Determination of Mercury Content in a Shallow Firn Core from Greenland by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

Abstract

The total mercury content was determined in 6 cm sections of a shallow 7 m firn core and in surrounding surface snow from Summit, Greenland (elevation: 3238 m, 72.58∘N, 38.53∘W) collected in May 2001 by isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS). The focus of this research was to evaluate the capability of the ID-CV-ICP-MS technique for measuring trace levels of Hg typical of polar snow and firn. Highly enriched 201Hg isotopic spike is added to approximately 10 mL melted core and thoroughly mixed. The Hg2+ in the sample is reduced on line with tin(II) chloride (SnCl2) and the elemental Hg (Hg∘) vapor pre-concentrated onto gold gauze using a commercial amalgam system. The Hg is then thermally desorbed and introduced into a quadrupole ICP-MS. The blank-corrected Hg concentrations determined for all samples ranged from 0.25 to 1.74 ng/L (ppt) (average 0.59 ± 0.28 ng/L (1σ)) and fall within the range of those previously determined by Boutron et al. [Geophys. Res. Lett. 25, 1998, 3315–3318] (≤ 0.05–2.0 ng/L) for the Summit site. The average blank value was 0.19 ± 0.045 ng/L (n = 6, 1σ) and the method detection limit was 0.14 ng/L. The Hg values specifically for the firn core range from 0.25 to 0.87 ng/L (average 0.51 ± 0.13 ng/L (1σ)) and show both values declining with time and larger variability in concentration in the top 1.8 m.