Application of speciated isotope dilution mass spectrometry to evaluate extraction methods for determining mercury speciation in soils and sediments

Extraction techniques commonly used to extract methylmercury or mercury species from various matrixes have been evaluated regarding their potential to transform inorganic mercury to methylmercury, or vice versa, during sample preparation steps by applying speciated isotope dilution mass spectrometry. Two of the five tested methods were highly prone to form inorganic mercury from methylmercury. Some published methods converted methylmercury to inorganic mercury approximately 100% (including the spiked CH(3)(201)Hg(+)). In other methods, as much as 45% of methylmercury was converted to inorganic mercury during extraction. The methods evaluated included cold acid extraction and sonication. Other methods, such as the proposed EPA RCRA Draft Method 3200, microwave-assisted extraction, and another sonication-based methods induced very little or no methylmercury transformation to inorganic mercury. Among these three methods, the proposed Draft EPA Method 3200 was found to be the most efficient.     

Use of a solution cathode glow discharge for cold vapor generation of mercury with determination by ICP-atomic emission spectrometry

A novel vapor-generation technique is described for mercury determination in aqueous solutions. Without need for a chemical reducing agent, dissolved mercury species are converted to volatile Hg vapor in a solution cathode glow discharge. The generated Hg vapor is then transported to an inductively coupled plasma for determination by atomic emission spectrometry. Mercury vapor is readily generated from a background electrolyte containing 0.1 M HNO 3. Vapor generation efficiency was found to be higher by a factor of 2-3 in the presence of low molecular weight organic acids (formic or acetic acids) or alcohols (ethanol). Optimal conditions for discharge-induced vapor generation and reduced interference from concomitant inorganic ions were also identified. However, the presence of chloride ion reduces the efficiency of Hg-vapor generation. In the continuous sample introduction mode, the detection limit was found to be 0.7 microg L (-1), and repeatability was 1.2% RSD ( n = 11) for a 20 microg L (-1) standard. In comparison with other vapor generation methods, it offers several advantages: First, it is applicable to both inorganic and organic Hg determination; organic mercury (thiomersal) can be directly transformed into volatile Hg species without the need for prior oxidation. Second, the vapor-generation efficiency is high; the efficiency (with formic acid as a promoter) is superior to that of conventional SnCl 2-HCl reduction. Third, the vapor generation is extremely rapid and therefore is easy to couple with flow injection. The method is sensitive and simple in operation, requires no auxiliary reagents, and serves as a useful alternative to conventional vapor generation for ultratrace Hg determination.     

Using speciated isotope dilution with GC-inductively coupled plasma MS to determine and unravel the artificial formation of monomethylmercury in certified reference sediments

Speciated isotope-dilution mass spectrometry (SID-MS) is claimed to be an absolute method; however, it has been found to be affected by artifact monomethylmercury (MMHg) formation in sediments. The determination of MMHg 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 (CGC). Isotope ratios (peak area ratios at different masses) were measured by on-line ICP-MS detection of the CGC-separated compounds. Reproducibility of 202Hg/201Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for Et2Hg; for 202Hg/199Hg, 0.43 and 0.46%, respectively, were determined. The absolute detection limits for CGC-ICPMS measurements were better than 26 fg for 202Hg, 20 fg for 201Hg, and 24 fg for 199Hg. For the direct determination of MMHg 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 localize the sources of the unintentional abiotic methylmercury formation during analysis. Different spiking and derivatization procedures (either ethylation, propylation, or derivatization 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 cleanup steps was applied in order to reduce high Hg2+ amounts. The method was applied to the determination of MMHg 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 sulfur contents. The results obtained confirmed that available sediment reference materials are adequate to achieve traceable mercury speciation analysis and to detect potential sources of MMHg artifact formation.     

