Novel methodology for the study of mercury methylation and reduction in sediments and water using <Superscript>197</Superscript>Hg radiotracer

Mercury tracers are powerful tools that can be used to study mercury transformations in environmental systems, particularly mercury methylation, demethylation and reduction in sediments and water. However, mercury transformation studies using tracers can be subject to error, especially when used to assess methylation potential. The organic mercury extracted can be as low as 0.01% of the endogenous labeled mercury, and artefacts and contamination present during methylmercury (MeHg) extraction processes can cause interference. Solvent extraction methods based on the use of either KBr/H₂SO₄ or HCl were evaluated in freshwater sediments using ¹⁹⁷Hg radiotracer. Values obtained for the ¹⁹⁷Hg tracer in the organic phase were up to 25-fold higher when HCl was used, which is due to the coextraction of ¹⁹⁷Hg²⁺ into the organic phase during MeHg extraction. Evaluations of the production of MeHg gave similar results with both MeHg extraction procedures, but due to the higher Hg²⁺ contamination of the controls, the uncertainty in the determination was higher when HCl was used. The Hg²⁺ contamination of controls in the HCl extraction method showed a nonlinear correlation with the humic acid content of sediment pore water. Therefore, use of the KBr/H₂SO₄ method is recommended, since it is free from these interferences. ¹⁹⁷Hg radiotracer (T _1/2 = 2.673 d) has a production rate that is about 50 times higher than that of ²⁰³Hg (T _1/2 = 46.595 d), the most frequently used mercury radiotracer. Hence it is possible to obtain a similar level of performance to ²⁰³Hg when it is used it in short-term experiments and produced by the irradiation of ¹⁹⁶Hg with thermal neutrons, using mercury targets with the natural isotopic composition. However, if the 0.15% natural abundance of the ¹⁹⁶Hg isotope is increased, the specific activity of the ¹⁹⁷Hg tracer can be significantly improved. In the present work, ¹⁹⁷Hg tracer was produced from mercury 51.58% enriched in the ¹⁹⁶Hg isotope, and a 340-fold increase in specific activity with respect to natural mercury targets was obtained. When this high specific activity tracer is employed, mercury methylation and reduction experiments with minimum mercury additions are feasible. Tracer recovery in methylation experiments (associated with Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike, but also with Hg²⁺ contamination and Me¹⁹⁷Hg artefacts) with marine sediments was about 0.005% g⁻¹ WS (WS: wet sediment) after 20 h incubation with mercury additions of 0.05 ng g⁻¹ WS, which is far below natural mercury levels. In this case, the amount of Hg²⁺ reduced to Hg⁰ (expressed as the percent ¹⁹⁷Hg⁰ recovered with respect to the ¹⁹⁷Hg²⁺ added) varied from 0.13 to 1.6% g⁻¹ WS. Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike after 20 h of incubation of freshwater sediment ranged from 0.02 to 0.13% g⁻¹ WS with mercury additions of 2.5 ng g⁻¹ WS, which is also far below natural levels. ¹⁹⁷Hg⁰ recoveries were low, 0.0058 ± 0.0013% g⁻¹ WS, but showed good reproducibility in five replicates. Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spiked in freshwater samples ranged from 0.1 to 0.3% over a period of three days with mercury additions of 10 ng L⁻¹. A detection limit of 0.05% for Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike was obtained in seawater in a 25 h incubation experiment with mercury additions of 12 ng L⁻¹.     

Simultaneous determination of trace levels of ethylmercury and methylmercury in biological samples and vaccines using sodium tetra(<Emphasis Type="Italic">n</Emphasis>-propyl)borate as derivatizing agent

Because of increasing awareness of the potential neurotoxicity of even low levels of organomercury compounds, analytical techniques are required for determination of low concentrations of ethylmercury (EtHg) and methylmercury (MeHg) in biological samples. An accurate and sensitive method has been developed for simultaneous determination of methylmercury and ethylmercury in vaccines and biological samples. MeHg and EtHg were isolated by acid leaching (H₂SO₄–KBr–CuSO₄), extraction of MeHg and EtHg bromides into an organic solvent (CH₂Cl₂), then back-extraction into Milli-Q water. MeHg and EtHg bromides were derivatized with sodium tetrapropylborate (NaBPr₄), collected at room temperature on Tenax, separated by isothermal gas chromatography (GC), pyrolysed, and detected by cold-vapour atomic fluorescence spectrometry (CV AFS). The repeatability of results from the method was approximately 5–10% for EtHg and 5–15% for MeHg. Detection limits achieved were 0.01 ng g⁻¹ for EtHg and MeHg in blood, saliva, and vaccines and 5 ng g⁻¹ for EtHg and MeHg in hair. The method presented has been shown to be suitable for determination of background levels of these contaminants in biological samples and can be used in studies related to the health effects of mercury and its species in man. This work illustrates the possibility of using hair and blood as potential biomarkers of exposure to thiomersal.     

