ac7b04555_si_001.pdf (1.51 MB)
Hg Compound-Specific Isotope Analysis at Ultratrace Levels Using an on Line Gas Chromatographic Preconcentration and Separation Strategy Coupled to Multicollector-Inductively Coupled Plasma Mass Spectrometry
journal contribution
posted on 2018-06-07, 00:00 authored by Sylvain Bouchet, Sylvain Bérail, David AmourouxStable Hg isotope analyses are nowadays
widely employed to discriminate Hg sources and understand its biogeochemical
cycle. Until now, total Hg isotopic compositions have been mainly
used but Hg compound-specific isotopic analysis (CSIA) methodologies
are emerging. Online Hg-CSIA were limited to samples containing high
concentrations, but in this work we overcome this limitation for the
measurement of inorganic (IHg) and monomethylmercury (MMHg) by gas
chromatography hyphenated to multicollector-inductively coupled plasma
mass spectrometry (GC/MC-ICPMS) through the use of an automated
online preconcentration strategy, allowing injection volumes up to
100 times larger than usual. The preconcentration of Hg species and
subsequent transfer to the column were achieved by a programmed temperature
vaporization (PTV) injector fitted with a packed liner. The PTV parameters
were first optimized using a quadrupole ICPMS, and then its suitability
for Hg-CSIA was evaluated with long-term replicate analysis of various
standards and reference materials (RMs). The large preconcentration
capability enables analyses with Hg concentrations in the organic
solvent 2 orders of magnitude lower than the previous conventional
GC/MC-ICPMS method, but a compound specific standard bracketing procedure
was required for MMHg in order to correct for the differential behavior
of Hg species in the liner. The external reproducibility of the method
ranged from 0.19 to 0.39 ‰ for Δ199Hg and
δ202Hg (as 2 SD, n = 143–167)
depending on the species. The analysis of various RMs demonstrated
the applicability to environmental samples with species concentrations
down to about 150 ng g–1. This new methodology opens
the way for a much wider range of online Hg-CSIA measurements that
will improve our understanding of the Hg biogeochemical cycle.