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.     

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.     

Speciation of Mercury in Microalgae by Isotope Dilution-inductively Coupled Plasma Mass Spectrometry

Species-specific stable isotope dilution in combination with gold trap- or gas chromatography (GC)-inductively coupled plasma mass spectrometry (ICP-MS) is reported for the determination of inorganic mercury and methylmercury in diatoms (Chaetoceros curvisetus). The optimum conditions for the separation parameters were established. The isotope dilution analysis was performed using ¹⁹⁹Hg-enriched Hg²⁺ and laboratory-synthesized ²⁰¹Hg-enriched methylmercury. The absolute detection limits obtained with isotope dilution-ICP-MS were 9 pg for total mercury and 0.6 pg for methylmercury. The relative error of 7 Hg isotopic abundances based on the peak area measurements was better than 2.0% for 20 pg of methylmercury (as Hg) and 250 pg of inorganic mercury. The accuracy of the method was validated with a biological certified reference material. The developed method was then applied to investigate the uptake of inorganic mercury and methylmercury by C. curvisetus. Continuous uptake of inorganic mercury and methylmercury was observed during 5 days of incubation.     

Speciation of Mercury in two Dimictic Lakes of North-East Germany During a Period of 600 Days

Abstract

The speciation of mercury was studied with respect to (a) dissolved atomic mercury, (b) dissolved ionic mercury, and (c) total mercury in two dimictic lakes of North-East Germany. Differential pulse anodic stripping voltammetry was used for the analyses. The results show that biological processes dominate the speciation. They are responsible for high concentrations of atomic mercury and also organomercury compounds. The oxidation of atomic mercury under environmental conditions in lake water is very slow, so that the equilibrium between Hg_aq° and Hg_aq and Hg_aq ²⁺ can only be established during long periods of decreased bioactivity, as in wintertime. The sedimentation of the detritus during summer leads to a very pronounced decrease of the overall mercury in the entire water body of the lakes.     

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.     

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.     

Determination of total and methyl mercury in human permanent healthy teeth by electrothermal atomic absorption spectrometry after extraction in organic phase

A simple and sensitive method has been developed for determination of inorganic and methyl mercury in biological samples by ETAAS. For determination of methyl mercury; it was transferred to toluene phase by acid leaching extraction method. For total mercury after digestion of samples; it was extracted to toluene phase by means of the chelating agent diethyldithiocarbamate. Formation of complex between MeHg and diethyldithiocarbamate enhance the MeHg signal and increases the reproducibility. Furthermore, Pd-DDC was used as modifier for both mercury and methyl mercury determinations. The optimization performance was independently carried out by modifying the parameters such as temperature of mineralization, atomization and gas flow rate for methylmercury and inorganic mercury in ETAAS. The limits of detection were 0.15 and 0.12 μg g⁻¹ for methyl mercury and total mercury, respectively. The repeatability of the measurements of whole procedure were 15.8% for methyl mercury and 16.9% for total mercury determination. The accuracy of the method has been investigated by means of spiking different amounts of methylmercury and inorganic mercury to the samples. The recoveries were found within the range of 88-95% for methyl mercury and 85-92% for total mercury. For determination of total mercury, the method was validated by CVAAS. The obtained results by the present procedure were in good agreement with those of the CVAAS. The proposed method was applied for 30 human permanent healthy teeth (without filling) which significant positive correlations were found among number of amalgam filling and total mercury and MeHg.     

Non-chromatographic speciation analysis of mercury by flow injection on-line preconcentration in combination with chemical vapor generation atomic fluorescence spectrometry

A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg–DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH₄ solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h^− 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l^− 1 for Hg²⁺ and 2.0 ng l^− 1 for CH₃Hg⁺. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l^− 1 of Hg²⁺ and CH₃Hg⁺ were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.     

Short-term bioconcentration and distribution of methylmercury,tributyltin and corresponding inorganic species in the starfish leptasterias polaris