The capillary cold trap as a suitable instrument for mercury speciation by volatilization, cryogenic trapping, and gas chromatography coupled with atomic absorption spectrometry

An innovative accessory for speciation analysis has been developed. The system is based on the combination of cryogenic trapping and gas chromatographic separation, carried out within the same capillary. The instrument, hyphenating derivatization, gas-phase extraction, preconcentration, and analyte separation, is semiautomated, and all operational parameters are adjustable via an in-house-developed control unit, which regulates the selected parameters throughout the analysis process. Species detection was carried out by atomic absorption spectrometry. The detection limits achieved were 33, 39, and 71 ng L(-1) for dimethylmercury, methylmercury, and inorganic mercury, respectively. A complete chromatogram could be obtained within three minutes, resulting in the duration of one whole analysis cycle of about 15 min. The proposed method was applied to mercury speciation in freeze-dried tuna fish powder after microwave-assisted extraction, finding that mercury is present at 80% as methylmercury and about 20% as inorganic mercury, in this kind of biological material.     

Sequential flow injection analysis system on-line coupled to high intensity focused ultrasound: green methodology for trace analysis applications as demonstrated for the determination of inorganic and total mercury in waters and urine by cold vapor atomic absorption spectrometry

A new concept is presented for green analytical applications based on coupling on-line high-intensity focused ultrasound (HIFU) with a sequential injection/flow injection analysis (SIA/FIA) system. The potential of the SIA/HIFU/FIA scheme is demonstrated by taking mercury as a model analyte. Using inorganic mercury, methylmercury, phenylmercury, and diphenylmercury, the usefulness of the proposed methodology for the determination of inorganic and total mercury in waters and urine was demonstrated. The procedure requires low sample volumes and reagents and can be further applied to all chemical reactions involving HIFU. The inherent advantages of SIA, FIA, and HIFU applications in terms of high throughput, automation, low reagent consumption, and green chemistry are accomplished together for the first time in the present work.     

Room temperature sonolysis-based advanced oxidation process for degradation of organomercurials: application to determination of inorganic and total mercury in waters by flow injection-cold vapor atomic absorption spectrometry

A new oxidation method based on room-temperature ultrasonic irradiation (sonolysis) is proposed for conversion of organomercurials into inorganic mercury and subsequent determination by flow injection-cold vapor atomic absorption spectrometry. This advanced oxidation process eliminates the need for chemical oxidants, high temperature, and pressure for degradation of organomercurials so that total mercury can be determined with sodium tetrahydroborate(III) or tin(II) chloride as reducing agents. Complete oxidations can be accomplished within 3 min, using a 40% sonication amplitude (100 W nominal power) provided by a probe ultrasonic device (20 kHz frequency) and a 1 mol L(-1) HCl liquid medium. The presence of HCl was seen to be necessary for fast oxidation of organomercurials, in contrast to other chemical oxidants such as H2O2 or HNO3 which yielded incomplete oxidation. Further advantages of the proposed method over existing methods which are currently employed for oxidation prior to total Hg determination are the removal of hazardous wastes and the decreased risk of Hg losses by volatilization. Oxidation kinetics indicated a pseudofirst-order reaction with apparent rate constants (k) of 3.2 x 10(-2) and 1.6 x 10(-2) s(-1) for methylmercury and phenylmercury, respectively. Oxidation experiments in the presence of foreign substances acting as OH radical scavengers showed a tolerance at least up to a concentration of 1000 mg L(-1). Likewise, model wastewaters with chemical oxygen demand of up to 1000 mg L(-1) could be processed without diminishing the oxidation efficiency. The method was applied to determination of inorganic and total mercury in simulated wastewaters and spiked environmental waters in combination with selective reduction.     

On-line preconcentration and determination of mercury in biological and environmental samples by cold vapor-atomic absorption spectrometry

An on-line procedure for the determination of traces of total mercury in environmental and biological samples is described. The present methodology combines cold vapor generation associated to atomic absorption spectrometry (CV-AAS) with preconcentration of the analyte on a minicolumn packed with activated carbon. The retained analyte was quantitatively eluted from the minicolumn with nitric acid. After that, volatile specie of mercury was generated by merging the acidified sample and sodium tetrahydroborate(III) in a continuous flow system. The gaseous analyte was subsequently introduced via a stream of Ar carrier into the atomizer device. Optimizations of both, preconcentration and mercury volatile specie generation variables were carried out using two level full factorial design (2(3)) with 3 replicates of the central point. Considering a sample consumption of 25mL, an enrichment factor of 13-fold was obtained. The detection limit (3sigma) was 10ngL(-1) and the precision (relative standard deviation) was 3.1% (n=10) at the 5microgL(-1) level. The calibration curve using the preconcentration system for mercury was linear with a correlation coefficient of 0.9995 at levels near the detection limit up to at least 1000microgL(-1). Satisfactory results were obtained for the analysis of mercury in tap water and hair samples.     

