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Analytical and Bioanalytical Chemistry (v.358, #3)
“Mercury as a Global Pollutant”— International conference
by Rolf-Dieter Wilken; Milena Horvat (pp. 361-362).
Determination of artifactual formation of monomethylmercury (CH3Hg+) in environmental samples using stable Hg2+ isotopes with ICP-MS detection: Calculation of contents applying species specific isotope addition by H. Hintelmann; R. Falter; G. Ilgen; R. D. Evans (pp. 363-370).
Various extraction techniques, as distillation, acid and alkaline extraction, have been tested with regard to their potential to form a monomethylmercury (CH3Hg+) artifact from inorganic Hg during sample preparation. Hg2+ has been added to different reference materials in the form of enriched stable tracers and the formation of new methylmercury from that tracer has been analyzed by HPLC/ICP-MS and GC/ICP-MS. Both techniques gave comparable results. In particular, the distillation technique was prone to artifact formation. The resulting overestimation of methylmercury in sediments was as high as 80%. Artifact formation in hair, liver and algae samples was less significant, though still observable. Fish muscle tissue showed no artifact formation upon distillation, but some of the inorganic tracer was converted to methylmercury during alkaline extraction. Acid extraction of sediments resulted in low artifact formation rates. Fractionated measurements of sediment distillates revealed high methylmercury formation rates towards the end of the distillation process when acid concentrations in the solution are highest. A technique for correction of the measured apparent methylmercury content applying species specific isotope addition (SSIA) is proposed and the calculation scheme is presented.
Artifact formation of methyl mercury during aqueous distillation and alternative techniques for the extraction of methyl mercury from environmental samples by N. S. Bloom; John A. Colman; Lee Barber (pp. 371-377).
Aqueous distillation as a pre-extraction step for monomethyl mercury (MMHg) in waters and sediments is the most common method because it eliminates negative interferences in the aqueous ethylation procedure. However, the distillation procedure generates a positive MMHg artifact as a result of the action of naturally occurring organic substances on inorganic Hg in the sample. Methylation of Hg(II) does not occur in deionized water samples, indicating that the artifact is not due to the distillation itself or the reagents added (ammonium pyrrolidine dithiocarbamate, HCl), but rather to naturally occurring organic matter. Methylation of Hg(II) spikes ranged from 0.001% for rainwater and oligotrophic lake water to 0.08% for brown, humic-rich water. Methylation of Hg(II) spikes in sediments ranged from 0.005 to 0.1%, with the highest conversions in wetland peat. In most water samples, the artifact is not significant, as the ambient concentration of MMHg is 1–10% of the total, well above the contribution due to the artifact. The artifact may be significant in sediments and in Hg-contaminated water samples, where the measured fraction of MMHg is less than 1% of the total. The best of six alternative techniques involves leaching with KBr/H2SO4/CuSO4 and extraction into CH2Cl2, followed by back extraction into water, and subsequent ethylation.
Application of stable isotopes in environmental tracer studies – Measurement of monomethylmercury (CH3Hg+) by isotope dilution ICP-MS and detection of species transformation by H. Hintelmann; R. D. Evans (pp. 378-385).
The monovalent cation monomethylmercury (CH3Hg+) was determined in certified reference materials by isotope dilution GC/ICP-MS and good agreement between measured and certified values has been found. The use of enriched stable isotopes with subsequent detection by ICP-MS is a powerful tracer technique to study dynamic environmental processes. For the first time, it was possible to monitor opposite processes like Hg2+ methylation and CH3Hg+ demethylation at ambient tracer levels simultaneously in the same sample. A scheme for calculating the formation of new species from stable tracers used in environmental studies is presented. The sensitivity of stable tracer methods is superior to traditional tracer or radiotracer techniques. In case of mercury methylation, where the generation of a new compound is monitored, the limit of detection depends only on the precision of the isotope ratio measurements and the concentration of the ambient CH3Hg+ already present in the sample, not on the absolute detection limit of the GC/ICP-MS technique used for analyzing CH3Hg+. A 0.25% change in concentration of CH3Hg+ is detectable. In the case of CH3Hg+ demethylation, where the decrease of the added tracer is monitored, the detection limit again depends on the precision of the isotope ratio measurement and the ambient CH3Hg+ concentration but additionally on the amount of the added tracer as well. A decrease in the CH3Hg+ level of 2% of the added tracer is detectable. The validity of the calculation scheme was tested and no difference was found between individually measured isotope concentrations and calculated concentrations from solutions with multiple stable tracers.
Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder by Z. Xiao; J. Sommar; S. Wei; O. Lindqvist (pp. 386-391).
KCl coated denuders were employed for the measurement of divalent mercury (Hg2+) species in the air. Laboratory tests show that gaseous Hg2+ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg2+ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl2 reduction-CVAFS determination. Hg2+ concentrations of 0.04–0.15 ng m–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations.
Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades by M. L. Olson; L. B. Cleckner; J. P. Hurley; D. P. Krabbenhoft; T. W. Heelan (pp. 392-398).
Aqueous samples from the Florida Everglades present several problems for the analysis of total mercury (HgT) and methyl mercury (MeHg). Constituents such as dissolved organic carbon (DOC) and sulfide at selected sites present particular challenges due to interferences with standard analytical techniques. This is manifested by 1) the inability to discern when bromine monochloride (BrCl) addition is sufficient for sample oxidation for HgT analysis; and 2) incomplete spike recoveries using the distillation/ethylation technique for MeHg analysis. Here, we suggest ultra-violet (UV) oxidation prior to addition of BrCl to ensure total oxidation of DOC prior to HgT analysis and copper sulfate (CuSO4) addition to aid in distillation in the presence of sulfide for MeHg analysis. Despite high chloride (Cl-) levels, we observed no effects on MeHg distillation/ethylation analyses.
Mercury speciation methods for utility flue gas by D. Laudal; B. Nott; T. Brown; R. Roberson (pp. 397-400).
Accurate measurement of mercury speciation (Hg0 and Hg2+) in power plant flue gas is necessary to model the fate and transport of mercury in the atmosphere and understand and evaluate the effectiveness of mercury control technologies. Research work jointly sponsored by the Electric Power Research Institute (EPRI) and the U.S. Department of Energy (DOE) is currently under way at the University of North Dakota Energy & Environmental Research Center to determine whether U.S. Environmental Protection Agency (EPA) Method 29 or other methods can speciate mercury. Five different methods have been tested, and it has been found that EPA Method 29 does not speciate mercury properly in coal-generated flue gas. Two methods that show promise are the tris-buffer and the Ontario Hydro methods.
Determination of trace amounts of methylmercury in sediment and biological tissue by using water vapor distillation in combination with RP C18 preconcentration and HPLC-HPF/HHPN-ICP-MS by R. Falter; G. Ilgen (pp. 401-406).
A novel technique has been developed for the determination of trace amounts of methylmercury in sediment and biological tissues. The well known water vapor distillation technique for the isolation of methylmercury from different matrices was coupled with an RP C18 preconcentration using dithiocarbamate complexation. A newly developed HPLC-method allowed the separation of five different mercury species at different mercury masses with HPF/HHPN (High-Performance-Flow/Hydraulic-High-Pressure-Nebulizing) and detection by ICP-MS. The method takes advantage of the ability to measure individual isotopes. Recoveries of the water vapor distillation procedure samples for different mercury compounds from sediment were tested. For methylmercury, the detection limit for a 0.5 g sample was calculated to be 0.025 μg/kg. The new technique was assured using different reference materials.
Coupling of the RP C18 preconcentration HPLC-UV-PCO-system with atomic fluorescence detection for the determination of methylmercury in sediment and biological tissue by R. Falter; G. Ilgen (pp. 407-410).
