An ultrahigh-resolution mass spectrometry index to estimate natural organic matter lability
- D'Andrilli, Juliana [ Montana State University: Chemical & Biological Engineering ] [ Center for Biofilm Engineering ]
- Cooper, William T. [ Department of Chemistry & Biochemistry, Florida State University ]
- Foreman, Christine M. [ Montana State University: Chemical & Biological Engineering ] [ Center for Biofilm Engineering ]
- Marshall, Alan G. [ Department of Chemistry & Biochemistry, Florida State University ] [ Cyclotron Resonance Program, National High Magnetic Field Laboratory, Florida State University ]
RATIONALE:Determining the chemical constituents of natural organic matter (NOM) by Fourier Transform IonCyclotron 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 todetermine 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 electrosprayionization at the National High Magnetic Field Laboratory in Tallahassee, Flor ida, was used to validate the application ofa NOM lability index. Solid-phase extraction cartridges were used to isolate the NOM prior to FTICRMS; mass spectralpeaks were calibrated internally by commonly identiï¬ed NOM homologous series, and molecula r formulae weredetermined for NOM composition and lability analysis.RESULTS: A molecular lability boun dary (MLB) was developed from the FTICRMS molecular data, visualized from vanKrevelen 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, morerecalcitrant character. Of all marine, freshwater, and glacial environments considered for this study, glacial ecosystemswere 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 theMLB is useful not only for individual NOM FTICRMS studies, but also provides a lability threshold to compare andcontrast molecular data with other FTICRMS instruments that survey NOM from around the world.