Development, validation, and application of a method for quantification of methylmercury in biological marine materials using gas chromatography atomic emission detection

A gas chromatographic method was developed for the quantification of alkylmercury species using microwave-induced plasma atomic emission detection (GC-AED). The column conditioning and analyte derivatization required for previous methods were found to be unnecessary for stable, accurate, and sensitive element-specific detection using GC-AED. Chromatographic and detection parameters such as stationary phase type, stationary phase film thickness, GC column dimensions, helium mobile phase column head pressure, detector makeup gas flow rate, and detector reagent gas type and flow rate were found to significantly affect analyte response. The detection limit for the optimized GC-AED conditions was 0.8 pg (0.1 pg/s) of methylmercury chloride (as mercury). A solid-liquid extraction procedure with preparative gel permeation chromatography cleanup and GC-AED analysis was used to quantify methylmercury in a variety of complex matrix marine materials. The methylmercury quantification method was validated with four marine certified reference materials (CRMs). The method was then applied to 13 standard reference materials, CRMs, and control materials for which no certified reference values for methylmercury have been determined. Four National Institute of Standards and Technology Standard Reference Materials and one control material, which were analyzed using the GC-AED method, were also analyzed by two other laboratories using independent methods to further validate the method.     

Validation of methylmercury determinations in aquatic systems by alkyl derivatization methods for GC analysis using ICP-IDMS

Isotope dilution mass spectrometry (IDMS), using an inductively coupled plasma quadrupole mass spectrometer (ICPMS) and a species-specific methylmercury spike was applied to validate the commonly used GC method for methylmercury (MeHg+) determination, which is based on the formation of volatile methylethylmercury by derivatizationwith NaBEt4. The spike compound, Me201Hg+, was synthesized by reaction of 201Hg-enriched mercury chloride with methylcobalamin. By analyzing different environmental aquatic samples, it was found that in most cases, transformation of MeHg+ into elemental mercury (Hg0) took place. From investigations of synthetic solutions, it could be followed that halide ions are responsible for this transformation process. Chloride and bromide converted MeHg+ into Hg0, whereas iodide caused transformation into Hg2+ and Hg0. It could also be shown that transformation of MeHg+ took place only during the derivatization step. In contrast to ethylation, propylation by NaBPr4 did not cause any transformation; however, accurate results of MeHg+ determinations could be obtained by propylation as well as by ethylation when GC/ ICP-IDMS was applied. This work demonstrates the great power of isotopically labeled element compounds for the validation of element speciation methods and for species-specific IDMS analyses.     

Selective measurement of ultratrace methylmercury in fish by flow injection on-line microcolumn displacement sorption preconcentration and separation coupled with electrothermal atomic absorption spectrometry

