182 Organic compounds in soils, sediments & sludges
was extracted into pesticide grade benzene containing approximately 100 µg1
−1 of
ethyl mercuric chloride as an internal standard. The extract was analysed by electron
capture gas chromatography. The detection limit was 1–2 µg kg
−1 .
Rodriguez Martin-Diomeadios et al [73] used speciated isotope dilution coupled with gas chromatography-undiluted coupled with plasma mass spectrometry to
determine and unravel the artificial formation of monomethyl mercury in reference
samples.
Sediment samples
Speciated-dilution mass spectrometry (SID-MS) is claimed to be an absolute method;
however, it has been found to be affected by artefact monomethylmercury formation
in sediments. The determination chloromethylmercury in sediments was carried out
by SID-MS after open-focused microwave extraction. The extracted mercury species
were then ethylated and separated by capillary gas chromatography. Isotope ratios
(peak area ratios at different masses) were measured by on-line ICP-MS detection
of the capillary gas chromatographically-separated compounds. Reproducibility of
202 Hg/
201 Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for
Et 2 Hg: for
202 Hg/
199 Hg, 0.43 and 0.46%, respectively, were determined. The absolute
detection limits for capillary gas chromatography-ICPMS measurements were better
than 26 fg for
202 Hg, 20 fg for
201 Hg, and 24 fg for
199 Hg. For the direct determination
of monomethylmercury in sediment reference materials (CRM 580, IAEA 356, and
IAEA 405), higher values than the certified were always found. Systematic experiments
were carried out to localise the sources of the unintentional abiotic methylmercury
formation during analysis. Different spiking and derivatisation procedures (either ethylation, propylation, or derivatisation by Grignard reagents) were tested. In addition,
isotopically enriched inorganic mercury was spiked. The amount of inorganic mercury initially present in the sample was found to be the critical factor that should be
known and carefully controlled. A simple solvent extraction technique involving no
critical steps was applied in order to reduce Hg
2+ concentration when it is high. The
method was applied to the determination of monomethylmercury in sediment reference material IAEA-405 with satisfactory results after organic solvent extraction. The
limitations of applicability of the proposed method are evaluated as related to inorganic mercury, organic carbon, and sulphur contents. The results obtained confirmed
that available sediment reference materials are adequate to achieve traceable mercury
speciation analysis and to detect potential sources of monomethylmercury artefact
formation.
Jensen and Jernelou et al [74] reported that both mono and dimethylmercury
(CH 3 Hg
+ and (CH 3 ) 2 Hg) can be produced in lake sediments and in fish. The gases
evolved from incubated sediment samples were analysed for monomethyl mercury by
conversion to methyl mercury halide by means of gas chromatography, using electron
capture and mass spectrometric detection.
Cappon and Crispin Smith et al [75] have described a method for the extraction,
clean-up and gas chromatographic determination of alkyl and aryl mercury compounds
in sediments. The organomercury compounds are converted to their chloro-derivatives
and solvent extracted. Inorganic mercury is then isolated as methylmercury upon
reaction with tetramethyltin. The initial extract is subjected to a thiosulphate clean-up
was extracted into pesticide grade benzene containing approximately 100 µg1
−1 of
ethyl mercuric chloride as an internal standard. The extract was analysed by electron
capture gas chromatography. The detection limit was 1–2 µg kg
−1 .
Rodriguez Martin-Diomeadios et al [73] used speciated isotope dilution coupled with gas chromatography-undiluted coupled with plasma mass spectrometry to
determine and unravel the artificial formation of monomethyl mercury in reference
samples.
Sediment samples
Speciated-dilution mass spectrometry (SID-MS) is claimed to be an absolute method;
however, it has been found to be affected by artefact monomethylmercury formation
in sediments. The determination chloromethylmercury in sediments was carried out
by SID-MS after open-focused microwave extraction. The extracted mercury species
were then ethylated and separated by capillary gas chromatography. Isotope ratios
(peak area ratios at different masses) were measured by on-line ICP-MS detection
of the capillary gas chromatographically-separated compounds. Reproducibility of
202 Hg/
201 Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for
Et 2 Hg: for
202 Hg/
199 Hg, 0.43 and 0.46%, respectively, were determined. The absolute
detection limits for capillary gas chromatography-ICPMS measurements were better
than 26 fg for
202 Hg, 20 fg for
201 Hg, and 24 fg for
199 Hg. For the direct determination
of monomethylmercury in sediment reference materials (CRM 580, IAEA 356, and
IAEA 405), higher values than the certified were always found. Systematic experiments
were carried out to localise the sources of the unintentional abiotic methylmercury
formation during analysis. Different spiking and derivatisation procedures (either ethylation, propylation, or derivatisation by Grignard reagents) were tested. In addition,
isotopically enriched inorganic mercury was spiked. The amount of inorganic mercury initially present in the sample was found to be the critical factor that should be
known and carefully controlled. A simple solvent extraction technique involving no
critical steps was applied in order to reduce Hg
2+ concentration when it is high. The
method was applied to the determination of monomethylmercury in sediment reference material IAEA-405 with satisfactory results after organic solvent extraction. The
limitations of applicability of the proposed method are evaluated as related to inorganic mercury, organic carbon, and sulphur contents. The results obtained confirmed
that available sediment reference materials are adequate to achieve traceable mercury
speciation analysis and to detect potential sources of monomethylmercury artefact
formation.
Jensen and Jernelou et al [74] reported that both mono and dimethylmercury
(CH 3 Hg
+ and (CH 3 ) 2 Hg) can be produced in lake sediments and in fish. The gases
evolved from incubated sediment samples were analysed for monomethyl mercury by
conversion to methyl mercury halide by means of gas chromatography, using electron
capture and mass spectrometric detection.
Cappon and Crispin Smith et al [75] have described a method for the extraction,
clean-up and gas chromatographic determination of alkyl and aryl mercury compounds
in sediments. The organomercury compounds are converted to their chloro-derivatives
and solvent extracted. Inorganic mercury is then isolated as methylmercury upon
reaction with tetramethyltin. The initial extract is subjected to a thiosulphate clean-up