Simultaneous determination of methyl- and ethyl-mercury by solid-phase microextraction followed by gas chromatography atomic fluorescence detection

A method for trace level determination of organomercury species in different biota matrixes by using aqueous-phase propylation followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography (GC) coupled to pyrolysis-atomic fluorescence spectrometry (Py-AFS) detection has been optimized. To maximize peak area and symmetry factors of methylmercury (MeHg) and ethylmercury (EtHg) analyzed as propyl derivatives, carrier and make-up flow rates were optimized by a user-defined experimental design. A multiple response simultaneous optimization was applied using the desirability function to achieve global optimal operating conditions. They were attained at 2 and 6 mL min⁻¹ as carrier and make-up gas flow rates, respectively. In addition, pyrolyser temperature was also optimized, yielding the best value at 750 °C. Limits of detection and quantification at the optimum conditions were 0.04 ng g⁻¹ and 0.13 ng g⁻¹ for both, MeHg and EtHg. The developed analytical procedure was validated with a certified reference material (DORM-2) and applied to the determination of organomercury incurred in waterfowl egg and fish samples.     

Speciation analysis of mercury by dispersive solid‐phase extraction coupled with capillary electrophoresis

A pretreatment method of dispersive solid‐phase extraction (DSPE) along with back‐extraction followed by CE‐UV detector was developed for the determination of mercury species in water samples. Sulfhydryl‐functionalized SiO₂ microspheres (SiO₂−SH) were synthesized and used as DSPE adsorbents for selective extraction and enrichment of three organic mercury species namely ethylmercury (EtHg), methylmercury (MeHg), and phenylmercury (PhHg), along with L‐cysteine (L‐cys) containing hydrochloric acid as back‐extraction solvent. Several main extraction parameters were systematically investigated including sample pH, amount of adsorbent, extraction and back‐extraction time, volume of eluent, and concentration of hydrochloric acid. Under optimal conditions, good linearity was achieved with correlation coefficients over 0.9990, in the range of 4−200 μg/L for EtHg, and 2−200 μg/L for MeHg and PhHg. The LODs were obtained of 1.07, 0.34, and 0.24 μg/L for EtHg, MeHg, and PhHg, respectively, as well as the LOQs were 3.57, 1.13, and 0.79 μg/L, respectively, with enrichment factors ranging from 109 to 184. Recoveries were attained with tap and lake water samples in a range of 62.3−107.2%, with relative standard deviations of 3.5–10.1%. The results proved that the method of SiO₂−SH based DSPE coupled with CE‐UV was a simple, rapid, cost‐effective, and eco‐friendly alternative for the determination of mercury species in water samples.     

Determination of the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human hair by solid-phase extraction and gas chromatography-mass spectrometry

Summary A method for the determination of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human hair has been developed and validated. Hair samples (200 mg) were dissolved in NaOH (1 M) and PhIP was isolated by successive solid-phase extraction on a polystyrene-divinylbenzene column and on a silica-based mixed-mode column with C₈ and-SO₃ ⁻ functional groups. Quantification was performed by gas chromatography-electron-impact ionization high-resolution mass spectrometry in selected-ion-monitoring mode. The method was validated for determination of PhIP in the concentration range 0.5–25 ng g⁻¹ hair with [²H₃]PhIP as internal standard. The limit of quantification was 0.26 ng g⁻¹ hair. Within-day and between-day precision were in the ranges 1–27% and 2–15% relative standard deviation, respectively. The hair sample used for method validation was found to contain 0.26 ng PhIP g⁻¹ hair.     