Determination of mercurial species in fish by inductively coupled plasma mass spectrometry with anion exchange chromatographic separation

This work demonstrated the feasibility of mercury speciation analysis by anion exchange chromatographic separation with inductively coupled plasma mass spectrometry detection. For the first time, by complexing with the mobile phase containing 3-mercapto-1-propanesulfonate into negatively charged complexes, fast separation of inorganic mercury (Hg²⁺), monomethylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) was achieved within 5 min on a 12.5-mm strong anion exchange column. The detection limits for Hg²⁺, MeHg, EtHg and PhHg were 0.008, 0.024, 0.029 and 0.034 μg L⁻¹, respectively. The relative standard deviations of peak height and peak area (5.0 μg L⁻¹ for each Hg species) were all below 3%. The determined contents of Hg²⁺, MeHg and total Hg in a certified reference material of fish tissue by the proposed method were in good accordance with the certified values with satisfactory recoveries. The relative errors for determining MeHg and total mercury were −2.4% and −1.2%, respectively, with an acceptable range for spike recoveries of 94–101%. Mercury speciation in 11 fish samples were then analyzed after the pretreated procedure. The mercury contents in all fish samples analyzed were found compliant with the criteria of the National Standards of China.     

Evaluating the potential and limitations of double-spiking species-specific isotope dilution analysis for the accurate quantification of mercury species in different environmental matrices

A new double-spiking approach, based on a multiple-spiking numerical methodology, has been developed and applied for the accurate quantification of inorganic mercury (IHg) and methylmercury (MeHg) by GC–ICPMS in different environmental matrices such as water, sediments and a wide range of biological tissues. For this purpose, two enriched mercury species (²⁰¹MeHg and ¹⁹⁹IHg) were added to the samples before sample preparation in order to quantify the extents of the methylation and demethylation processes, and thereby correct the final species concentrations. A critical evaluation of the applicability of this methodology was performed for each type of matrix, highlighting its main advantages and limitations when correcting for the conversion reactions of the species throughout the whole sample preparation procedure. The double-spike isotope dilution (DSIDA) methodology was evaluated by comparing it with conventional species specific isotope dilution (IDA) when analysing both certified reference materials and environmental samples (water, biotissues and sediment). The results demonstrate that this methodology is able to provide both accurate and precise results for IHg and MeHg when their relative concentrations are not too different (ratio MeHg/IHg > 0.05), a condition that holds for most natural waters and biotissues. Significant limitations on the accurate and precise determination of the demethylation factor are however observed, especially for real sediment samples in which the relative concentrations of the species are substantially different (ratio MeHg/IHg < 0.05). A determination of the sources of uncertainty in the methylation/demethylation factors has demonstrated that the accurate and precise measurement of the isotope ratios in the species involved in the transformations is crucial when quantifying the extents of these reactions. Although the double-spike methodology is established as a reference approach that permits the correction of most analytical biases and the accurate quantification of Hg species, some limitations have been identified for the first time in this work.     

Thiourea catalysis of MeHg ligand exchange between natural dissolved organic matter and a thiol-functionalized resin: a novel method of matrix removal and MeHg preconcentration for ultratrace Hg speciation analysis in freshwaters

