Characterisation of dissolved organic matter using Fourier-transform ion cyclotron resonance mass spectrometry: Type-specific unique signatures and implications for reactivity.

This study investigated the chemodiversity and unique signatures for dissolved organic matter (DOM) from different types of water using high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Eight freshwater hydrophobic DOM (HPO) share 10-17% formulas that were mainly lignin-like compounds. Unique signatures were synthesized: unique to the high-humic HPO (Suwannee River and Blavet River) were condensed aromatic and some aliphatic compounds with H/C > 1.5 and O/C < 0.2, which is considered as decisive of these black river water. Medium-humic isolates (Loire River, Seine River, South Platte River, and Ribou Dam) did not show explicit unique signatures. Nonetheless, enhanced chemodiversity was observed for medium-humic isolates extracted from a variety of indigenous environmental conditions. As an example, South Platte River HPO isolated in winter showed signatures similar to low-humic HPO (Colorado River), i.e., predominantly aliphatic CHO (H/C > 1.0). Effluent HPO was mainly aliphatic molecules with 0.2 < O/C < 0.5 and enriched in S-bearing molecules, and molecules unique to glacial DOM (Pony Lake) incorporated N-bearing compounds that were inferiorly oxidized and were considered as microbial-derived. The weight-averaged double bond equivalent and elemental ratio derived from FTICR-MS were compared with SUVA and the results from elemental analysis. This acts as the first study to synthesize unique chemical compositions that distinguish different types of DOM and determine certain reactivity. It is also a significant reference for future studies using similar types of DOM.