Analysis of organomercury compounds in sediments by capillary GC with atomic fluorescence detection

Analysis of methyl- and ethylmercury (MM and EM) halides in biological and environmental samples is generally performed by gas chromatography with electron capture detection. Tedious sample work-up protocols and poor chromatographic response (using packed columns) have, however, shown the need for the development of new methods in this field. This paper reports a sensitive method, free from these deficiencies, for the determination of methyl- and ethylmercury. The organomercury compounds (MM and EM) are first released from the sample matrix, by the combined action of acidic potassium bromide and cupric ions, and then extracted into dichloromethane. The initial extracts are subjected to thiosulfate clean-up and the organomercury species are isolated as their chloride derivatives by addition of cupric chloride, and subsequent extraction into a small volume of organic solvent. Capillary GC coupled with atomic fluorescence detection provided excellent separation efficiencies for methyl- and ethylmercury and proved to be a very selective and sensitive technique. The absolute detection limit for both MM and EM was found to be 0.2 pg.     

Mercury speciation in sea food by flow injection cold vapor atomic absorption spectrometry using selective solid phase extraction

An on-line inorganic and organomercury species separation, preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS or CV-ETAAS) coupled to a flow injection (FI) method was studied. The inorganic mercury species was retained on a column (i.d., 3 mm; length 3 cm) packed to a height of 0.7 cm with a chelating resin aminopropyl-controlled pore glass (550 A) functionalized with [1,5-bis (2 pyridyl)-3-sulphophenyl methylene thiocarbonohydrazyde] placed in the injection valve of a simple flow manifold. Methylmercury is not directly determined. Previous oxidation of the organomercurial species permitted the determination of total mercury. The separation of mercury species was obtained by the selective retention of inorganic mercury on the chelating resin. The difference between total and inorganic mercury determined the organomercury content in the sample. The inorganic mercury was removed on-line from the microcolumn with 6% (m/v) thiourea. The mercury cold vapor generation was performed on-line with 0.2% (m/v) sodium tethrahydroborate and 0.05% (m/v) sodium hydroxide as reducing solution. The determination was performed using CV-AAS and CV-ETAAS, both approaches have been used and compared for the speciation of mercury in sea food. A detection limit of 10 and 6 ng l(-1) was achieved for CV-AAS and CV-ETAAS, respectively. The precision for 10 replicate determinations at the 1 microg l(-1) Hg level was 3.5% relative standard deviation (R.S.D.), calculated from the peak heights obtained. Both approaches were validated with the use of two certified reference materials and by spiking experiments. By analyzing the two biological certified materials, it was evident that the difference between the total mercury and inorganic mercury corresponds to methylmercury. The concentrations obtained by both techniques were in agreement with the certified values or with differences of the certified values for total Hg(2+) and CH(3)Hg(+), according to the t-test for a 95% confidence level. It is amazing how this very simple method is able to provide very important information on mercury speciation.     

Indirect Mercury Speciation in Biological Tissues by Closed‐Vessel Microwave‐Assisted Digestion and Flow‐Injection Cold‐Vapor Atomic Fluorescence Detection

Abstract

A simple and rapid method based on closed vessel microwave‐assisted extraction was developed to determine total, inorganic mercury and organomercury in biological tissues. Total mercury was extracted using HNO₃:H₂O₂ (4:1) mixture. In a separate subsample, extraction of mercury species was carried out with tetramethylammonium hydroxide (TMAH). The total and inorganic mercury analyses were carried out by flow‐injection cold‐vapor atomic fluorescence spectrometry (FI‐CV‐AFS). The organomercury concentration was calculated by difference. Considering a sample amount of 0.2 g, the detection limits were 4 and 26 ng/g for total and inorganic mercury, respectively. The accuracy of the procedures was checked by analyzing certified reference materials and recovery studies of spiked fish tissues.     

Simple method of determination of copper,mercury and lead in potable water with preliminary pre-concentration by total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence spectrometry and chemical pre-concentration procedures have been applied for the analysis of trace concentrations of copper, mercury, and lead in drinking water samples. A simple total reflection module has been used in X-ray measurements. The elements under investigation were pre-concentrated by complexation using a mixture of carbamates followed by solvent extraction with methyl isobutyl ketone. The preconcentration procedure was tested with the use of twice-distilled water samples and samples of mineral and tap water spiked with known additions of copper, mercury, and lead. The obtained recovery and precision values are presented. The minimum detection limits for the determination of these elements in mineral and tap water samples were found to be 40 ng l⁻¹, 60 ng l⁻¹, and 60 ng l⁻¹, respectively.     