Starfish, Leptasterias polaris, were exposed between 30 min and 48 h to seawater containing 0.25 nmol dm^?3 of radiolabelled methylmercury (Me²⁰³HgCI), tributyltin [(C₄H₉)₃¹¹³SnCI], and inorganic ²⁰³HgCI₂ and ¹¹³SnCI⁴, with the objectives of comparing the uptake and distribution kinetics of these metal species in organs and tissues of treated organisms. Some starfish exposed to metals for 48 h were allowed to depurate for 24 h in clean seawater. Whole-body autoradiography was used to locate radiotracers very precisely within starfish tissues. The total amount of methylmercury (MeHg) accumulated in the whole animal after 48 h reached 0.53 nmol compared with 0.09 nmol for inorganic mercury, while tributyltin (TBT) reached 0.72 nmol compared with 0.017 nmol for inorganic tin. No significant reduction of body burdens occurred during the depuration period. The first-order rate constant characterizing the uptake of metals by whole animals, k₁, ranged from 0.102 h^?1 for MeHg to 3.6 × 10^?3h^?1 for inorganic mercury(II) and to 8.4 × 10^?4 h^?1 for inorganic tin(IV). The first-order rate constant characterizing the translocation of metals from seawater-exposed tissues toward internal organs, k₃, was available for inorganic Hg and Sn and had values similar to k₁. Concentration ratios between external tissues and internal organs after a 48 h exposure were 11.5 and 25.4 for MeHg and TBT, respectively, and 2.1 and 6.1 for inorganic mercury and tin. Furthermore, autoradiograms showed that MeHg and TBT were accumulated only on the external surface of the body wall and podia. This finding indicates a much slower translocation process for organometallic species than inorganic species, a process which seems to be related to the binding mode of MeHg and TBT to the organic matrix of external tissues of starfish.     

Re‐evaluation of distillation and comparison with HNO3 leaching/solvent extraction for isolation of methylmercury compounds from sediment/soil samples

Distillation was re‐evaluated for the formation of artifacts arising from increasing naturally occurring mercury(II) concentrations, as opposed to previous identification of artifacts by spiking standard mercury(II) into samples. Naturally occurring mercury(II) concentrations lower than 2 µg g^?1 were found not to affect methylmercury (MeHg) results. However, when the natural concentrations of mercury(II) were greater than 2 µg g^?1, in contrast to standard mercury(II) spiked in samples, the MeHg concentrations measured were found to decrease (not increase) with increasing naturally occurring mercury(II) concentrations. This indicated that standard mercury(II) spiked in samples behaved differently from naturally occurring mercury(II) in the formation of MeHg artifacts during distillation. As a result, spiking standard mercury(II) into samples to identify the formation of MeHg artifacts is not adequate. It is difficult to explain why high naturally occurring mercury(II) suppresses MeHg measurements during distillation. In comparison with HNO₃ leaching/solvent extraction (and other existing techniques), distillation was found to generate results comparable for samples containing less than 2 µg g^?1 mercury(II). The HNO₃ leaching/solvent extraction showed significant advantages over other procedures, as this technique generated the highest recoveries with good precision for all samples analyzed, and the results were found to be independent of mercury(II) concentrations for both naturally occurring and spiked standard mercury(II). Thus, except for samples from high mercury‐contaminated fields, distillation is still a good choice. Both the positive bias (possibly caused by artifact formation of MeHg) and the negative bias (due to incomplete leaching, back‐adsorption, and/or decomposition of MeHg) were investigated. Geologically, physically, and chemically different samples were used for the investigation. Copyright © 2004 John Wiley & Sons, Ltd.     

Development of a novel and robust microprecipitation approach using cetyltrimethyl ammonium bromide (CTAB) for preconcentration and speciation of mercury in waters prior to CVAAS determination

A novel and simple microprecipitation method was developed for the preconcentration of ultra-trace quantities of inorganic and methyl mercury species (iHg and MeHg) prior to their determination by cold vapour atomic absorption spectrometry (CVAAS). This method is based on the formation of anionic complexes of Hg²⁺ with KI followed by ion-associate complex with cetyltrimethyl ammonium bromide (CTAB) that forms a fluffy precipitate in perchloric acid medium. As a result, a fluffy coagulated mass separates and collects at the top of the liquid surface with clear phase separation without need of cooling or heating or centrifugation. The ion-association complex of iHg was then extracted into surfactant-rich phase (top layer) of CTAB-perchlorate precipitate while the uncomplexed MeHg remained in the aqueous phase (bottom layer). This condition also facilitates the removal of aqueous phase by simply draining out. The fluffy mass formed was dissolved in a mixture of HNO₃ and HCl which was subsequently treated with chloroform to separate the surfactant from the mixture. Then the aqueous phase containing the preconcentrated iHg was analysed for mercury by CVAAS. Key factors such as sample pH, concentration of KI and CTAB that affect the performance of the proposed microprecipitation method were thoroughly investigated. For the determination of total mercury, another fresh aliquot of water was initially adjusted to pH ~ 3.5 with perchloric acid and subjected to oxidation by using modified UV-irradiation set-up and then taken through the microprecipitation procedure. This method allows speciation of mercury with a preconcentration factor of 200 and the limits of detection (LOD) of mercury obtained for CVAAS in conjunction with the present preconcentration method was found to be 2.4 ng L^?1. Average recoveries obtained with the proposed approach were found to be in the range of 96–104% with RSD values < 5%. The interfering effects of various cations and anions were also investigated. The method was successfully applied for the determination of ultra-trace quantities of mercury species in real samples such as bottled water, tap water, lake water and ground waters.     

