The chemical speciation and bioavailability of mercury (Hg) is markedly influenced by its complexation with naturally dissolved organic matter (DOM) in aquatic environments. To date, however, analytical methodologies capable of identifying such complexes are scarce. We utilize ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) coupled with electrospray ionization to identify individual Hg-DOM complexes. The measurements were performed by direct infusion of DOM in 1:1 methanol:water solution at a Hg to dissolved organic carbon (DOC) molar ratio of 3×10-4. Heteroatomic molecules, especially those containing multiple S and N atoms, were found to be among the most important in forming strong complexes with Hg. Major Hg-DOM complexes of C10H21N2S4Hg+ and C8H17N2S4Hg+ were identified based on both the exact molecular mass and patterns of Hg stable isotope distributions detected by FTICR-MS in the Hg-DOM sample. Density functional theory was used to predict the solution-phase structures of candidate molecules and their chemical speciation. These findings represent the first step in unambiguously identifying specific DOM molecules in Hg binding, although future studies are warranted to further optimize the methodology and to explore detailed molecular compositions and structures of Hg-DOM complexes to fully understand the fate and bioavailability of Hg in the environment.

Identification of mercury and dissolved organic matter complexes using ultra-high resolution mass spectrometry

254th National Meeting (2017)

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