冷蒸气发生-原子荧光光谱法测定化工废水中的无机汞和总有机汞

用氢化物发生－原子荧光光谱法测定了化工废水中的无机汞和总有机汞。无机汞可以直接测定;用过硫酸钾在沸水浴中加热20min即可把有机汞转化为无机汞,实现总汞的测定,二者之差为总有机汞。对影响测定灵敏度的一些实验参数进行了优化,汞的检测限为8．2ng/L。     

Comparison of gas chromatographic hyphenated techniques for mercury speciation analysis

In this study, we evaluate advantages and disadvantages of three hyphenated techniques for mercury speciation analysis in different sample matrices using gas chromatography (GC) with mass spectrometry (GC-MS), inductively coupled plasma mass spectrometry (GC-ICP-MS) and pyrolysis atomic fluorescence (GC-pyro-AFS) detection. Aqueous ethylation with NaBEt(4) was required in all cases. All systems were validated with respect to precision, with repeatability and reproducibility <5% RSD, confirmed by the Snedecor F-test. All methods proved to be robust according to a Plackett-Burnham design for 7 factors and 15 experiments, and calculations were carried out using the procedures described by Youden and Steiner. In order to evaluate accuracy, certified reference materials (DORM-2 and DOLT-3) were analyzed after closed-vessel microwave extraction with tetramethylammonium hydroxide (TMAH). No statistically significant differences were found to the certified values (p=0.05). The suitability for water samples analysis with different organic matter and chloride contents was evaluated by recovery experiments in synthetic spiked waters. Absolute detection and quantification limits were in the range of 2-6 pg for GC-pyro-AFS, 1-4 pg for GC-MS, with 0.05-0.21 pg for GC-ICP-MS showing the best limits of detection for the three systems employed. However, all systems are sufficiently sensitive for mercury speciation in environmental samples, with GC-MS and GC-ICP-MS offering isotope analysis capabilities for the use of species-specific isotope dilution analysis, and GC-pyro-AFS being the most cost effective alternative.     

The use of emulsions for the determination of methylmercury and inorganic mercury in fish-eggs oil by cold vapor generation in a flow injection system with atomic absorption spectrometric detection

An on-line time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwave-aided oxidation with potassium persulfate has been developed for the determination of the different mercury species in fish-eggs oil samples. A three-phase surfactant-oil-water emulsion produced an advantageous flow when a peristaltic pump was used to introduce the highly viscous sample into the system. The optimum proportion of the oil-water mixture ratio was 2:3 v/v with a Tween 20 surfactant concentration in the emulsion of 0.008% v/v. Inorganic mercury was determined after reduction with sodium borohydride while total mercury was determined after an oxidation step with persulfate prior to the reduction step to elemental mercury with the same reducing agent. The difference between total and inorganic mercury determined the organomercury content in samples. A linear calibration graph was obtained in the range 0.1-20 micrograms l-1 of Hg2+ by injecting 0.7 ml of samples. The detection limits based on 3 sigma of the blank signals were 0.11 and 0.12 microgram l-1 for total and inorganic mercury, respectively. The relative standard deviation of ten independent measurements were 2.8 and 2.2% for 10 micrograms l-1 and 8.8 and 9.0% for 0.1 microgram l-1 amounts of total and inorganic mercury, respectively. The recoveries of 0.3, 0.6 and 8 micrograms l-1 of inorganic and organic mercury added to fish-eggs oil samples ranged from 93.0 to 94.8% and from 100 to 106%, respectively. Good agreement with those values obtained for total mercury content in real samples by electrothermal atomic absorption spectrometry was also obtained, differences between mean values were < 7%. With the proposed procedure, 22 proteropterous catfish-eggs oil samples from the northwestern coast of Venezuela were measured; while the organic mercury lay in the range 2.0 and 3.3 micrograms l-1, inorganic mercury was not detected.     

