Direct humeome extraction from two german soils and molecular characterization by Electrospray-Orbitrap-Mass Spectrometry (ESI-Orbitrap-MS)

A silty and a sandy soil from Germany underwent the stepwise Humeomics fractionation. The humeome fractions obtained were analysed by High Performance Size Exclusion Chromatography hyphenated to Electrospray- Orbitrap Mass Spectrometry (MS). Empirical formulae were obtained by high resolution mass data and used to build Van Krevelen plots and describe the soil organic matter (SOM) of both soils. Results showed more than 200 masses for each soil distributed among fractions, some of which were present across more fractions and both soils. Compounds were classified according to molecular weight, unsaturation degree, oxygenation, and presence of nitrogen in the formula. Formulae with a single nitrogen atom, low insaturation and high oxygenation in their formulae were specific to the silty soil, while highly unsaturated CxHyOz compounds were exclusively found in the sandy soil. Nitrogenated compounds with high insaturation and low oxygenation rates were more numerous in the sandy soil. Semi quantitative assessment also differentiates the compounds, which are more abundant in aqueous extracts in the silty soil and in the residual fraction of the sandy soil. The direct analysis of SOM by MS profiling of these two soils shows the potential of Humeomics to provide a detailed molecular differentiation of soils.