A novel nonchromatographic speciation technique for ultratrace methylmercury in biological materials was developed by flow injection microcolumn displacement sorption preconcentration and separation coupled on-line with electrothermal atomic absorption spectrometry (ETAAS). In the developed technique, Cu(II) was first on-line complexed with diethyldithiocarbamate (DDTC), and the resultant Cu-DDTC was presorbed onto a microcolumn packed with the sorbent from a cigarette filter. Selective preconcentration of methylmercury (MeHg) in the presence of Hg(II), ethylmercury (EtHg), and phenylmercury (PhHg) was achieved at pH 6.8 through loading the sample solution onto the microcolumn due to a displacement reaction between MeHg and the presorbed Cu-DDTC. The retained MeHg was subsequently eluted with 50 microL of ethanol and on-line determined by ETAAS. Interferences from coexisting heavy metal ions with lower stability of their DDTC complexes relative to Cu-DDTC were minimized without the need of any masking reagents. No interferences from 5.5 mg L(-1) Cu(II), 4.5 mg L(-1) Cd(II), 2.5 mg L(-1) Cr(III), 3 mg L(-1) Fe(III), 10 mg L(-1) Ni(II), 10 mg L(-1) Pb(II), and at least 25 mg L(-1) Zn(II) were observed for the determination of MeHg at the 50 ng L(-1) level (as Hg). With the consumption of only 3.4 mL of sample solution, an enhancement factor of 75, a detection limit of 6.8 ng L(-1) (as Hg) in the digest (corresponding to 3.4 ng g(-1) in original solid sample for a final 50 mL of digest of 0.1 g of solid material), and a precision (RSD, n = 13) of 2.3% for the determination of methylmercury at the 50 ng L(-1) (as Hg) level were achieved at a sample throughput of 30 samples h(-1). The recoveries of methylmercury spike in real fish samples ranged from 97 to 108%. The developed technique was validated by determination of methylmercury in a certified reference material (DORM-2, dogfish muscle), and was shown to be useful for the determination of methylmercury in real fish samples.     

Preconcentration, speciation and determination of ultra trace amounts of mercury by modified octadecyl silica membrane disk/electron beam irradiation and cold vapor atomic absorption spectrometry

Mercury (II) and methyl mercury cations at the Sub-ppb level were adsorbed quantitatively from aqueous solution onto an octadecyl-bonded silica membrane disk modified by 2-[(2-mercaptophyenylimino)methyl] phenol (MPMP). The trapped mercury was then eluted with 3ml ethanol and Hg2+ ion was directly measured by cold vapor atomic absorption spectrometry, utilizing tin (II) chloride. Total mercury (Hgt) was determined after conversion of MeHg+ into Hg2+ ion by electron beam irradiation. A sample volume of 1500ml resulted in a preconcentration factor of 500 and the precision for a sampling volume of 500ml at a concentration of 2.5microgl(-1) (n=7) was 3.1%. The limit of detection of the proposed method is 3.8ngl(-1). The method was successfully applied to analysis of water samples, and the accuracy was assessed via recovery experiment.     

Determination of mercury in ash and soil samples by oxygen flask combustion method--cold vapor atomic fluorescence spectrometry (CVAFS)

A simple method was developed for the determination of mercury (Hg) in coal fly ash (CFA), waste incineration ash (WIA), and soil by use of oxygen flask combustion (OFC) followed by cold vapor atomic fluorescence spectrometry (CVAFS). A KMnO4 solution was used as an absorbent in the OFC method, and the sample containing a combustion agent and an ash or soil sample was combusted by the OFC method. By use of Hg-free graphite as the combustion agent, the determination of Hg in ash and soil was successfully carried out; the Hg-free graphite was prepared by use of a mild pyrolysis procedure at 500 degrees C. For six certified reference materials (three CFA samples and three soil samples), the values of Hg obtained by this method were in good agreement with the certified or reference values. In addition, real samples including nine CFAs collected from some coal-fired power plants, five WIAs collected from waste incineration plants, and two soils were analyzed by the present method, and the data were compared to those from microwave-acid digestion (MW-AD) method.     

Hg(0) oxidative absorption by K(2)S(2)O(8) solution catalyzed by Ag(+) and Cu(2+)

