Isolation and Identification of Mercury-Dissolved Organic Matter Complexes in Mercury-Humic Acid Suspensions

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Aquatic Chemistry

Background:

• Mercury (Hg) complexation with dissolved organic matter (DOM) significantly impacts its fate in aquatic systems.
• Identifying these Hg-DOM complexes is challenging due to low concentrations and interfering ions.

Purpose of the Study:

• To develop and validate a method for isolating and identifying mercury-dissolved organic matter (Hg-DOM) complexes.
• To gain insights into mercury speciation, bioavailability, and transformations in aquatic environments.

Main Methods:

• Solid-phase extraction (SPE) was used to isolate Hg-DOM complexes from humic acid suspensions.
• Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) was employed for putative identification of Hg-DOM complexes.
• C18 SPE cartridges demonstrated higher efficiency in extracting Hg-DOM complexes compared to PPL cartridges at circumneutral pH.

Main Results:

• SPE coupled with FTICR-MS effectively isolated and identified Hg-DOM complexes.
• The C18 SPE method identified eight Hg-DOM complexes, outperforming PPL cartridges which identified two.
• A specific mercury-containing molecule (C8H13HgN2O2S) was consistently identified, indicating method robustness.

Conclusions:

• The developed SPE-FTICR-MS methodology is effective for characterizing Hg-DOM complexes.
• This approach enhances understanding of Hg speciation, bioavailability, and transport in aquatic ecosystems.
• The study provides a pathway to investigate Hg-DOM interactions at environmentally relevant concentrations.