Oxidized sterols as a significant component of dissolved organic matter: evidence from 2D HPLC in combination with 2D and 3D NMR spectroscopy

The elucidation of molecular structures present in dissolved organic matter (DOM) has the potential to unlock many of the queries associated with organic precursors, diagenetic processes and reactivity of this highly complex material. Suwannee River DOM was extensively fractionated by two dimensional hydrophilic interaction chromatography (HILIC)/HILIC and fractions were analyzed via a suite of two and three-dimensional NMR experiments. HILIC provided more greatly resolved fractions with a second dimension and enabled extensive and in-depth NMR analyses. The composite NMR experiments provide strong evidence for highly oxidized sterols as major structural components present in one of the most simplified and subsequently resolved fractions. Further interpretation of data on other fractions across the polarity gradient likewise supports the presence of alicyclic structures present with considerable hydroxyl groups, carboxylic acids and methyl groups associated with quaternary carbon suggesting that further sterol- and hopanoid-type structures are potentially dominant throughout DOM.