Methylmercury determination in biological samples using electrothermal atomic absorption spectrometry after acid leaching extraction

An efficient and sensitive method for the determination of methylmercury in biological samples was developed based on acid leaching extraction of methylmercury into toluene. Methylmercury in the organic phase was determined by electrothermal atomic absorption spectrometry (ETAAS). The methylmercury signal was enhanced and the reproducibility increased by formation of certain complexes and addition of Pd-DDC modifier. The complex of methylmercury with DDC produced the optimum analytical signal in terms of sensitivity and reproducibility compared to complexes with dithizone, cysteine, 1,10-phenanthroline, and diethyldithiocarbamate. Method performance was optimized by modifying parameters such as temperature of mineralization, atomization, and gas flow rate. The limit of detection for methylmercury determination was 0.015 μg g⁻¹ and the RSD of the whole procedure was 12% for human teeth samples (n=5) and 15.8% for hair samples (n=5). The method’s accuracy was investigated by using NIES-13 and by spiking the samples with different amounts of methylmercury. The results were in good agreement with the certified values and the recoveries were 88–95%.     

Simultaneous multi-species determination of trimethyllead,monomethylmercury and three butyltin compounds by species-specific isotope dilution GC–ICP–MS in biological samples

An accurate and sensitive multi-species species-specific isotope dilution GC–ICP–MS method was developed for the simultaneous determination of trimethyllead (Me₃Pb⁺), monomethylmercury (MeHg⁺) and the three butyltin species Bu₃Sn⁺, Bu₂Sn²⁺, and BuSn³⁺ in biological samples. The method was validated by three biological reference materials (CRM 477, mussel tissue certified for butyltins; CRM 463, tuna fish certified for MeHg⁺; DORM 2, dogfish muscle certified for MeHg⁺). Under certain conditions, and with minor modifications of the sample pretreatment procedure, this method could also be transferred to environmental samples such as sediments, as demonstrated by analyzing sediment reference material BCR 646 (freshwater sediment, certified for butyltins). The detection limits of the multi-species GC–ICP–IDMS method for biological samples were 1.4 ng g⁻¹ for MeHg⁺, 0.06 ng g⁻¹ for Me₃Pb⁺, 0.3 ng g⁻¹ for BuSn³⁺ and Bu₃Sn⁺, and 1.2 ng g⁻¹ for Bu₂Sn²⁺. Because of the high relevance of these heavy metal alkyl species to the quality assurance of seafood, the method was also applied to corresponding samples purchased from a supermarket. The methylated lead fraction in these samples, correlated to total lead, varied over a broad range (from 0.01% to 7.6%). On the other hand, the MeHg⁺ fraction was much higher, normally in the range of 80–100%. Considering that we may expect tighter legislative limitations on MeHg⁺ levels in seafood in the future, we found the highest methylmercury contents (up to 10.6 μg g⁻¹) in two shark samples, an animal which is at the end of the marine food chain, whereas MeHg⁺ contents of less than 0.2 μg g⁻¹ were found in most other seafood samples; these results correlate with the idea that MeHg⁺ is usually of biological origin in the marine environment. The concentration of butyltins and the fraction of the total tin content that is from butyltins strongly depend on possible contamination, due to the exclusively anthropogenic character of these compounds. A broad variation in the butylated tin fraction (in the range of <0.3–49%) was therefore observed in different seafood samples. Corresponding isotope-labeled spike compounds (except for trimethyllead) are commercially available for all of these compounds, and since these can be used in the multi-species species-specific GC-ICP-IDMS method developed here, this technique shows great potential for routine analysis in the future.     

Simultaneous determination of methylmercury and ethylmercury in rice by capillary gas chromatography coupled on-line with atomic fluorescence spectrometry

A comprehensive method for simultaneous determination of methylmercury (MeHg) and ethylmercury (EtHg) in rice by capillary gas chromatography (GC) coupled on-line with atomic fluorescence spectrometry was developed. The experimental conditions, including the pyrolyzer temperature and flow rates of the make-up gas and sheath gas, were optimized in detail. The absolute detection limits (3sigma) were 0.005 ng as Hg for both MeHg and EtHg. The relative standard deviation values (n=5) for 10 ng Hg/mL of MeHg and EtHg were 2.5 and 1.3%, respectively. The method was evaluated by analyzing 2 certified reference materials (DORM-2 and GBW08508), and the determined values of MeHg and total mercury concentrations were in good agreement with the certified values. In addition, the recoveries of MeHg and EtHg spiked into a rice sample collected from Jiangsu province in China were 86 and 77%, respectively. The proposed method was applied to analysis of MeHg and EtHg in 25 rice samples cultivated in 15 provinces of China. In all samples, MeHg was detectable and no EtHg was found. The MeHg contents in rice samples ranged from 1.9 to 10.5 ng/g, accounting for 7-44% of the total mercury measured.     

