Synchrotron-Based Mass Spectrometry to Investigate the Molecular Properties of Mineral–Organic Associations

Abstract

Soil organic matter (OM) is important because its decay drives life processes in the biosphere.Analysis of organic compounds in geological systems is difficult because of their intimate association with mineral surfaces. To date there is no procedure capable of quantitatively separating organic from mineral phases without creating artifacts or mass loss. Therefore, analytical techniques that can (a) generate information about both organic and mineral phases simultaneously and (b) allow the examination of predetermined high-interest regions of the sample as opposed to conventional bulk analytical techniques are valuable. Laser Desorption Synchrotron Postionization (synchrotron-LDPI) mass spectrometry is introduced as a novel analytical tool to characterize the molecular properties of organic compounds in mineral-organic samples from terrestrial systems, and it is demonstrated that when combined with Secondary Ion Mass Spectrometry (SIMS), can provide complementary information on mineral composition.Mass spectrometry along a decomposition gradient in density fractions, verifies the consistency of our results with bulk analytical techniques. We further demonstrate that by changing laser and photoionization energies, variations in molecular stability of organic compounds associated with mineral surfaces can be determined. The combination of synchrotron-LDPI and SIMS shows that the energetic conditions involved in desorption and ionization of organic matter may be a greater determinant of mass spectral signatures than the inherent molecular structure of the organic compounds investigated. The latter has implications for molecular models of natural organic matter that are based on mass spectrometric information.

Long-term litter decomposition controlled by manganese redox cycling

“…2C). To confirm that these mass fragments (i.e., m/z = 340, 370, 396, 399, 400, 406, and 414) correspond to aromatic structures, we determined ionization energies (IEs) for each of the fragments in a second LDPI experiment as previously described (31,32) and detailed in SI Materials and Methods. This method exploits the fact that aromatic ring structures have lower ionization energies (≤8.5 eV) than other organic moieties (>9 eV) (29,30).…”

“…To identify molecular changes in aromatic components of the litter (lignins and tannins), synchrotron-based laser desorption post ionization (LDPI) mass spectrometry of fresh needles and litter layers was performed on a modified time-of-flight secondary ion mass spectrometer (TOF.SIMS V; IonTOF) coupled to a synchrotron UV light port at beamline 9.0.2 of the Advanced Light Source (ALS) (29,31). To identify peaks in the resulting mass spectra that corresponded to aromatic structures, ionization energies for each of the most prominent mass peaks were determined as described in ref.…”

“…To identify peaks in the resulting mass spectra that corresponded to aromatic structures, ionization energies for each of the most prominent mass peaks were determined as described in ref. 31 and detailed in SI Materials and Methods. Based on the low IEs of larger aromatic systems (29,30), peaks with IEs of less than 8.5 eV were attributed to aromatic moieties.…”

Interaction of Natural Organic Matter with Layered Minerals: Recent Developments in Computational Methods at the Nanoscale

“…For example, synchrotron-based mass spectrometry allows the simultaneous collection of molecular level data on organic species, and information on the mineral structure on which they are adsorbed [158]. Neutron diffraction of layered minerals intercalated with polymers is another promising experimental approach to obtain interfacial structure [159].…”

Differential capacity of kaolinite and birnessite to protect surface associated proteins against thermal degradation

“…The fragments desorbed by the laser were then ionized with vacuum ultraviolet radiation (VUV) at a constant energy of 10.5 eV (Liu et al, 2013). The ions were then detected with the mass spectrometer with a detection limit of 3000 mass per charge (m/z).…”