Feasibility of Metal Oxide Glasses and Polymer Membranes as Sorbents for Gaseous Oxidized Mercury

Mass spectrometry methods are currently under development by the atmospheric mercury (Hg) research community to elucidate the identity of atmospheric oxidized mercury (Hg^II) compounds. Due to high instrument detection limits, materials that can quantitatively preconcentrate atmospheric Hg^II without facilitating compound-altering chemical reactions are needed to support these methods. Cation exchange membranes (CEM) and nylon membranes are currently used to preconcentrate ambient Hg^II for concentration measurements and Hg^II compound estimation, respectively. However, CEM and nylon membranes are poor candidates for observations by mass spectrometry methods due to release of interfering compounds upon heating; glasses do not have this problem. Here, three metal oxide glasses were explored as potential alternatives for Hg^II preconcentration for future use with mass spectrometry methods: calcium phosphate (CaP), iron phosphate (FeP), and calcium aluminate (CaAl). The glasses demonstrated quantitative selective capture of HgBr₂ without capture of Hg⁰. Under ambient conditions, the CaP, FeP, and CaAl sorbed 36.4 ± 12.6% of the total Hg^II as the CEM. However, when Hg concentrations were normalized to surface area, CaP, FeP, and CaAl sorbed more HgBr₂ in the laboratory and ambient Hg^II compared to CEM. The CEM and CaP retained similar concentrations of HgBr₂ when preloaded samples were deployed in the field. Additionally, a permeation tube-based calibrator was used to load sorbents with HgBr₂ for investigation of Hg^II retention on CEM and thermal desorption profile changes on nylon membranes during active sampling. Nylon membranes were purchased from three vendors and used to compare HgBr₂ retention; a different HgBr₂ thermal desorption profile was achieved for each vendor’s nylon membrane.