Ultratrace analysis of dissolved MeHg in freshwaters requires both dissociation of MeHg from strong ligands in the sample matrix and preconcentration for detection. Existing solid phase extraction methods generally do not efficiently adsorb MeHg from samples containing high concentrations of natural dissolved organic matter. We demonstrate here that the addition of 10–60 mM thiourea (TU) quantitatively releases MeHg from the dissolved matrix of freshwater samples by forming a more labile complex (MeHgTU⁺) that quantitatively exchanges MeHg with thiol-functionalized resins at pH∼3.5 during column loading. The contents of these columns were efficiently eluted with acidified TU and MeHg was analyzed by Hg–TU complex ion chromatography with cold-vapor atomic fluorescence spectrometry detection. Routinely more than 90% of MeHg was recovered with good precision (average relative standard deviation of 6%) from natural waters—obtained from pools and saturated sediments of wetlands and from rivers—containing up to 68.7 mg C L⁻¹ dissolved organic matter. With the preconcentration step, the method detection limit of 0.29 pg absolute or 0.007 ng L⁻¹ in 40-mL samples is equivalent to that of the current state-of-the- art as practiced by skilled analysts. MeHg in 20–50-mL samples was completely trapped. On the basis of our knowledge of the chemistry of the process, breakthrough volume should depend on the concentrations of TU and H⁺. At a TU concentration of 12 mM breakthrough occurred between 50 and 100 mL, but overall adsorption efficiency was still 85% at 100 mL. Formation of artifactual MeHg is minimal; only about 0.7% of ambient MeHg is artifactual as estimated from samples spiked with 4 μg L⁻¹ Hg^II.     

Possible interferences of mercury sulfur compounds with ethylated and methylated mercury species using HPLC-ICP-MS

The HPLC-ICP-MS coupling technique is able to separate and detect methyl, ethyl and inorganic mercury isotopes specifically. An identification of ethyl mercury(+) is not possible when the widely used sodium tetraethylborate derivatisation method in combination with GC-AFS/AAS or ICP-MS techniques is performed because it contains ethyl groups.An unidentified compound with the same retention time as ethyl mercury was found in the HPLC chromatograms of industrial sewage samples and humic-rich soils of microcosm experiments after applying water vapour distillation. We also observed such unidentified peaks in samples of heavily contaminated sites in Eastern Germany, separated by HPLC fractionation only. In the experiments described, different mercury sulfur adducts were synthesised and tested for their retention times in the HPLC-ICP-MS system. It was found that the compound CH₃–S–Hg⁺ showed the same retention time as the ethyl mercury standard. It is therefore possible that ethyl mercury detected in chromatography by comparison of the retention time could also be due to an adduct of a sulfur compound and a mercury species. CH₃–S–Hg⁺ should be tested in other chromatographic mercury speciation methods for this effect.This work can also be regarded as a contribution to the discussion of artificially occurring methyl mercury in sediments during sample preparation.     

Label-free aptamer-based colorimetric detection of mercury ions in aqueous media using unmodified gold nanoparticles as colorimetric probe

We report a simple and sensitive aptamer-based colorimetric detection of mercury ions (Hg²⁺) using unmodified gold nanoparticles as colorimetric probe. It is based on the fact that bare gold nanoparticles interact differently with short single-strand DNA and double-stranded DNA. The anti-Hg²⁺ aptamer is rich in thymine (T) and readily forms T–Hg²⁺–T configuration in the presence of Hg²⁺. By measuring color change or adsorption ratio, the bare gold nanoparticles can effectively differentiate the Hg²⁺-induced conformational change of the aptamer in the presence of a given salt with high concentration. The assay shows a linear response toward Hg²⁺ concentration through a five-decade range of 1 × 10⁻⁴ mol L⁻¹ to 1 × 10⁻⁹ mol L⁻¹. Even with the naked eye, we could identify micromolar Hg²⁺ concentrations within minutes. By using the spectrometric method, the detection limit was improved to the nanomolar range (0.6 nM). The assay shows excellent selectivity for Hg²⁺ over other metal cations including K⁺, Ba²⁺, Ni²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺, and Fe³⁺. The major advantages of this Hg²⁺ assay are its water-solubility, simplicity, low cost, visual colorimetry, and high sensitivity. This method provides a potentially useful tool for the Hg²⁺ detection.     