Mercury speciation in thawed out and refrozen fish samples by gas chromatography coupled to inductively coupled plasma mass spectrometry and atomic fluorescence spectroscopy

Different sub-sampling procedures were applied for the determination of mercury species (as total mercury Hg, methylmercury MeHg⁺ and inorganic mercury Hg²⁺) in frozen fish meat. Analyses were carried out by two different techniques. After the sample material was pre-treated by microwave digestion, atomic fluorescence spectroscopy (AFS) was used for the determination of total Hg. Speciation analysis was performed according to the following procedure: dissolution of sample material in tetramethylammonium hydroxide (TMAH), derivatisation with sodium tetraethylborate (NaBEt₄), extraction into isooctane and measurement with gas chromatography inductively coupled plasma mass spectrometry (GC-ICPMS) for the identification and quantification of methylmercury (MeHg⁺) and inorganic mercury (Hg²⁺). The concentration range of total Hg measured in the shark fillets is between 0.9 and 3.6 g g^–1 thawed out shark fillet. Speciation analysis leads to 94% Hg present as MeHg⁺. Homogeneity, storage conditions and stability of analytical species and sample materials have great influence on analytical results. Sub-sampling of half-frozen/partly thawed out fish and analysis lead to significantly different concentrations, which are on average a factor of two lower.     

CaCl2添加对热解煤中汞析出规律影响的实验研究

在程序升温热解反应装置上,研究了低氯煤中添加不同氯含量（质量分数0.1%、0.3%、0.5%）的CaCl₂对煤热解过程中汞析出规律的影响。实验结果表明,温度是影响汞析出的关键因素;随着氯添加量的增加,Hg²⁺析出比例呈上升趋势,且汞的最佳析出温度降低,汞的释放率也有所降低;随着热解气氛中O₂比例的增加,Hg²⁺比例也略有增加;较高的升温速率能加快汞的释放,也能提高Hg²⁺的比例。低氯煤中添加氯化钙能够强化单质汞的氧化。     

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.     

A methodological study of mercury speciation using Dogfish liver CRM (DOLT-2)

The purpose of the study was to optimise analytical methods for determination of the chemical speciation of mercury in studies of protective mechanisms of selenium. Optimisation of the methods was performed using CRM DOLT-2 (Dogfish liver), both in its original form and after separation of various fractions. The sample was homogenised with 10 mM Tris-HCl buffer (pH 7.6) and ultracentrifuged. The soluble phase obtained was applied to a size exclusion chromatography column (Sephadex ¶G-75 column) for separation of various protein fractions. Total mercury (total Hg), monomethyl mercury (MeHg) and selenium (Se) were determined in whole dogfish liver tissue and its soluble and insoluble phases (pellet). Different approaches for determination of total Hg and MeHg were compared. Simultaneous determination of MeHg and inorganic mercury (Hg²⁺) was based on alkaline dissolution and/or acid leaching, followed by ethylation, room temperature precollection, isothermal gas chromatography (GC), pyrolysis and detection with cold vapour atomic fluorescence spectrometry (CVAFS). The sum of MeHg and Hg²⁺ was compared to total Hg results obtained by acid digestion and CVAAS detection. The accuracy of MeHg determination was checked by its determination using acid leaching at room temperature, solvent extraction, back extraction into Milli-Q water, ethylation, GC and CVAFS detection. For the insoluble phase it is recommended to use solvent extraction for MeHg and acid digestion CVAAS for total Hg. For determination of MeHg and Hg²⁺ in the lyophilised sample and water soluble fractions containing low concentrations of mercury species, the simultaneous measurement of MeHg and Hg²⁺ after alkaline dissolution is the most appropriate method.     