A novel derivatisation procedure for inorganic mercury(II) for HPLC analysis

Summary A new procedure for derivatisation of inorganic mercury(II) to diphenylethynylmercury with simultaneous extraction into dichloromethane is proposed. The organomercury derivative is effectively analysed by HPLC using UV detection. The calibration curve is linear over three orders of magnitude (0.02–50 mg L^–1 Hg); the detection limit is 0.1 ng Hg. A preliminary study of the effect of potential interfering agents, in particular Cu(II), Zn(II), Cd(II), Pb(II), and cysteine, and applications of the present methodology to real environmental samples are presented.     

Optimization of the extraction for the determination of arsenic species in plant materials by high-performance liquid chromatography coupled with hydride generation atomic fluorescence spectrometry

A study has been conducted for the separation and the determination of arsenic species in plants using high-performance liquid chromatography–hydride generation atomic fluorescence spectrometry with emphasis on sample extraction procedures. Various extraction solvents have been applied to extract arsenic species from plants in order to investigate the uptake, transfer and accumulation processes of arsenic. The method was optimized with respect to the selection of extraction solvent, extraction time and the number of extraction steps. The analytical procedure has been validated by analyzing standard reference material GBW 82301 (peach leaves) and successfully used for the arsenic speciation in plants grown on contaminated soil near an arsenic mine. Inorganic arsenic, especially arsenate (As(V)) appears to be the major component in plants and organic arsenic species of monomethylarsenic acid and dimethylarsenic acid were detected at low concentrations.     

Sample treatment selection for routine mercury speciation in seafood by gas chromatography–atomic fluorescence spectroscopy

A general analytical strategy for mercury speciation in seafood samples has been proposed to increase sample throughput. This consists of the initial determination of total mercury content, and then mercury speciation using gas chromatography coupled to atomic fluorescence spectroscopy. The appropriate sample treatment for mercury speciation is selected between a method based on aqueous ethylation with sodium tetraethylborate (Approach A: a rapid methodology for samples with methylmercury concentrations between 150 and 2000 ng g^?1) and another one based on the determination of organomercury chlorides (Approach B: a much more time‐consuming methodology, applicable to samples with methylmercury at 1.2–200 ng g^?1). Both procedures have been used together for the analysis of bivalves and fish samples. Copyright © 2005 John Wiley & Sons, Ltd.     

断续流动-氢化物发生-原子荧光光谱法测定试剂硝酸钾中的痕量汞

采用断续流动-氢化物发生-原子荧光光谱法对化学试剂KNO3中的痕量汞进行了测定。确定了测定KNO3试剂中汞的最佳分析条件。检出限为0.05ng/mL,样品加标回收率为97.8%~101.2%。     

Determination of mercury in microwave-digested soil by laser-excited atomic fluorescence spectrometry with electrothermal atomization

A sample digestion procedure was developed which employs microwave heating of soil and sediment in concentrated nitric acid in a high-pressure closed vessel. Complete dissolution of mercury into the sample solution occurs within 5 min at 59 W/vessel without loss of analyte through overpressurization. Laser-excited atomic fluorescence spectrometry with electrothermal atomization (LEAFS-ETA) was used as the detection method. The scheme uses a two-step excitation, with λ₁ = 253.7 nm and λ₂ = 435.8 nm. Direct line fluorescence was measured at 546.2 nm. The absolute instrumental limit of detection was 14 fg; 1.4 pg/ml with a 10 μl sample injection. The recoveries of mercury in two spiked samples were 94 and 98%. The SRM 8406 (Mercury in River Sediment) was digested and analyzed for mercury, and the results (58.4 ± 1.8 ng/g) agreed well with the reference value of 60 ng/g. The results obtained by LEAFS-ETA with microwave sample digestion are in good agreement with those found by cold vapor atomic absorption spectrometry with EPA Series Method 245.5 sample digestion, which is one of the most commonly used methods for the determination of mercury in soil.     

Efficiency of solvent extraction methods for the determination of methyl mercury in forest soils