An optical chemical sensor for mercury ion based on 2-mercaptopyrimidine in PVC membrane

An optical chemical sensor based on 2-mercaptopyrimidine (2-MP) in plasticized poly(vinyl chloride) (PVC) membrane incorporating (N,N-diethyl-5-(octadecanoylimino)-5H benzo[a]phenoxazine-9-amine (ETH 5294) and sodium tetraphenyl borate (NaTPB) for batch and flow-through determination of mercury ion is described. The response of the sensor is based on selective complexation of Hg²⁺ with 2-MP in the membrane phase, resulting in an ion exchange process between H⁺ in the membrane and Hg²⁺ in the sample solution. The influences of several experimental parameters, such as membrane composition, pH, and type and concentration of the regenerating reagent, were investigated. The sensor has a response range of 2.0 × 10⁻⁹ to 2.0 × 10⁻⁵ mol L⁻¹ Hg²⁺ with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹ and a response time of ≤45 s at optimum pH of 6.5 with high measurement repeatability and sensor-to-sensor reproducibility. It shows high selectivity for Hg²⁺ over several transition metal ions, including Ag⁺, Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, and common alkali and alkaline earth ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, and Pb²⁺. The sensor membrane can be easily regenerated with dilute acid solutions. The sensor has been used for the determination of mercury ion concentration in water samples.     

Solid phase extraction of trace amount of mercury from natural waters on silver and gold nanoparticles

Silver (Ag) and gold (Au) nanoparticles impregnated in nylon membrane filters have been proposed as a new solid phase for preconcentration of mercury from natural waters. Water samples were treated with KMnO₄ to convert all mercury species to inorganic Hg²⁺ and this was followed by the reduction of Hg²⁺ with NaBH₄ to elemental Hg⁰. The determination of Hg was carried out by thermal evaporation of mercury from membrane filters using Zeeman mercury analyzer RA–915+ (Lumex, Russia). This process does not involve any additional sample treatment and sharply reduces risk of samples contamination. The limit of detection (LOD) was found to be 0.04 ng (absolute mass). Relative LOD was 0.4 ng L⁻¹ for 100 mL of water. The method was validated through the analysis of CRM NRCC Tort–2 (Lobster hepatopancreas) and the found value (0.30 ± 0.07 μg g⁻¹) was in good agreement with the certified value (0.27 ± 0.06 μg g⁻¹). High efficiency of Hg accumulation from aqueous phase to membrane filters can be attributed to a large surface area of nanoparticles.     

Online anion exchange column preconcentration and high performance liquid chromatographic separation with inductively coupled plasma mass spectrometry detection for mercury speciation analysis

A hyphenated method for mercury speciation analysis by the coupling of high performance liquid chromatography and inductively coupled plasma mass spectrometry with the online strong anion exchange column (SAX) preconcentration was developed. The Hg analytes (Hg⁺, MeHg, EtHg and Hg²⁺) were absorbed on the SAX column preconditioned with sodium 3-mercapto-1-propanesulfonate, and then rapidly eluted (less than 16 s) by 5 μL 3% (v/v) 2-mercaptoethanol. The enrichment factors of 1025 for Hg⁺, 1084 for MeHg, 1108 for EtHg and 1046 for Hg²⁺ were obtained using 6 mL sample in a 1.5-min enrichment procedure. Rapid separation of the four mercurial compounds was achieved within 5 min on a 50-mm C₁₈ column using 0.5% (v/v) 2-mercaptoethanol as the mobile phase. The detection limits for Hg⁺, MeHg, EtHg and Hg²⁺ were 0.015, 0.010, 0.009 and 0.016 ng L⁻¹, each, and the relative standard deviations of peak height and peak area (5 ng L⁻¹ for each Hg species) were all below 5%. Mercury speciation in three freshwater, two drinking water and two seawater samples were then analyzed by the proposed method. MeHg and Hg²⁺ concentrations down to 0.14 and 0.56 ng L⁻¹ were detected in the drinking waters.     

A Simple Fluorometric Method Using Chlorophyll a for Determination of Hg2+ Ion

A simple and green analytical procedure based on chlorophyll a is presented for the determination of Hg²⁺ ion. Chlorophyll a was extracted and purified from the leaves of pea and is employed as a reagent for analysis of Hg²⁺ ion. It displays remarkable fluorescence emission at 674 nm when excited at 412 nm. The emission intensity decreased significantly on exposure to various concentrations of Hg²⁺ ion. This forms the basis for the determination of Hg²⁺ ion. The proposed method was evaluated for sensitivity and selectivity. The linear concentration range was found to be 2.0–10 μM with r² = 0.997 and the limit of detection for Hg²⁺ ion was 1.3 μM. Ions including Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ru³⁺, Er³⁺, K⁺, Na⁺, NH₄⁺, Cl⁻, NO₃⁻, CH₃COO⁻ and SO₄²⁻ did not interfere with the measurement of Hg²⁺ ion even at 500-fold excess. Since chlorophyll a is widely available in the leaves of most plants, and the extraction and purification process is simple, this technique can provide an alternative, sensitive and economical way to determine Hg²⁺ ion.     

