Utilization of Synthetic Oxygen-Functionalized, Carboxylate-Rich Alicyclic Molecule Analogues in Liquid Chromatography and Tandem Mass Spectrometric Analysis of Dissolved Organic Matter

Dissolved organic matter (DOM) is one of the most complex chemical mixtures known, with its chemical composition long puzzling biogeochemists. Identifying the chemical structures within DOM is essential for unraveling its origins and environmental fate. However, DOM’s complexity has impeded structural elucidation, with accurate functional group compositions from recalcitrant DOM poorly represented in the synthetic and isolative literature. Consequently, hypothesized DOM compounds are derived from models that inadequately represent true structures. To address this, carboxylic acid-only CRAM analogues were previously synthesized but failed to replicate the extensive fragmentation observed in marine DOM during tandem mass spectrometry (MS2). Here, we prepared CRAM analogues with numerous oxygen-functionalities to enable more diverse fragmentation pathways. Liquid chromatography studies showed functional group composition better predicted LC polarity than O/C ratio, and that alcohols represented early-eluting DOM profiles, while ethers ketones and lactones better represented central isomers. MS2 studies revealed α-hydroxy ketones and 1,2-diols led to the greatest backbone fragmentation, but remained less extensive than that of DOM. Ether and ester functionalities were labile even at low fragmentation energy, suggesting that such groups are likely contributors to core marine DOM carbon backbones, and contribute to the extensive fragmentation observed in all MS2 experiments.