Reflux open-vessel digestion system can overcome volatilization loss in mercury speciation analysis

Volatilization loss of analytes in open-vessel digestion is a concern for mercury speciation analysis. Loss of Hg⁰ vapour can be overcome by using oxidative digestion media, while loss of aerosols can be circumvented by complete condensation under sub-boiling-point heating. Using a simple system that consisted of a block heater and culture tubes, two digestion protocols were developed for determination of total Hg (tHg) and inorganic Hg (iHg). The resulting Hg⁺⁺ was selectively reduced by SnCl₂ to Hg⁰, which was detected by atomic fluorescence spectrometry (AFS). MeHg⁺ was oxidized to Hg⁺⁺ to yield tHg and calculated from the difference. These methods were validated using certified reference material (CRM) DORM-4, and applied to seafood analysis with 3.6 and 3.2 ng g^-1 (dry weight) limit of detection for iHg and tHg, respectively. Using only off-the-shelf components, these methods gained cost, simplicity, and parallel operation advantages.