Dissolved Organic Matter

Abstract

Dissolved organic matter (DOM) is a complex mixture of organic compounds that is ubiquitous in terrestrial, aquatic, and atmospheric environments. Although it plays a key role in the global carbon cycle, it remains poorly characterized at the molecular-level because of its compositional heterogeneity and variability. However, the use of NMR spectroscopy in DOM research has improved our understanding of the structure and reactivity of this important environmental matrix. Solid-state NMR provides an overview of the entire composition of isolated DOM samples, and is useful for examining changes in the structure of DOM from different locations or monitoring environmental processes such as sorption to soil minerals or land use changes. Compared with solid-state NMR experiments, solution-state NMR is capable of analyzing samples in their natural state and offers greater structural information about individual DOM components. In addition, a suite of one- and two-dimensional solution-state NMR experiments are available, which can be used to examine DOM functional group chemistry in greater detail. Coupling solution-state NMR techniques with sample cleanup or chromatographic separation steps can vastly improve the spectral resolution of DOM and permit the identification of a greater number of individual molecules. Furthermore, NMR is often used in conjunction with other advanced analytical techniques and provides complementary information that assists in the structural characterization of DOM. Keywords: dissolved organic matter; solid-state NMR; solution-state NMR; dissolved organic nitrogen; sorptive fractionation; organo-mineral interactions; hyphenated NMR