Non-chromatographic screening method for the determination of mercury species. Application to the monitoring of mercury levels in Antarctic samples

A simple non-chromatographic method for the determination of mercury (Hg²⁺), methylmercury (MeHg⁺), dimethylmercury (Me₂Hg), and phenylmercury (PhHg⁺) employing atomic fluorescence spectrometry (AFS) as detection technique was developed. Mercury species showed a particular behavior in the presence of several reagents. In a first stage SnCl₂ was employed for Hg²⁺ determination; in a second step, [Hg²⁺ + PhHg⁺] concentration was determined using SnCl₂ and UV radiation. MeHg⁺ decomposition was prevented adding 2-mercaptoethanol. In a third stage, [Hg²⁺ + PhHg⁺ + MeHg⁺] concentration was determined using K₂S₂O₈. Finally, the four species were determined employing NaBH₄. Reagents concentration and flow rates were optimized. The extraction technique of mercury species involved the use of 2-mercaptoethanol as ion-pair reagent. The limits of detection for Hg²⁺, PhHg⁺, MeHg⁺, and Me₂Hg were 1, 40, 68, and 99 ng L⁻¹ with a relative standard deviation of 1.5, 3.1, 4.7 and 5.8%, respectively. Calibration curve was linear with a correlation factor equal to 0.9995. The method was successfully applied to the determination of the mercury species in two Antarctic materials: IRMM 813 (Adamussium colbecki) and MURST-ISS-A2 (Antarctic Krill).     

Concentration levels of total and methylmercury in mussel samples collected along the coasts of Sardinia Island (Italy)

This paper reports the assessment of the total mercury (T-Hg) and methylmercury (MeHg) contamination of mussel samples collected by two sampling campaigns from along the coastline of Sardinia (Italy). T-Hg has been determined by a direct mercury analyser (DMA) whereas MeHg has been determined by gas chromatography-mass spectrometry (GC-MS) after acid extraction, and employs a novel NaBPh₄ derivatization method. The evaluation of the quality of measurements was carried out by analysing candidate certified reference material (CRM) BCR 710, for MeHg and T-Hg, and CRM IAEA-350 for T-Hg. In the analysed samples, the T-Hg concentrations range from 35 to 115 μg kg⁻¹ and from 40 to 830 μg kg⁻¹, for the two sampling campaigns, respectively, whereas the MeHg concentrations range from l5 to 51 μg kg⁻¹ and from 17 to 116 μg kg⁻¹. Consequently, the MeHg/T-Hg ratios range from 0.33 to 0.91 and from 0.14 to 0.98, respectively. Despite the increasing trend of Hg concentration from the first to the second sampling campaign, the T-Hg concentration of all the samples was much below the 0.5 μg g⁻¹ WHO limit, and the MeHg values ranged between 2.2 and 17.2 μg kg⁻¹, not exceeding the 43.5 μg kg⁻¹ tolerable daily residue level calculated for Italy.     

Measurement techniques for mercury species in ambient air

This review critically evaluates the measurement methodologies most commonly employed for the analysis of the various forms of mercury (Hg) in air. Emphasis is given to the three most common forms of mercury in air [i.e. gaseous elemental mercury (GEM, Hg⁰), reactive gaseous mercury (RGM), and particle-bound mercury (Hg_p)]. Moreover, we also briefly describe methods dealing with gas-phase analysis of organic mercury species (e.g., mostly methyl mercury), as they are also reported to be present in air on rare occasions. To begin with, we describe the approaches to sampling airborne mercury species and associated sample-treatment strategies. We evaluate both conventional and emerging alternative detection techniques for different mercury forms with respect to their applicability in airborne mercury analysis. We also discuss the artifacts and the biases associated with analysis of different mercury species. Finally, the review summarizes current methodological developments for the determination of mercury in air and highlights future prospects for improvements.     

Enzymatic Determination of Methylmercury Traces using Alcohol Dehydrogenase from Baker’s Yeast

 Methylmercury as well as mercury (II) were found to be effective inhibitors of the catalytic activity of alcohol dehydrogenase from baker’s yeast in the reaction of ethanol oxidation by nicotinamide adenine dinucleotide. It was stated that the methylmercury inhibitory action belonged to the non-competitive type, whereas Hg(II) inhibited the enzyme according to the mixed type. The inversely proportional dependence of the indicator reaction rate on the concentration of methylmercury allowed to develop an enzymatic procedure for its determination with a detection limit of 3 nM. The possibility of methylmercury determination in presence of mercury (II) and mercury (II) determination in presence of methylmercury (concentration ratios CH₃Hg⁺:Hg(II) were 1:1 and 1:10, respectively) was shown. In the first case masking reagents, DEDTC or thiourea, were used to form stable complexes with Hg(II). Received February 9, 2001; accepted August 10, 2001; published online June 24, 2002