An HPLC-UV-PCO-system (High Performance Liquid Chromatography, Ultraviolet, Post-Column Oxidation) was coupled with a cold vapor atomic fluorescence spectrometer (CVAFS) for separation and determination of mersalyl acid, methyl-, ethyl-, phenyl- and inorganic mercury. The mercury compounds were preseparated from the matrix using water vapor distillation. The compounds in the distillate were enriched as pyrrolidinedithiocarbamate complexes on an RP C18 preconcentration column and measured with the newly developed CVAFS detection system. The detection limit for methylmercury was 8 pg absolute for the enrichment of 5 mL distillate. The sensitivity of the HPLC-UV-PCO-CVAFS was improved by a factor of ten in comparison to a previously developed coupling technique with a cold vapor atomic absorption spectrometer (CVAAS). For methylmercury determination the detection limit for a 0.5 g sample was calculated to be 0.015 μg/kg.
Certification of total mercury and methylmercury concentrations in mussel homogenate (Mytilus edulis) reference material, IAEA-142 by M. Horvat; L. Liang; S. Azemard; V. Mandić; J.-P. Villeneuve; M. Coquery (pp. 411-418).
Due to the increased demand for new reference materials certified for total and methylmercury (MeHg) a sample of mussel homogenate (IAEA-142) has been prepared. Thirteen experienced laboratories reported results for total Hg of which 9 laboratories also reported results for MeHg content. Laboratories reporting MeHg results used various isolation techniques (solvent extraction, saponification, acid leaching, ion-exchange separation, and distillation) and detection systems (cold vapour atomic absorption spectrometry (CV AAS), cold vapour atomic fluorescence spectrometry (CV AFS), gas chromatography with electron capture detector (GC/ECD) and HPLC with CV AAS detector). In the case of total Hg, most of the laboratories used acid digestion, only two used alkaline dissolution, followed either by CV AAS or CV AFS. One laboratory used neutron activation analyses with radiochemical separation. The data received were in good agreement. The value for total Hg was certified to be 126 ng/g, with a 95% confidence interval from 119 to 132 ng/g. For MeHg the certified value of 47 ng/g expressed as Hg was assigned, with a 95% confidence interval from 43 to 51 ng/g. Stability testing has shown that both total and MeHg are stable if samples are stored in a dry and dark place at room temperature. The sample is now available as a certified reference material and is, in particular, useful for quality control measurements of Hg and MeHg in mussel samples at low concentration levels.
Overview of SM & T (BCR) activities for the quality control of mercury determination in the environment by P. Quevauviller (pp. 419-423).
The aim of the Standards, Measurements and Testing Programme (SM & T) of the European Commission (continuation of the BCR and Measurements and Testing Programmes) is to contribute to the harmonisation and improvement of methods and measurements carried out within the European Union and hence to the comparability of data necessary for e.g. trade activities, monitoring of environment, food and health, etc. R & D projects along these lines are currently funded; in the field of environmental analysis, they consist in most cases in the organisation of interlaboratory studies (intercomparisons and certifications of reference materials) in which laboratories may collaborate to improve the measurement or analysis concerned. Other activities are related to development of new methods and pre-normative research. This paper describes the objectives of the SM & T programme and the main actions undertaken, and gives examples of projects dealing with mercury determination in environmental matrices.
Certification of three mussel tissue standard reference materials (SRM) for methylmercury and total mercury content by M. K. Donais; Rajananda Saraswati; Elizabeth Mackey; Rabia Demiralp; Barbara Porter; Mark Vangel; Mark Levenson; Vesna Mandic; Sabine Azemard; Milena Horvat; Karl May; Hendrik Emons; Stephen Wise (pp. 424-430).