Comparison of Pyrolysis and Microwave Acid Digestion Techniques for the Determination of Mercury in Biological and Environmental Materials

 Microwave digestion reduction-aeration and pyrolysis combined with cold vapour atomic absorption and cold vapour atomic fluorescence are compared for the determination of total mercury in several biological and environmental matrices. The biological samples were digested in a mixture of HNO₃/H₂O₂, the environmental samples in a mixture of HNO₃/HClO₄. After reduction with SnCl₂, the mercury was collected by two-stage gold amalgamation. After microwave digestion reduction-aeration, detection limits of 1.4 ng g⁻¹ and 0.6 ng g⁻¹ were obtained for cold vapour atomic absorption spectrometry (CVAAS) and cold vapour atomic fluorescence spectrometry (CVAFS), respectively, for 250 mg of environmental samples. For biological samples (500 mg) the detection limits were 0.7 ng g⁻¹ (CVAAS) and 0.4 ng g⁻¹ (CVAFS). After pyrolysis, detection limits of 3.5 ng g⁻¹ and 1.6 ng g⁻¹ for CVAAS and CVAFS, respectively, were obtained for a 10 mg sample. Pyrolysis can only be applied when the organic content of the sample is not too high. Accurate results were obtained for 8 certified reference materials of both environmental and biological origin. In addition, a real sludge sample was analysed. Author for correspondence. E-mail: richard.dams@rug.ac.be Received September 18, 2002; accepted December 3, 2002 Published online May 5, 2003     

Mercury speciation analysis in seafood by species-specific isotope dilution: method validation and occurrence data

Methylmercury (MeHg) and total mercury (THg) in seafood were determined using species-specific isotope dilution analysis and gas chromatography combined with inductively coupled plasma mass spectrometry. Sample preparation methods (extraction and derivation step) were evaluated on certified reference materials using isotopically enriched Hg species. Solid–liquid extraction, derivation by propylation and automated agitation gave excellent accuracy and precision results. Satisfactory figures of merit for the selected method were obtained in terms of limit of quantification (1.2 μg Hg kg⁻¹ for MeHg and 1.4 μg Hg kg⁻¹ for THg), repeatability (1.3–1.7%), intermediate precision reproducibility (1.5% for MeHg and 2.2% for THg) and trueness (bias error less than 7%). By means of a recent strategy based on accuracy profiles (β-expectation tolerance intervals), the selected method was successfully validated in the range of approximately 0.15–5.1 mg kg⁻¹ for MeHg and 0.27–5.2 mg kg⁻¹ for THg. Probability β was set to 95% and the acceptability limits to ±15%. The method was then applied to 62 seafood samples representative of consumption in the French population. The MeHg concentrations were generally low (1.9–588 μg kg⁻¹), and the percentage of MeHg varied from 28% to 98% in shellfish and from 84% to 97% in fish. For all real samples tested, methylation and demethylation reactions were not significant, except in one oyster sample. The method presented here could be used for monitoring food contamination by MeHg and inorganic Hg in the future to more accurately assess human exposure.     

Photo-induced cold vapor generation with low molecular weight alcohol, aldehyde, or carboxylic acid for atomic fluorescence spectrometric determination of mercury

With UV irradiation, Hg²⁺ in aqueous solution can be converted into Hg⁰ cold vapor by low molecular weight alcohols, aldehydes, or carboxylic acids, e.g., methanol, formaldehyde, acetaldehyde, glycol, 1,2-propanediol, glycerol, acetic acid, oxalic acid, or malonic acid. It was found that the presence of nano-TiO₂ more or less improved the efficiency of the photo-induced chemical/cold vapor generation (photo-CVG) with most of the organic reductants. The nano-TiO₂-enhanced photo-CVG systems can be coupled to various analytical atomic spectrometric techniques for the determination of ultratrace mercury. In this work, we evaluated the application of this method to the atomic fluorescence spectrometric (AFS) determination of mercury in cold vapor mode. Under the optimized experimental conditions, the instrumental limits of detection (based on three times the standard deviation of 11 measurements of a blank solution) were around 0.02–0.04 μg L⁻¹, with linear dynamic ranges up to 15 μg L⁻¹. The interference of transition metals and the mechanism of the photo-CVG are briefly discussed. Real sample analysis using the photo-CVG-AFS method revealed that it was promising for water and geological analysis of ultralow levels of mercury. Image of the photo-CVG instrumentation showing the photoreactor inside the water cooling unit     