The aqueous phase oxidation of gaseous elemental mercury (Hg(0)) by potassium persulfate (K(2)S(2)O(8), KPS) catalyzed by Ag(+) and Cu(2+) was investigated using a glass bubble column reactor. Concentrations of gaseous Hg(0) and aqueous Hg(2+) were measured by cold vapor generation atomic absorption spectrometry (CVAAS). The effects of several experimental parameters on the oxidation were studied; these include different types of catalysts, pHs and concentrations of potassium persulfate, temperatures, Hg(0) inlet concentrations and tertiary butanol (TBA). The results showed that the removal efficiency of Hg(0) increased with increasing concentration of potassium persulfate and catalysts Ag(+), Cu(2+) and Ag(+) provided better catalytic effect than Cu(2+). For example, in the presence of 5.0mmoll(-1) KPS, the mercury removal efficiency could reach 75.4 and 97.0% for an Ag(+) concentration of 0.1 and 0.3mmoll(-1), respectively, and 69.8 and 81.9% for 0.1 and 0.3mmoll(-1) Cu(2+). On the other hand, high temperature and the introduction of TBA negatively affect the oxidation. Furthermore, the removal efficiency of Hg(0) was much greater in neutral solution than in either acidic or alkaline solution. But the influence of pH was almost eliminated upon the addition of Ag(+) and Cu(2+), and high Hg(0) inlet concentration also has positive impact on the removal efficiency of Hg(0). The possible catalytic oxidation mechanism of gaseous mercury by KPS was also proposed.     

气态元素汞校准的一致性光学评定检测实验研究

利用低压汞灯作为光源,结合单色仪,对汞渗透管法和汞饱和蒸气法气态元素汞校准进行一致性光学评定检测研究。在汞渗透管实验中,吸收度面积值与理论浓度的皮尔逊相关系数为0.996 8,拟合优度为0.993 6,说明两组数据相关性较好且符合郎伯比尔定律。取实验的吸收截面作为标准参考吸收截面,对相同浓度汞蒸气横向对比及不同浓度汞蒸气纵向对比,浓度误差最大为7.45%,表明渗透管法的稳定性较好且精度较高,验证了渗透管法作为汞标气法的可行性。在渗透管实验中加入SO₂,气态汞浓度测量误差最大为12.82%,说明SO₂对汞吸收度测量产生一定程度的干扰。汞饱和蒸气法实验中,以渗透管为基准测得的最大误差在标准允许误差之内,表明2种校准方法具有一致性。但汞饱和蒸气法与渗透管法相比,其重复性及精度仍有不足,待提升空间较大。     

Probing mercury species-DNA interactions by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection

The interactions of inorganic mercury Hg(II), methylmercury (MeHg(I)), ethylmercury (EtHg(I)), and phenylmercury (PhHg(I)) with DNA have been probed by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection (CE-ETAAS) in combination with circular dichroism and Fourier transform infrared spectroscopy. The CE-ETAAS assay allows sensitive probing of the level of DNA damage by mercury species, extraction of thermodynamic and kinetic information on the interactions of mercury species with DNA, and provides direct evidence for the formation of mercury species-DNA adducts. The binding affinity of mercury species to DNA increases in order of Hg(II) < EtHg(I) approximately PhHg(I) approximately MeHg(I). The interactions of mercury species with DNA follow a first-order kinetics for mercury species and zero-order kinetics for DNA. Mercury highly covalently coordinates to endocyclic and exocyclic N sites of DNA bases. However, the interactions of DNA with mercuric species cause no transition of the DNA original conformation. The results reveal that organomercuric species exhibit stronger affinity and faster binding to DNA and show more potential damage to DNA than Hg(II) in view of the kinetic and thermodynamic evaluations. Moreover, MeHg(I) exhibits the fastest binding to DNA, suggesting that MeHg(I) enjoys superiority over the other mercuric species for rapid formation of a stable complex with DNA, whereas Hg(II) shows the slowest binding to DNA. The present study provides new evidence and understanding of the binding modality of mercuric species to DNA.     

Slurry sampling in serum blood for mercury determination by CV-AFS

The heavy metal mercury (Hg) is a neurotoxin known to have a serious health impact even at relatively low concentrations. A slurry method was developed for the sensitive and precise determination of mercury in human serum blood samples by cold vapor generation coupled to atomic fluorescence spectrometry (CV-AFS). All variables related to the slurry formation were studied. The optimal hydrochloric concentration and tin(II) chloride concentration for CV generation were evaluated. Calibration within the range 0.1-10 microg L(-1) Hg was performed with the standard addition method, and compared with an external calibration. Additionally, the reliability of the results obtained was evaluated by analyzing mercury in the same samples, but submitted to microwave-assisted digestion method. The limit of detection was calculated as 25 ng L(-1) and the relative standard deviation was 3.9% at levels around of 0.4 microg L(-1)Hg.     

