to estimate natural organic matter lability
(2015-12) D'Andrilli, Juliana; Cooper, William T.; Foreman, Christine M.; Marshall, Alan G.
Rationale: Determining the chemical constituents of natural organic matter (NOM) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICRMS) remains the ultimate measure for probing its source material, evolution, and transport; however, lability and the fate of organic matter (OM) in the environment remain controversial. FTICRMS-derived elemental compositions are presented in this study to validate a new interpretative method to determine the extent of NOM lability from various environments. Methods: FTICRMS data collected over the last decade from the same 9.4 tesla instrument using negative electrospray ionization at the National High Magnetic Field Laboratory in Tallahassee, Florida, was used to validate the application of a NOM lability index. Solid-phase extraction cartridges were used to isolate the NOM prior to FTICRMS; mass spectral peaks were calibrated internally by commonly identified NOM homologous series, and molecular formulae were determined for NOM composition and lability analysis. Results: A molecular lability boundary (MLB) was developed from the FTICRMS molecular data, visualized from van Krevelen diagrams, dividing the data into more and less labile constituents. NOM constituents above the MLB at H/C ≥1.5 correspond to more labile material, whereas NOM constituents below the MLB, H/C <1.5, exhibit less labile, more recalcitrant character. Of all marine, freshwater, and glacial environments considered for this study, glacial ecosystems were calculated to contain the most labile OM. Conclusions: The MLB extends our interpretation of FTICRMS NOM molecular data to include a metric of lability, and generally ranked the OM environments from most to least labile as glacial > marine > freshwater. Applying the MLB is useful not only for individual NOM FTICRMS studies, but also provides a lability threshold to compare and contrast molecular data with other FTICRMS instruments that survey NOM from around the world.