There is increasing interest regarding potential impacts of soil organic matter (SOM) in the environment, such as acting as contaminant complexants, influencing microbial community structure, function, and stability, and as a vulnerable source of CO<sub>2</sub> and its feedback to global warming. Current methods used to characterize SOM lack molecular and elemental detail necessary to develop mechanistic understanding of key processes that operate in the belowground ecosystem. As a result current biogeochemical models of terrestrial carbon cycle do not adequately represent these important belowground processes and result in predictions of future climatic conditions with large uncertainty. This highlights the need to understand processes by which carbon is cycled through terrestrial ecosystems at a molecular level. In this study, we present a super critical fluid extraction (SCFE) method and assign molecular formulas to thousands of organic molecules that constitute SOM. Online SCFE methods were developed to deliver highly concentrated products directly onto chromatography columns allowing for easy coupling of the extraction product to a liquid chromatography (LC) system and subsequently mass spectrometry analysis. EMSL’s extensive expertise and capabilities in ultrahigh resolution mass spectrometry (UHR MS) enabled the examination of molecules, directly from the on-column extract, with ultrahigh mass resolution and sub-ppm mass accuracy. Extracts and spent soil sample were solvent free, creating a robust/powerful alternative approach to solvent-based methods for the extraction of SOM from soil. The LCMS technique identified thousands of organic molecules present in SOM and characterized the chemical diversity of organic molecules present in soil. This on-column SCFE system was compared to a commercially available SCFE system to determine the advantages of collecting extracts directly on column and sensitivity of the systems with varying sample sizes. The use of a Van Krevelen diagram of the LCMS SOM extract data made it possible to visualize the diversity of chemical compounds that were extracted from the soil using the two techniques. Lipids, proteins, carbohydrates, lignins and tannins have all been identified.

Characterization of soil organic matter (SOM) using online supercritical fluid extraction (SCFE) techniques coupled with liquid chromatography-ultrahigh resolution mass spectrometry (LC-UHR MS)

249th National Meeting (2015)

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