Detection of organomercurials with sensor bacteria.

Mercury and its organic compounds, especially methylmercury, are hazardous compounds that concentrate in biota via biomagnification and cause severe neurological disorders in animals. In this paper, a recombinant whole-cell bacterial sensor for the detection of the organic compounds of mercury was constructed. The sensor carries firefly luciferase gene as a reporter under the control of the mercury-inducible regulatory part of broad spectrum mer operon from pDU1358. In addition, a gene-encoding organomercurial lyase (an enzyme necessary for cleavage of the mercury-carbon bond) was coexpressed in the sensor strain. The sensitivity of the sensor was evaluated on some environmentally important organomercurial compounds. The lowest detectable concentrations were 0.2 nM (50 ng/L), 1 nM (0.34 microg/L), and 10 microM (2.3 mg/L) for methylmercury chloride, phenylmercury acetate, and dimethylmercury, respectively. The sensor responded also to inorganic mercury and, therefore, using the sensor described here together with sensor bacteria responding only to inorganic mercury, it should be possible to characterize the mercury contamination, for example, in environmental samples.     

HPLC-ICP-MS法测定水样中的甲基汞、乙基汞和无机汞

建立了高效液相色谱(HPLC)和电感耦合等离子体质谱(ICP-MS)联用测定环境水样中的甲基汞、乙基汞和无机汞的方法。实验使用的高效液相色谱流动相为含有0.06mol/L乙酸氨,20μg/LBi,0.1%(V/V)2-巯基乙醇的5%(V/V)甲醇-水溶液,色谱柱为C18反相柱(5μm,2.1mm×50mm),经前处理的水样在液相色谱中分离后,进入电感耦合等离子体质谱检测其甲基汞、乙基汞和无机汞的浓度。甲基汞、乙基汞和无机汞检出限分别为0.05μg/L、0.10μg/L和0.10μg/L。     

Determination of total mercury in water and urine by a gold film sensor following Fenton's reagent digestion

Fenton's reagent (Fe(II) + H2O2) is utilized for the digestion of environmental water samples and urine. Following the digestion, which converts organic forms of Hg to inorganic Hg(II), Hg(0) is liberated by borohydride reduction and measured by a conductometric gold film sensor. Quantitative recovery of Hg from samples spiked with mercuric chloride, methylmercury(II) chloride, and phenylmercury(II) acetate was attainable in the presence of naturally occurring suspended matter and humic and fulvic acids as well as 3% NaCl. The digestion is performed at moderate pH (3-4) and temperature (less than or equal to 50 degrees C) and does not use large amounts of any reagent. Excellent agreement is shown for reference water, wastewater, and urine standards. The limit of detection, facilitated by the low blank value, is 500 pg of Hg or 10 ng/L for a 50-mL sample.     

A device for sampling and determination of total particulate mercury in ambient air

A miniaturized device, which serves as both particulate trap and pyrolyzer for airborne particulate mercury species, is described. It has been used in combination with amalgamation/thermal desorption/cold vapor atomic fluorescence spectrometry detection for the determination of total particulate mercury (TPM) associated with atmospheric aerosols. A standard reference material (SRM 1633b, NIST) has been used for validating of the pyrolysis technique, and a relative error smaller than 3% has been obtained. Contrary to most methods currently employed, this new technique does not require any sample preparation (e.g., extraction/digestion), no manual sample transfer or sample handling, and no addition of chemicals or reagents. Hence the risk of contamination is low. The time for complete analysis is less than 10 min per sample. The concentrations of TPM determined in metropolitan Toronto ranged from 3 to 91 pg m(-)(3) with standard deviations of <±2 pg m(-)(3) for simultaneous sets of four samples. These atmospheric TPM concentration values fall within the range reported in the literature. Good agreement was obtained by the three methods compared in a field study at Ny-?lesund (78°54'N, 11°53'E), Svalbard. The elevated values of TPM concentrations obtained using the method developed in this work may arise from the Arctic springtime conversion of atmospheric mercury from gas-phase to particulate-phase Hg species.