Soil Organic Matter Characterization by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR MS): A Critical Review of Sample Preparation, Analysis, and Data Interpretation

Abstract

The biogeochemical cycling of soil organic matter (SOM) plays a central role in regulating soil health, water quality, carbon storage, and greenhouse gas emissions. Thus, many studies have been conducted to reveal how anthropogenic and climate variables affect carbon sequestration and nutrient cycling. Among the analytical techniques used to better understand the speciation and transformation of SOM, Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) is the only technique that has sufficient mass resolving power to separate and accurately assign elemental compositions to individual SOM molecules. The global increase in the application of FTICR MS to address SOM complexity has highlighted the many challenges and opportunities associated with SOM sample preparation, FTICR MS analysis, and mass spectral interpretation. Here, we provide a critical review of recent strategies for SOM characterization by FTICR MS with emphasis on SOM sample collection, preparation, analysis, and data interpretation. Data processing and visualization methods are presented with suggested workflows that detail the considerations needed for the application of molecular information derived from FTICR MS. Finally, we highlight current research gaps, biases, and future directions needed to improve our understanding of organic matter chemistry and cycling within terrestrial ecosystems.

The Sources, Molecular Compositions, and Light Absorption Properties of Water‐Soluble Organic Carbon in Marine Aerosols From South China Sea to the Eastern Indian Ocean

“…The number of identified formulas in Marine-influenced regions was comparable to that in remote North Atlantic Ocean regions (Gurganus et al, 2015;Wozniak et al, 2014), but lower than those in SEA-influenced and SA-influenced regions, suggesting that the complexity of sources and atmospheric processes in marine aerosols was lower for remote marine regions. In addition, the lower identified formulas for Marine-influenced regions may also reflect that the primary marine organic compounds do not ionize well in the ESI mode (Bianco et al, 2018;Wozniak et al, 2014) ( Bahureksa et al, 2021;Koch & Dittmar, 2006). In this study, we found that both AI mod,w and DBE/C w were higher in SEA-influenced and SA-influenced regions, suggesting compared to Marine-influenced regions, the Continental-influenced regions were characterized by relatively high aromaticity.…”

“…The intensity‐weight O/C (O/C w ) and DBE (DBE w ) were lower in Marine‐influenced regions than in SEA‐influenced and SA‐influenced regions (Table S2 in Supporting Information ), indicating a relatively lower oxidation and unsaturation level for Marine‐influenced regions. AI mod and DBE/C are two indicators widely used to represent the aromaticity of organic matter in natural environments (Bahureksa et al., 2021; Koch & Dittmar, 2006). In this study, we found that both AI mod, w and DBE/C w were higher in SEA‐influenced and SA‐influenced regions, suggesting compared to Marine‐influenced regions, the Continental‐influenced regions were characterized by relatively high aromaticity.…”

Organic Matter Transformations are Disconnected Between Surface Water and the Hyporheic Zone

“…All these factors have been studied to some degree in river corridors, and advances in cheminformatics techniques can provide further insights specifically into the biotic and abiotic components of OM transformations. More specifically, Fudyma et al (2021) used the ultra-high mass resolution of Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) data (Marshall et al, 1998;Bahureksa et al, 2021) to infer putative abiotic and abiotic transformations of OM in a river corridor system. This extended previously-developed cheminformatics techniques (e.g., Breitling et al, 2006;Danczak et al, 2020Danczak et al, , 2021 to include abiotic transformations.…”

Mass difference matching unfolds hidden molecular structures of dissolved organic matter

“…Complex mixtures are key study objects in environmental and industrial applications, but their analysis remains challenging. [1][2][3][4] One of the most complex mixtures in natural ecosystems is dissolved organic matter (DOM). 5,6 DOM is a central intermediate of ecosystem metabolism and mirrors molecular imprints of interactions with its abiotic and biotic environment [7][8][9] , which form the basis for processes such as carbon sequestration and nutrient recycling.…”

“…5,6 DOM is a central intermediate of ecosystem metabolism and mirrors molecular imprints of interactions with its abiotic and biotic environment [7][8][9] , which form the basis for processes such as carbon sequestration and nutrient recycling. 10,11 Despite significant advances in ultrahigh-resolution mass spectrometry (FTMS) 2,4 and nuclear magnetic resonance spectroscopy 12 , scientists still struggle to decode this information on the molecular level [13][14][15][16][17] , and novel approaches to identify distinct structures are required to translate molecular-level information into improved process understanding.…”