SRM 1974a, Organics in Mussel Tissue (Mytilus edulis); SRM 2974, Organics in Mussel Tissue (freeze-dried); and SRM 2976, Mussel Tissue (trace elements and methylmercury) have been recently certified for methylmercury and total mercury content. Three independent analytical procedures were used to determine the certified methylmercury concentrations. Four independent procedures combined with data from two intercomparison exercises were used to determine the certified total mercury concentrations. These materials are the first certified metal speciation environmental SRMs issued by the National Institute of Standards and Technology.
Certification of a Frozen Mussel Tissue Standard Reference Material (SRM 1974a) for Trace Organic Constituents by M. M. Schantz; Rabia Demiralp; Robert R. Greenberg; M. J. Hays; Reenie M. Parris; Barbara J. Porter; Dianne L. Poster; Lane C. Sander; Katherine S. Sharpless; Stephen A. Wise; Susannah B. Schiller (pp. 431-440).
NIST SRM 1974a, Organics in Mussel Tissue (Mytilus edulis), has been issued as a frozen tissue homogenate with certified mass fractions for 15 polycyclic aromatic hydrocarbons (PAHs), 20 polychlorinated biphenyl (PCB) congeners, and 7 chlorinated pesticides. Noncertified mass fractions are provided for an additional 18 PAHs, 4 PCB congeners, 4 chlorinated pesticides, 28 inorganic constituents, 16 aliphatic hydrocarbons, and methylmercury. The mass fractions for the measured PAHs range from approximately 1 μg/kg to 164 μg/kg dry mass while the mass fractions for the measured PCB congeners range from approximately 3 μg/kg to 150 μg/kg dry mass.
TUNA FISH (T-30) – A new proficiency testing material for the determination of As and Hg in seafood by B. Gawlik; Martine Druges; Michele Bianchi; Angelo Bortoli; Antonius Kettrup; Herbert Muntau (pp. 441-445).
The quality of the aquatic and marine environment can be monitored by the determination of pollutants in organisms living in this environment. Certified reference materials and well-organised proficiency tests are powerful means of ensuring a constant level of quality and verifying the correct application of standardised methods. The preparation of a tuna fish proficiency testing material for the evaluation of quality of As and Hg monitoring in seafood is described. Preparation and characterisation of the material as well as studies on its homogeneity and stability are described. Concentrations of 3.4 ± 0.2 mg/kg total arsenic and 2.91 ± 0.09 mg/kg total mercury have been determined as target values. Moreover indicative values for some trace elements (Cd, Cu, Ni, Pb, Sr) and some major constituents (Al, Br, C, Ca, Cl, Fe, H, K, Mg, N, Na, P, S, Si, Zn) have also been measured.
Quantification of mercury in soils and sediments – acid digestion versus pyrolysis by H. Biester; G. Nehrke (pp. 446-452).
Mercury (Hg) pyrolysis techniques allow the differentation of Hg-binding forms in contaminated soils and sediments. However, data about reproducibility and accuracy of the results concerning quantification of single Hg-compounds and total Hg-concentrations are rare. Therefore the total mercury concentration of different contaminated soils and sediments determined by using a pyrolysis technique were compared to those obtained after aqua regia digestion and cold vapor atomic absorption spectroscopy Hg detection. Twenty replicates of four soil and two sediment samples containing different Hg-compounds were investigated by both methods. All samples were analyzed without any pretreatment. For most of the samples total Hg-concentrations determined by pyrolysis show lower values, and up to threefold higher relative standard deviation(s) (RSD) than those obtained after wet digestion. Soil samples containing specified Hg-compounds like metallic Hg (Hg0) or cinnabar (α-HgS) show by far higher RSD by means of both methods than samples containing only matrix-bound Hg-compounds. Single peak integration indicate that the distribution of Hg0 and cinnabar is usually heterogeneous resulting in RSD of up to 85%, whereas RSD of matrix-bound Hg-compounds were always distinctly lower. Besides the higher standard deviation the pyrolysis technique has been found to be reliable for screening contaminated soils and sediments due to the important additional information about occurring Hg-binding forms.