Methyl mercury was determined by gas chromatography, microwave induced plasma, atomic emission spectrometry (GC-MIP-AES) using two different methods. One was based on extraction of mercury species into toluene, pre-concentration by evaporation and butylation of methyl mercury with a Grignard reagent followed by determination. With the other, methyl mercury was extracted into dichloromethane and back extracted into water followed by in situ ethylation, collection of ethylated mercury species on Tenax and determination. The accuracy of the entire procedure based on butylation was validated for the individual steps involved in the method. Methyl mercury added to various types of soil samples showed an overall average recovery of 87.5%. Reduced recovery was only caused by losses of methyl mercury during extraction into toluene and during pre-concentration by evaporation. The extraction of methyl mercury added to the soil was therefore quantitative. Since it is not possible to directly determine the extraction efficiency of incipient methyl mercury, the extraction efficiency of total mercury with an acidified solution containing CuSO₄ and KBr was compared with high-pressure microwave acid digestion. The solvent extraction efficiency was 93%. For the IAEA 356 sediment certified reference material, mercury was less efficiently extracted and determined methyl mercury concentrations were below the certified value. Incomplete extraction could be explained by the presence of a large part of inorganic sulfides, as determined by ¶x-ray absorption near-edge structure spectroscopy (XANES). Analyses of sediment reference material CRM 580 gave results in agreement with the certified value. The butylation method gave a detection limit for methyl mercury of 0.1 ng g^–1, calculated as three times the standard deviation for repeated analysis of soil samples. Lower values were obtained with the ethylation method. The precision, expressed as RSD for concentrations 20 times above the detection limit, was typically 5%.     

Atomic fluorescence spectrometry combined with reduction aeration for the determination of mercury in biological samples

A sensitive atomic fluorescence system for the determination of mercury was optimized. The system consists of a continuous-flow mercury vapour generator coupled to a fluorescence spectrometer specific for mercury. A new gas-liquid separator was developed. A detection limit of 0.9 ng Hg 1^?1 was obtained. The system was combined with a microwave oven for dissolving samples in closed Teflon PFA vessels. Accurate results were obtained for certified reference materials, and biological samples such as urine and hair were analysed.     

Determination of ultratrace bismuth in milk samples by atomic fluorescence spectrometry

A sensitive procedure was developed for determination of bismuth (Bi) in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion with HNO3 and H2O2. The method provides a sensitivity of 1832 fluorescence units (ng/mL) with a detection limit of 0.01 ng/mL, which corresponds to 20 pg absolute limit of detection, equivalent to 0.50 ng/g in the original sample. Application of the methodology to cow milk samples from the Spanish market showed the presence of Bi at a concentration of 11.8-28.8 ng/g, which compared well with data obtained after dry ashing of samples and with data obtained by inductively coupled plasma-mass spectrometry after microwave-assisted digestion.     

Ultrasensitive determination of mercury in human saliva by atomic fluorescence spectrometry based on solidified floating organic drop microextraction

We report on a new, rapid and simple method for the determination of ultra-trace quantities of mercury ion in human saliva. It is based on solidified floating organic drop microextraction and detection by cold vapor atomic fluorescence spectrometry (CV-AFS). Mercury ion was complexed with diethyldithiocarbamate, and the hydrophobic complex was then extracted into fine droplets of 1-undecanol. By cooling in an ice bath after extraction, the droplets in solution solidify to form a single ball floating on the surface of solution. The solidified microdrop containing the mercury complex was then transferred for determination by CV-AFS. The effects of pH value, concentration of chelating reagent, quantity of 1-undecanol, sample volume, equilibration temperature and time were investigated. Under the optimum conditions, the preconcentration of a 25-mL sample is accomplished with an enrichment factor of 182. The limit of detection (3σ) is 2.5?ng?L^?1. The relative standard deviation for seven replicate determinations at 0.1?ng?mL^?1 level is 4.1%. The method was applied to the determination of mercury in saliva samples collected from four volunteers. Two volunteers having dental amalgam fillings had 0.4?ng?mL^?1 mercury in their saliva, whereas mercury was not detectable in the saliva of two volunteers who had no dental fillings.

Efficiency of solvent extraction methods for the determination of methyl mercury in forest soils

