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Species-specific isotope dilution with permeation tubes for determination of gaseous mercury species
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2003 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 75, no 20, 5584-5591 p.Article in journal (Refereed) Published
Abstract [en]

Instrumentation and methodology for determination of the gaseous mercury species Hg0, (CH3)2Hg, and CH3Hg+ has been developed. The method is based on continuous addition of gaseous isotopically enriched Hg species (tracers) at the point of sample acquisition, in combination with reduced pressure sampling on Carbotrap adsorbent tubes. Permeation tubes are used for generation of the tracers. Collected species are thermally desorbed and purged through an aqueous sodium tetraethylborate solution for derivatization of CH3Hg+. The purged gas is dried with a Nafion membrane, and the Hg species are subsequently collected on a smaller Tenax TA adsorbent tube. Species are then thermally desorbed from the Tenax TA and introduced into a gas chromatograph connected to an inductively coupled plasma mass spectrometer for separation and detection. To be able to add tracers during field sampling, we developed a portable device, supplying the permeation tubes with a thermostated and mass flow-controlled air stream of 5.0 ± 0.1 C and 50.0 mL min-1, respectively. Typical permeation rates obtained during a period of more than 6 weeks were 12.93 ± 0.56, 0.42 ± 0.01, and 0.49 ± 0.03 (mean ± standard deviation) pg of Hg min-1 for a set of 199Hg0, (CH3)2198Hg, and CH3200Hg+ tubes, respectively. Methodological detection limits (3) were determined to 700 pg of Hg m-3 for Hg0 and 50 pg of Hg m-3 for (CH3)2Hg and CH3Hg+. The collection efficiencies for sampled volumes of 400 L of synthetic air on the Carbotrap tubes used in this study were 13 ± 2, 102 ± 2, and 99 ± 4% for Hg0, (CH3)2Hg, and CH3Hg+, respectively. Desorption efficiencies for the above species and tubes were 98 ± 2, 98 ± 1, and 90 ± 4%, respectively. Fractions (20-40%) of the added (CH3)2198Hg and CH3200Hg+ tracers were found to be transformed during the analytical processing of collected air samples. Determined concentrations in the research laboratory air, corrected for species transformations, were 3-53, 8-11, and 1-2 ng of Hg m-3 for Hg0, (CH3)2Hg, and CH3Hg+, respectively. Concentrations in the ambient air were determined to be 2.1-2.6 ng m-3 for Hg0 and below the detection limit for (CH3)2Hg and CH3Hg+.

Place, publisher, year, edition, pages
ACS publications , 2003. Vol. 75, no 20, 5584-5591 p.
URN: urn:nbn:se:umu:diva-10051DOI: doi:10.1021/ac034324sOAI: diva2:149722
Available from: 2008-06-11 Created: 2008-06-11 Last updated: 2010-11-19Bibliographically approved
In thesis
1. Instrumental and methodological developments for isotope dilution analysis of gaseous mercury species
Open this publication in new window or tab >>Instrumental and methodological developments for isotope dilution analysis of gaseous mercury species
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with instrumental and methodological developments for speciation analysis of gaseous mercury (Hg(g)), based on isotope dilution analysis (IDA). The studied species include Hg0, (CH3)2Hg, CH3HgX and HgX2 (where X symbolises a negatively charged counter ion in the form of a halide or hydroxyl ion). Gas chromatography hyphenated with inductively coupled plasma mass spectrometry (GC-ICPMS) was used for separation and detection of Hg(g) species. Permeation tubes were used for the generation of gaseous isotopically enriched Hg standards (tracers). These tracers were continuously added to the sample gas stream during sampling of Hg(g). A mobile prototype apparatus incorporating both the permeation source and a sampling unit for collection of Hg(g) was developed and used for this purpose. Hg(g) species were pre-concentrated on Tenax TA and / or Carbotrap solid adsorbents. Au-Pt was used for pre-concentration of total Hg(g), either as the primary medium, or as backup. Collected species were eluted from these media and introduced to the instrument by thermal desorption.

Various degrees of species transformations, as well as losses of analyte during pre-concentration and elution, were found to occur for both Tenax TA and Carbotrap. The performance characteristics of these media were shown to be species specific, as well as matrix dependent. The development of an on-line derivatisation procedure allowed for minimised species transformations, as well as reduced adsorption and memory effects of ionic Hg(g) species within the analytical system. In conclusion, IDA provides an important tool for identification, minimisation and correction of the above mentioned analytical problems. Furthermore, it offers significant advantages with respect to quality assurance, compared to conventional techniques, both when it comes to rational development of new methodology, as well as for continuous validation of existing procedures.

The developed methodology for speciation analysis of Hg(g) has been tested in various applications, including the determination of Hg(g) species concentrations in ambient air (both in and outdoor) and in the head space of sediment microcosms. Hg(g) species were formed in the sediments as a result of naturally occurring redox and methylation processes, after addition of an isotope enriched aqueous Hg(II) precursor. The methodology has also been used for assessing the risk of occupational exposure to Hg(g) species during remediation of a Hg contaminated soil and for studying Hg0(g) transport and Au-Pt pre-concentration characteristics in natural gases. Hg0 was used as the model species in the latter experiments, since it is believed to be the dominating form of Hg(g) in natural gas. The results indicate that the occurrence of H2S can cause temperature dependent adsorption and memory effects of Hg0(g) in the presence of stainless steel, thereby providing a plausible explanation to the variability of results for sour gases occasionally observed in the field. Hg0(g) has demonstrated overall high recovery during collection on Au-Pt tubes for all gases tested in this thesis. Recent (unpublished) results however indicate that there are potential species specific and matrix dependent effects associated with the Au-Pt based pre-concentration of Hg(g) in natural gases.

Place, publisher, year, edition, pages
Umeå: Kemi, 2007. 46 p.
Mercury, gas, species, speciation analysis, isotope dilution analysis, permeation tubes
National Category
Analytical Chemistry
urn:nbn:se:umu:diva-1448 (URN)978-91-7264-463-2 (ISBN)
Public defence
2007-12-15, Lilla hörsalen, KBC, 90187, Umeå, 13:00 (English)
Available from: 2007-11-22 Created: 2007-11-22 Last updated: 2010-11-19Bibliographically approved

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