Evaluating Changes in the Molecular Composition and Optical Properties of Pacific Ocean Dissolved Organic Matter (DOM) caused by Borodeuteride Reduction

Marla Bianca, University of Maryland College Park, Chemistry and Biochemistry, College Park, MD, United States, Neil V Blough, Univ Maryland, College Park, MD, United States, Rossana Del Vecchio, University of Maryland, ESSIC, College Park, MD, United States, Carmen Marie Cartisano, Univeristy of Maryland College Park, Chemistry and Biochemistry, College Park, MD, United States, Philippe Schmitt-Kopplin, Helmholtz Zentrum Muenchen, Research Unit Analytical BioGeoChemistry, Neuherberg, Germany and Michael Gonsior, University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, United States
Abstract:
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) is a powerful tool to obtain detailed molecular information for complex DOM and was combined in this study with optical measurements to determine the molecular fingerprint of Pacific Ocean DOM before and after borodeuteride reduction. Selective chemical reductions, using sodium borodeuteride, has been previously demonstrated to produce unique mass markers of ketone and aldehyde-containing species in ultrahigh resolution mass spectrometry. These functional groups have also been proposed to be responsible for chromophoric dissolved organic matter (CDOM) long wavelength optical properties through charge transfer interactions and their chemical reduction has shown to irreversibly alter the CDOM optical properties. ESI-FT-ICR MS coupled with borodeuteride reduction was thus applied to reference material, Suwannee River Fulvic Acid (SRFA), and CDOM extracts collected from Station ALOHA, in the North Pacific Ocean during December 2014. Results showed distinct differences between samples collected at different depths, indicating that the combination of FT-ICR-MS with borodeuteride reduction is a useful analytical tool to further understand marine DOM molecular composition. When this method is combined with optical measurements, specific insights into the CDOM composition can also be obtained.
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