Structural Analysis of Dissolved Organic Matter with Hydrophilic Interaction Liquid Chromatography and Nuclear Magnetic Resonance Spectroscopy

摘要

Comprised of thousands of unknown constituents, dissolved organic matter (DOM) is thought to be one of the most complex natural mixtures on Earth [1]. Of the many analytical techniques applied to the structural analyses of DOM, nuclear magnetic resonance (NMR) spectroscopy is amongst the most promising techniques for the structural characterization of unknown compounds. The severe signal overlap, however, generated from NMR detection of DOM inhibits our ability to access molecular-level information of this extremely heterogeneous substance. Separation into more homogenous fractions is a fitting solution to overlapping signals but chromatographic separations such as those afforded by high performance liquid chromatography (HPLC) have traditionally been poorly resolved when applied to DOM separations. The aim of the research presented here was to explore the potential of hydrophilic interaction liquid chromatography (HILIC) as a tool for simplifying DOM prior to NMR analyses. HILIC is an attractive option compared to many reverse phase HPLC techniques as it is ideal for separating more polar constituents such as might be found in the highly degraded and oxidized molecules of DOM. In addition to NMR analyses, HILIC-generated DOM fractions were analyzed with excitation-emission matrix (EEM) fluorescence spectroscopy as a means of correlating NMR-derived structural information with fluorescence characteristics.