A novel method for stable isotope measurement of gaseous elemental mercury

<p>Here, we introduce a new methodology developed for highly precise stable mercury isotope ratio (&#948;Hg) analysis: the sampling method collecting sufficient amount of gaseous elemental mercury (GEM) from air within 24 h or less and the extraction method effectively converting the collected GEM to Hg²⁺ in less than 10 mL of acidified solution.</p><p>A big gold-amalgam trap (BAuT), which has approximately 11 times larger inner diameter of the tube and more gold-amalgam granular than a conventional gold-amalgam trap, was designed for quick and effective sampling of GEM in a short time period. A 24-h sampling demonstrated that the collection efficiency was higher than 99.9% under the flow rate of 55 LPM. Prior to the extraction the collected GEM by BAuT was pre-concentrated to a conventional gold-amalgam trap to reduce the dead volume.</p><p>The GEM pre-concentrated was transferred into a four side sealed 2L Tedler bag with a PTFE stopcock by heating the gold-amalgam trap to 600 &#186;C for ~ 4 min under the 0.5 LPM flow of Hg-free air. Prior to this transfer 5mL of 0.5~40% (v/v) reversed aqua resia or RAR (hydrochloric acid: nitric acid = 1:2) was pre-introduced into the bag. The bag with GEM and RAR was left for the conversion of GEM into the stable state in the solution (i.e., Hg²⁺). The solution recovered was then analyzed by multi collector-ICP-MS for the Hg concentration and &#948;Hg.</p><p>Results with a standard reference material showed that the recovery from the test with 10% RAR and the extraction duration of 8 days was the highest, 97%, with the 5% of recovery for the residual GEM in the gas-phase. The &#948;Hg analysis for five isotope ratios exhibited that the accuracy was between 0.01 and 0.3 &#8240;. Results from the analytical tests of ambient GEM using this methodology will be discussed.</p>