Methyl mercury was determined by gas chromatography, microwave induced plasma, atomic emission spectrometry (GC-MIP-AES) using two different methods. One was based on extraction of mercury species into toluene, pre-concentration by evaporation and butylation of methyl mercury with a Grignard reagent followed by determination. With the other, methyl mercury was extracted into dichloromethane and back extracted into water followed by in situ ethylation, collection of ethylated mercury species on Tenax and determination. The accuracy of the entire procedure based on butylation was validated for the individual steps involved in the method. Methyl mercury added to various types of soil samples showed an overall average recovery of 87.5%. Reduced recovery was only caused by losses of methyl mercury during extraction into toluene and during pre-concentration by evaporation. The extraction of methyl mercury added to the soil was therefore quantitative. Since it is not possible to directly determine the extraction efficiency of incipient methyl mercury, the extraction efficiency of total mercury with an acidified solution containing CuSO4 and KBr was compared with high-pressure microwave acid digestion. The solvent extraction efficiency was 93%. For the IAEA 356 sediment certified reference material, mercury was less efficiently extracted and determined methyl mercury concentrations were below the certified value. Incomplete extraction could be explained by the presence of a large part of inorganic sulfides, as determined by x-ray absorption near-edge structure spectroscopy (XANES). Analyses of sediment reference material CRM 580 gave results in agreement with the certified value. The butylation method gave a detection limit for methyl mercury of 0.1 ng g(-1), calculated as three times the standard deviation for repeated analysis of soil samples. Lower values were obtained with the ethylation method. The precision, expressed as RSD for concentrations 20 times above the detection limit, was typically 5%.     

Gas chromatography coupled with atomic absorption spectrometry — a sensitive instrumentation for mercury speciation

New instrumentation for the speciation of mercury is described, and is applied to the analysis of natural water samples. The separation of mercury species is effected using gas chromatography of derivatized mercury species on a widebore capillary column. The solvent is vented using a bypass valve and the separated mercury species are pyrolysed on-line at 800°C for production of mercury atoms. These are then detected by atomic absorption spectrometry (AAS) at the 253.7 and 184.9 nm lines simultaneously in a quartz cuvette. The use of the 184.9 nm line provides a more than five-fold increase in sensitivity compared with the conventional 253.7 nm line and an absolute detection limit of 0.5 pg of mercury. The dynamic range of the combined analytical lines provides a linear response over more than three orders of magnitude. A number of organic compounds not containing mercury are also detected following pyrolysis, especially at the 184.9 nm line. These background species must not co-elute at the retention times for methyl- and inorganic mercury, as otherwise a positive interference would result. By maximizing the chromatographic resolution and minimizing the band broadening in the cuvette by use of a make-up gas, the retention times of interest are freed from co-eluting background peaks.The instrumentation has been applied to the determination of ng l⁻¹ concentrations of methyl- and inorganic mercury in Lake Constance, Germany and within the Lake Constance drinking water supply organization, Bodenseewasserversorgung (BWV). The accuracy for the sum of methyl- and inorganic mercury has been assessed by comparison with an independent method for total mercury based on AAS detection implemented at BWV. Relative detection limits using 1 litre water samples and 15 ml injections of the final hexane extract were 0.03 ng l⁻¹ for methylmercury and 0.4 ng l⁻¹ for inorganic mercury based on the 3j criterion.     

Atomic fluorescence spectrometry of mercury: principles and developments

Atomic fluorescence spectrometry (AFS) of mercury is very sensitive and the AFS system is an excellent detector for mercury analysis. The first part of this review covers the principles of determination of mercury by AFS. The second part delineates the loss and increase of mercury through its transfer between the gas and solution phases. The third part addresses some possible interferences in the determination of mercury by AFS. The fourth part describes preconcentration techniques for mercury species. In the fifth part, methods for total and selective determination of mercury are described. In the sixth part, various types of automated and semi-automated procedures for the determination of mercury are summarized. Finally, representative biological and environmental certified reference materials (CRMs) for mercury analysis are presented and the availability of CRMs in checking the accuracy and precision of the methodologies is briefly described.     

Determination of ochratoxin A at part-per-trillion level in Italian salami by immunoaffinity clean-up and high-performance liquid chromatography with fluorescence detection

A fast high-performance liquid chromatography method has been devised for the determination of ochratoxin A (OTA) in Italian salami in the low part-per-trillion (pg/g) level. The samples were extracted with ethyl acetate and purified by immunoaffinity column (IAC). The IAC eluate could be directly injected or previously concentrated 10-fold. Recovery at 0.5 and 1 ng/g was 77 +/- 4%. The between-day coefficient of variation measured over 5 days on samples spiked at 1 ng/g was 8%. The developed method required a relatively small volume of non-halogenated organic solvent and the whole procedure was simpler and faster compared to other existing procedures. The limit of detection was 0.06 ng/g that could be even lowered using a preconcentration step. A total of 30 salami samples were analysed using this procedure; the most contaminated sample was found to have OTA concentration at 0.4 ng/g level.