Determination of total mercury and methylmercury in biological samples by photochemical vapor generation

Cold vapor atomic absorption spectrometry (CV-AAS) based on photochemical reduction by exposure to UV radiation is described for the determination of methylmercury and total mercury in biological samples. Two approaches were investigated: (a) tissues were digested in either formic acid or tetramethylammonium hydroxide (TMAH), and total mercury was determined following reduction of both species by exposure of the solution to UV irradiation; (b) tissues were solubilized in TMAH, diluted to a final concentration of 0.125% m/v TMAH by addition of 10% v/v acetic acid and CH₃Hg⁺ was selectively quantitated, or the initial digests were diluted to 0.125% m/v TMAH by addition of deionized water, adjusted to pH 0.3 by addition of HCl and CH₃Hg⁺ was selectively quantitated. For each case, the optimum conditions for photochemical vapor generation (photo-CVG) were investigated. The photochemical reduction efficiency was estimated to be ∼95% by comparing the response with traditional SnCl₂ chemical reduction. The method was validated by analysis of several biological Certified Reference Materials, DORM-1, DORM-2, DOLT-2 and DOLT-3, using calibration against aqueous solutions of Hg²⁺; results showed good agreement with the certified values for total and methylmercury in all cases. Limits of detection of 6 ng/g for total mercury using formic acid, 8 ng/g for total mercury and 10 ng/g for methylmercury using TMAH were obtained. The proposed methodology is sensitive, simple and inexpensive, and promotes “green” chemistry. The potential for application to other sample types and analytes is evident.     

Ultrasound-assisted vapor generation of mercury

Cold vapor generation arising from reduction of both Hg²⁺ and CH₃Hg⁺ occurs using ultrasonic (US) fields of sufficient density to achieve both localized heating as well as radical-based attack in solutions of formic and acetic acids and tetramethylammonium hydroxide (TMAH). A batch sonoreactor utilizing an ultrasonic probe as an energy source and a flow through system based on a US bath were optimized for this purpose. Reduction of CH₃Hg⁺ to Hg⁰ occurs only at relatively high US field density (>10 W cm⁻³ of sample solution) and is thus not observed when a conventional US bath is used for cold vapor generation. Speciation of mercury is thus possible by altering the power density during the measurement process. Thermal reduction of Hg²⁺ is efficient in formic acid and TMAH at 70 °C and occurs in the absence of the US field. Room temperature studies with the batch sonoreactor reveal a slow reduction process, producing temporally broad signals having an efficiency of approximately 68% of that arising from use of a conventional SnCl₂ reduction system. Molecular species of mercury are generated at high concentrations of formic and acetic acid. Factors affecting the generation of Hg⁰ were optimized and the batch sonoreactor used for the determination of total mercury in SLRS-4 river water reference material.     

Determination of compound-specific Hg isotope ratios from transient signals using gas chromatography coupled to multicollector inductively coupled plasma mass spectrometry (MC-ICP/MS)

MeHg and inorganic Hg compounds were measured in aqueous media for isotope ratio analysis using aqueous phase derivatization, followed by purge-and-trap preconcentration. Compound-specific isotope ratio measurements were performed by gas chromatography interfaced to MC-ICP/MS. Several methods of calculating isotope ratios were evaluated for their precision and accuracy and compared with conventional continuous flow cold vapor measurements. An apparent fractionation of Hg isotopes was observed during the GC elution process for all isotope pairs, which necessitated integration of signals prior to the isotope ratio calculation. A newly developed average peak ratio method yielded the most accurate isotope ratio in relation to values obtained by a continuous flow technique and the best reproducibility. Compound-specific isotope ratios obtained after GC separation were statistically not different from ratios measured by continuous flow cold vapor measurements. Typical external uncertainties were 0.16‰ RSD (n = 8) for the ²⁰²Hg^/198Hg ratio of MeHg and 0.18‰ RSD for the same ratio in inorganic Hg using the optimized operating conditions. Using a newly developed reference standard addition method, the isotopic composition of inorganic Hg and MeHg synthesized from this inorganic Hg was measured in the same run, obtaining a value of δ ²⁰²Hg = −1.49 ± 0.47 (2SD; n = 10). For optimum performance a minimum mass of 2 ng per Hg species should be introduced onto the column.     

