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Instrumental and methodological developments for isotope dilution analysis of gaseous mercury species
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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.
Keyword [en]
Mercury, gas, species, speciation analysis, isotope dilution analysis, permeation tubes
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-1448ISBN: 978-91-7264-463-2 (print)OAI: oai:DiVA.org:umu-1448DiVA: diva2:141102
Public defence
2007-12-15, Lilla hörsalen, KBC, 90187, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2007-11-22 Created: 2007-11-22 Last updated: 2010-11-19Bibliographically approved
List of papers
1. Species-specific isotope dilution with permeation tubes for determination of gaseous mercury species
Open this publication in new window or tab >>Species-specific isotope dilution with permeation tubes for determination of gaseous mercury species
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
Identifiers
urn:nbn:se:umu:diva-10051 (URN)doi:10.1021/ac034324s (DOI)
Available from: 2008-06-11 Created: 2008-06-11 Last updated: 2017-12-14Bibliographically approved
2. Species specific isotope dilution with on line derivatisation for determination of gaseous mercury species
Open this publication in new window or tab >>Species specific isotope dilution with on line derivatisation for determination of gaseous mercury species
2005 (English)In: Journal of Analytical Atomic Spectrometry, ISSN 0267-9477, E-ISSN 1364-5544, Vol. 20, no 11, 1232-1239 p.Article in journal (Refereed) Published
Abstract [en]

A species specific isotope dilution (SSID) method for determination of the volatile mercury (Hg) species Hg0, (CH3)2Hg, CH3HgX and HgX2(where X is a counter ion) in gaseous samples was developed. The procedure involved on line derivatisation of ionic Hg species with sodium tetraethylborate during sampling, before collection of species on a Tenax TA tube in series with an Au–Pt tube. Collected species were thermally desorbed and determined by GC-ICP-MS. The procedure provided absolute detection limits of 0.5 pg for CH3HgX and (CH3)2Hg, 5 pg for HgX2 and 25 pg for Hg0. Recoveries and transformations of the investigated species were studied for the different procedural steps and the method was tested for microcosm experiments on brackish water sediment samples, as well as for laboratory air samples. As a result of methylation and reduction processes within the sediment, gaseous emission rates could be determined for all investigated species after addition of an isotope enriched aqueous inorganic 199Hg2+ standard to the sediment. Hg0 was the only specie detected in laboratory air samples (4.5 ng m–3). The procedure for derivatisation of ionic Hg species prior to collection on Tenax TA reduces memory effects and transformations of CH3HgX and HgX2, which is especially advantageous at low sample gas flow rates and for complex gaseous matrices, such as emissions from sediment samples. SSID provides simplified methodological development, as well as efficient correction for matrix induced losses and transformations of Hg species. The method could be useful for various biogeochemical studies of Hg, as well as for reliable risk assessments during, for example, waste management and soil remediation.

Place, publisher, year, edition, pages
RCS Publishing, 2005
Identifiers
urn:nbn:se:umu:diva-12910 (URN)doi:10.1039/b504678e (DOI)
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2017-12-14Bibliographically approved
3. Studies of transport and collection characteristics of gaseous mercury in natural gases using amalgamation and isotope dilution analysis
Open this publication in new window or tab >>Studies of transport and collection characteristics of gaseous mercury in natural gases using amalgamation and isotope dilution analysis
2007 (English)In: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 132, no 6, 579-586 p.Article in journal (Refereed) Published
Abstract [en]

Transport and collection characteristics were studied for gaseous elemental mercury (Hg0(g)) in natural gases using newly developed methodology based on amalgamation, isotope dilution with permeation tubes and inductively coupled plasma mass spectrometry. The study involved different Au–Pt collection tube designs, tubing materials and gaseous matrices, including air, natural and sales gas, as well as methane and sales gas to which hydrogen sulfide (H2S) had been added. The Hg0(g) capacity of the Au–Pt tubes was determined to 3.5 ± 0.1 µg. Blanks and detection limits of gaseous mercury (Hg(g)) were 58 ± 17 pg m–3 and 50 pg m–3, respectively, for a 60 L sample volume. For the gases tested, added Hg0(g) tracers could be collected with 90% or higher efficiency at flow rates and volumes of up to 10 L min–1 and 100 L, respectively. The collection efficiency was found to be independent of the type of gas tested, even in the presence of H2S. However, for the gases containing H2S, the apparent transport efficiency of added Hg0(g) tracers through stainless steel tubing varied from 50 to 150% upon changing the temperature from 25 to 100 °C. The interaction of stainless steel with Hg0(g) leading to either a sink, or source of Hg, was not observed in the absence of H2S, nor was it observed for PTFE tubing in the presence of H2S. These observations raise questions about the applicability of currently used sampling procedures for determination of Hg(g) in H2S rich natural gases, including the 6978-2 ISO standard method, in which stainless steel is a prescribed material for tubing and valves of the sampling apparatus.

Place, publisher, year, edition, pages
RSC Publishing, 2007
Identifiers
urn:nbn:se:umu:diva-14415 (URN)doi:10.1039/b702058a (DOI)
Available from: 2007-05-31 Created: 2007-05-31 Last updated: 2017-12-14Bibliographically approved
4. Recent Advances in Mercury Speciation Analysis with Focus on Spectrometric Methods and Enriched Stable Isotope Applications
Open this publication in new window or tab >>Recent Advances in Mercury Speciation Analysis with Focus on Spectrometric Methods and Enriched Stable Isotope Applications
Show others...
2007 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 36, no 6, 443–51- p.Article in journal (Refereed) Published
Abstract [en]

This paper discusses some recent advances in spectrometric methods and approaches for mercury speciation analysis of environmental samples with focus on isotope dilution techniques for determination of mercury species' concentrations in gaseous samples and reaction rates in soils and sediments. Such analytical data is important inter alia in fundamental research on mercury biogeochemistry and for risk assessments of mercury-contaminated soils and sediments and for designing effective remedial actions. The paper describes how the use of enriched stable isotope tracers in mercury speciation analysis can improve the traceability and accuracy of results, facilitate rational method developments, and be useful for studying biogeochemical processes, i.e. rate of reactions and fluxes, of mercury species. In particular the possibilities to study and correct for unwanted species transformation reactions during sample treatment and to study “natural” transformations of species in environmental samples, or micro- and mesocosm ecosystems, during incubations are highlighted. Important considerations to generate relevant data in isotope tracer experiments as well as reliability and quality assurance of mercury speciation analysis in general are also discussed.

Identifiers
urn:nbn:se:umu:diva-16888 (URN)doi:10.1579/0044-7447(2007)36[443:RAIMSA]2.0.CO;2 (DOI)
Available from: 2008-01-29 Created: 2008-01-29 Last updated: 2017-12-14Bibliographically approved

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