Investigation of the species-specific degradation behaviour of methylmercury and ethylmercury under microwave irradiation

The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh₄). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min. The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte loss was observed for EtHg after 2 minutes at 40 W of microwave power. Awarded a Poster Prize on the occasion of the European Winter Conference on Plasma Spectrochemistry, February 2005, Budapest, Hungary     

Speciation of organomercury compounds by capillary electrophoresis with pre-column derivatization and on-line stacking

A simple capillary electrophoresis method was developed to separate and quantify methylmercury, ethylmercury, and phenylmercury with the enhancement of pre-column derivatization and on-line stacking.     

汞的形态分析研究 Ⅱ.固相萃取预富集-液相色谱分离测定不同形态的有机汞

本文报道了固相萃取预富集处理样品继以液相色谱分离测定不同形态痕量有机汞的方法.二乙基二硫代氨基甲酸钠(DDTC)作络合剂及甲醇作洗脱液的预富集系统能在线富集甲基汞(MeHg)、乙基汞(EtHg)和苯基汞(PhHg).用于测定加标海水中MeHg、EtHg和PhHg,回收率分别为96.9％、102.4％和98.0％;相对标准偏差分别为3.5％、5.0％和5.0％;检测下限分别为 1.0μg/L、1.2 μg/L和 1.2 μg/L.     

Determination of <Superscript>90</Superscript>Sr in contaminated environmental samples by tuneable bandpass dynamic reaction cell ICP–MS

A rapid method for the extraction and determination of ⁹⁰Sr in natural water, plant and sediment samples was developed using extraction chromatography and dynamic reaction cell ICP–MS, with O₂ as a reaction gas. While isobaric interference from the stable isotope ⁹⁰Zr was efficiently removed by this method, interferences produced from in-cell reactions with Fe⁺ and Ni⁺ required suppression by tuneable bandpass, and in sediments, additional chromatographic separation. Method detection limits were 0.1 pg g⁻¹ (0.5 Bq g⁻¹), 0.04 pg g⁻¹(0.2 Bq g⁻¹), and 3 pg L⁻¹ (5 Bq L⁻¹) for sediments, plant and water samples, respectively, and ⁹⁰Sr concentrations determined by ICP–MS were in good agreement with activities determined by Cerenkov counting and with certified reference values. While mass spectrometric determination does not rival detection limits achievable by radiometric counting, radiometric determination of ⁹⁰Sr, a pure beta-emitter, is hindered by long analysis times (several weeks); the comparatively fast analysis achieved via ICP–MS enables same-day preparation and analysis of samples, making this an important technique for the environmental monitoring of areas contaminated by radioactivity.     

Mercury speciation by coupling cold vapour atomic absorption spectrometry with flow injection on-line preconcentration and liquid chromatographic separation

A fully automated system for the direct determination of methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) at the ng/L level is described. It is based on solid phase extraction preconcentration incorporated in a flow injection (FI) system, high performance liquid chromatography (HPLC) separation, reduction combined with thermolysis and determination by cold vapour atomic absorption spectrometry (CVAAS). For preconcentration a microcolumn of bonded silica with octadecyl functional groups (C18 reversed phase material) was used as a sorbent for the mercury complexes formed on-line with ammonium pyrrolidine dithiocarbamate. Retained mercury species are eluted with a methanol-acetonitrile-water mixture and subjected to separation on an octadecylsilane (ODS) column before determination by CVAAS. The sensitivity of organo-mercury determination could be improved by using NaBH₄ as a reductant combined with a thermolysis step. In order to perform on-line measurements the preconcentration microcolumn was mounted in a pressure-tight casing. Limits of detection for MeHg, EtHg, PhHg and Hg(II) employing a sample volume of 58.5 mL were 9, 6, 10 and 5 ng/L, respectively. The relative standard deviation (RSD) calculated from 9 repeated measurements was found to be 3.6%, 5.5%, 10.4% and 7.6% for MeHg, EtHg, PhHg and Hg(II), respectively. Finally, the application of this method for speciation of mercury in fish and human urine is described.     