Capillary electrophoretic determination of mercury compounds in different matrixes

Summary Capillary electrophoresis has been used to separate inorganic (Hg²⁺) and organic (methyl-, ethyl-, and phenylmercury) mercury compounds as their cysteine complexes. The optimized electrophoretic separation was performed in fused-silica capillary tubing at 25 kV with 25mm sodium borate buffer (pH 9.3). Identification and quantification of the mercury species at mg L⁻¹ levels was achieved by use of UV detection at 200 nm. The relative standard deviation (n=10) ranged from 0.38 to 0.51% for migration times and from 0.43 to 2.94% for corrected peak areas. Good recovery (>90%) was obtained for all four mercury species in surface waters, and for inorganic mercury and methylmercury in five- to tenfold diluted biofluids (urine, saliva, and cerebrospinal fluid). TheLOQ values obtained were too high to be useful for determination of mercury species in real samples. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Preconcentration and speciation of inorganic and methyl mercury in waters using polyaniline and gold trap-CVAAS

Applicability of polyaniline (PANI) has been investigated for the preconcentration and speciation of inorganic mercury (Hg²⁺) and methyl mercury (CH₃Hg⁺) in various waters (ground, lake and sea waters). Preliminary experiments (batch) with powdered PANI for the quantitative removal of both Hg²⁺ and CH₃Hg⁺ showed that the retention of Hg²⁺ was almost independent of pH while a pH dependent trend from pH 1 to 12 was seen for CH₃Hg⁺ with maximum retention at pH > 5. Time dependence batch studies showed that a contact time of 10 min was sufficient to reach equilibrium. The K_d values were found to be ∼8 × 10⁴ and ∼7 × 10³ for Hg²⁺ and CH₃Hg⁺, respectively.Subsequently column experiments were carried out with PANI and the separation of the species was carried out by selective and sequential elution with 0.3% HCl for CH₃Hg⁺ and 0.3% HCl-0.02% thiourea for Hg²⁺. This was then followed by further pre-concentration of mercury on a gold trap and its determination by CVAAS. The uptake efficiency studies showed that the PANI column was able to accumulate up to 100 mg Hg²⁺/g and 2.5 mg CH₃Hg⁺/g. This method allows both preconcentration and speciation of mercury with preconcentration factors around 120 and 60 for Hg²⁺ and CH₃Hg⁺, respectively. The interfering effects of various foreign substances on the retention of mercury were investigated.     

Analytical approach for routine methylmercury determination in seafood using gas chromatography-atomic fluorescence spectrometry

Two methodologies have been developed for the analysis of mercury species in seafood by capillary gas chromatography coupled to an AFS detector via pyrolysis. The first one is based on the ethylation of both, inorganic and methylmercury species (Method 1), in which clean-up is not necessary because a small amount of sample is required. In the second one, monoalkylated mercury species are extracted into organic phases after forming the corresponding chlorides (Method 2). In this case the elimination of the interfering compounds from the matrix requires a clean-up step, which enables the treatment of higher quantities of sample. Both procedures can be considered complementary because the concentration range applicable for each one of them is different: 0.75-10 μg_Hg g⁻¹, in dry basis for methylmercury (Method 1) and 6-1000 ng_Hg g⁻¹ (Method 2). The range of application for natural samples can be easily selected by a preliminary analysis of total mercury, because most mercury in seafood is present as MeHg. Optimum parameters for both procedures have been evaluated, and the methods were validated with two standard reference materials (BCR-463 and NIST-2977). Finally, the methods have been applied to the analysis of seafood samples. Detection limits of MeHg range from 1.7 to 220 ng_Hg g⁻¹ (dry basis) depending of the methodology selected and the weight of sample. The method can be successfully applied to commercially available seafood samples, and considered for routine analysis.