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.     

Comparative study of inorganic elements determination in whole blood from Crioula breed horse by EDXRF and NAA analytical techniques

The World Health Organization states that envenomation is responsible for a high number of deaths per year, especially in equatorial areas. The only effective specific treatment is the use of hyperimmune serum (antivenom). In Brazil, Crioula breed horses are used for antivenom production, with great importance in the maintenance of public health programs. A strict biochemical and metabolic control is required to attain specificity in antiserum. Inorganic elements represent only a small fraction of whole blood. Nonetheless, they play important roles in mammalian metabolism, being responsible for controlling enzymatic reactions, respiratory and cardiac functions and ageing. In this work, whole blood samples from Crioula breed horses were analyzed by EDXRF technique. The reference interval values were determined for the elements Na (1955–2013 μg g⁻¹), Mg (51–75 μg g⁻¹), P (523–555 μg g⁻¹), S (1628–1730 μg g⁻¹), Cl (2388–2574 μg g⁻¹), K (1649–1852 μg g⁻¹), Ca (202–213 μg g⁻¹), Cu (4.1–4.5 μg g⁻¹) and Zn (2.4–2.8 μg g⁻¹) and a comparative study with NAA results was outlined. The samples were obtained from Instituto Butantan. Both techniques showed to be appropriate for whole blood sample analyses and offer a new perspective in Veterinary Medicine.     

Determination of methyl- and ethylmercury in natural waters at sub-nanogram per liter using SCF-adsorbent preconcentration procedure

An analytical procedure for determining methyl- and ethylmercury (MeHg/EtHg) in natural waters is described. MeHg/EtHg was preconcentrated from water on a sulfhydryl cotton fiber (SCF) adsorbent and eluted with a small volume of a mixture of 1 M hydrochloric acid and 2 M sodium chloride. The eluate was extracted with benzene. The measurements of MeHg/EtHg in benzene extract were determined by gas chromatography with electron capture detector. The detection limit for MeHg/EtHg was about 0.04 ng L-1 using a 20 L water sample. The precision was about 20%. The application of the proposed method to one snow and four freshwater samples varying in humus content is described. The MeHg concentrations found in different freshwater samples were ranged from 0.09 to 0.22 ng L-1 and the recoveries of spiked MeHg were ranged from 42 to 68% which were strongly correlated to the content of humic substances. The MeHg concentration found in snow was 0.28 ng L-1 and the recovery was 79%. The analytical results of MeHg concentration in freshwater samples are discussed in relation to the pH used in the preconcentration, the humus content, the fraction of methylmercury in organic bound mercury and mercury in fish.     

Mercury speciation by coupling cold vapour atomic absorption spectrometry with flow injection on-line preconcentration and liquid chromatographic separation

A fully automated system for the direct determination of methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) at the ng/L level is described. It is based on solid phase extraction preconcentration incorporated in a flow injection (FI) system, high performance liquid chromatography (HPLC) separation, reduction combined with thermolysis and determination by cold vapour atomic absorption spectrometry (CVAAS). For preconcentration a microcolumn of bonded silica with octadecyl functional groups (C18 reversed phase material) was used as a sorbent for the mercury complexes formed on-line with ammonium pyrrolidine dithiocarbamate. Retained mercury species are eluted with a methanol-acetonitrile-water mixture and subjected to separation on an octadecylsilane (ODS) column before determination by CVAAS. The sensitivity of organo-mercury determination could be improved by using NaBH₄ as a reductant combined with a thermolysis step. In order to perform on-line measurements the preconcentration microcolumn was mounted in a pressure-tight casing. Limits of detection for MeHg, EtHg, PhHg and Hg(II) employing a sample volume of 58.5 mL were 9, 6, 10 and 5 ng/L, respectively. The relative standard deviation (RSD) calculated from 9 repeated measurements was found to be 3.6%, 5.5%, 10.4% and 7.6% for MeHg, EtHg, PhHg and Hg(II), respectively. Finally, the application of this method for speciation of mercury in fish and human urine is described. Received: 10 March 1997 / Revised: 29 January 1998 / Accepted: 5 February 1998     

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     

Synthesis and supercapacitance of flower-like Co(OH)<Subscript>2</Subscript> hierarchical superstructures self-assembled by mesoporous nanobelts

A facile hydrothermal strategy was first proposed to synthesize flower-like Co(OH)₂ hierarchical microspheres. Further physical characterizations revealed that the flower-like Co(OH)₂ microspherical superstructures were self-assembled by one-dimension nanobelts with rich mesopores. Electrochemical performance of the flower-like Co(OH)₂ hierarchical superstructures were investigated by cyclic voltammgoram, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 3 M KOH aqueous electrolyte. Electrochemical data indicated that the flower-like Co(OH)₂ superstructures delivered a specific capacitance of 434 F g⁻¹ at 10 mA cm⁻² (about 1.33 A g⁻¹), and even kept it as high as 365 F g⁻¹ at about 5.33 A g⁻¹. Furthermore, the SC degradation of about 8% after 1,500 continuous charge–discharge cycles at 5.33 A g⁻¹ demonstrates their good electrochemical stability at large current densities.     

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.     

Determination of heterocyclic aromatic amines (HAA) in commercially available meat products and fish by high performance liquid chromatography—Electrospray tandem mass spectrometry (HPLC-ESI-MS-MS)

Summary Ten heterocyclic aromatic amines (HAA) (1)–(10) were analyzed in commercially available meat products and fish. After sample preparation by Extrelut treatment and subsequent solid phase extraction applying propylsulphonic and C₁₈ silica cartridges, HPLC-ESI-MS-MS using selected reaction monitoring (SRM) and d₃-PhIP and d₃-MeIQx as internal and external standards, respectively, revealed the widely distributed presence of PhIP (8) and MeIQx (4), ranging from 0.1 to 5.3 ng g⁻¹ and 0.1 to 5.2 ng g⁻¹, respectively. Lower amounts were found for 4,8-DiMeIQx (5) and 7,8-DiMeIQx (6), ranging from 0.2 to 2.0 ng g⁻¹ and 0.1 to 0.2 ng g⁻¹, respectively. The other HAA under study, i.e. IQ, MeIQ, 4,7,8-TriMeIQx, Glu-P-1, and Glu-P-2 were not determinable under the experimental conditions used (determination limit 0.1 ng g⁻¹).     

Spectrofluorimetric determination of trace amounts of coenzyme A using a terbium ion–ciprofloxacin complex probe in the presence of periodic acid

A new spectrofluorimetric method was developed for the determination of trace amounts of coenzyme A (CoA). In the presence of periodic acid (H₅IO₆), CoA can remarkably enhance the fluorescence intensity of the Tb³⁺–ciprofloxacin (CIP) complex at 545 nm in a buffer solution at pH 5.4; the enhanced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of CoA. The optimal conditions for the determination of CoA were also investigated. The linear range and the detection limit for the determination of CoA were 6.08 × 10⁻⁶–1.64 × 10⁻⁵ and 2.1 × 10⁻⁸ mol L⁻¹, respectively. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess CoA in injection and biological samples. Moreover, the enhancement mechanism of the fluorescence intensity of the CoA–Tb³⁺–CIP system in the presence of H₅IO₆ is also discussed.