Determination Of Total Hg Research Articles

A new vapor generation system for mercury species based on the UV irradiation of mercaptoethanol used in the determination of total and methyl mercury in environmental and biological samples by atomic fluorescence spectrometry

A new vapor generation system for mercury (Hg) species based on the irradiation of mercaptoethanol (ME) with UV was developed to provide an effective sample introduction unit for atomic fluorescence spectrometry (AFS). Preliminary investigations of the mechanism of this novel vapor generation system were based on GC-MS and FT-IR studies. Under optimum conditions, the limits of determination for inorganic divalence mercury and methyl mercury were 60 and 50 pg mL(-1), respectively. Certified reference materials (BCR 463 tuna fish and BCR 580 estuarine sediment) were used to validate this new method, and the results agreed well with certified values. This new system provides an attractive alternative method of chemical vapor generation (CVG) of mercury species compared to other developed CVG systems (for example, the traditional KBH(4)/NaOH-acid system). To our knowledge, this is the first systematic report on UV/ME-based Hg species vapor generation and the determination of total and methyl Hg in environmental and biological samples using UV/ME-AFS.

Ultra-trace determination of mercury in water by cold-vapor generation isotope dilution mass spectrometry

Determination of total Hg at the ppt level in water using cold vapor generation and inductively coupled plasma mass spectrometry for calibration by isotope dilution (ID) with both sector field (SF-ICP-MS) and time-of-flight MS (ICP-TOF-MS) detection is described. Samples were reduced on-line in a flow injection manifold with SnCl2 to generate Hg vapor for both steady-state and transient sample introduction following gold trapping. No significant difference in final Hg concentrations was detected using either approach. Certified reference material ORMS-3 river water (NRCC, Ottawa, Canada) was used for method validation. Mercury concentrations of 12.75 ± 0.24 and 12.34 ± 0.11 pg g−1 (mean and one standard deviation, n = 4) were obtained using steady-state generation with SF-ICP-MS and ICP-TOF-MS, respectively, in agreement with the certified value of 12.6 ± 1.1 pg g−1 (combined uncertainty, k = 2). Concentrations of 12.55 ± 0.41 and 12.65 ± 0.30 pg g−1 (one standard deviation, n = 4) were obtained following gold trapping and SF-ICP-MS and ICP-TOF-MS detection, respectively. Compared with SF-ICP-MS, a 2-fold enhancement in the precision of the measured 200Hg/201Hg and 202Hg/201Hg ratios in a 100 ppt Hg standard solution was obtained using ICP-TOF-MS. Consequently, improved precisions of 0.87–2.33% RSD in Hg concentrations obtained by steady-state and transient signal acquisition, respectively, in ORMS-3 were obtained using ICP-TOF-MS, compared with 1.88–3.25% RSD obtained with SF-ICP-MS. Method detection limits (LODs, three times standard deviation) of 0.024 and 0.15 pg g−1 for Hg using direct CV and following gold trapping, respectively, were obtained using SF-ICP-MS. These were superior to corresponding LODs of 0.30 and 0.87 pg g−1 obtained using ICP-TOF-MS as a result of its 15-fold lower sensitivity.

Determination of inorganic and total mercury in biological samples treated with tetramethylammonium hydroxide by cold vapor atomic absorption spectrometry using different temperatures in the quartz cell

A very simple procedure is proposed for the determination of total and inorganic Hg in biological materials. Organic Hg (methylmercury) can be obtained from the difference. After treating the sample at room temperature with tetramethylammonium hydroxide (TMAH), inorganic Hg is obtained by cold vapor atomic absorption spectrometry (CV-AAS), keeping the quartz cell at room temperature, while total Hg is obtained by the same technique, heating the quartz cell in an air–acetylene flame. By analyzing several biological certified materials, it was evident that the difference between the mentioned concentrations corresponds to methylmercury. Cold vapor graphite furnace atomic absorption spectrometry (CV-GF-AAS) with retention of the vapor in a heated Au-treated graphite tube was used to optimize the vapor generation conditions and also to determine total Hg. In a general way, the concentrations obtained by both techniques were in agreement with the certified values or with differences of the certified values for total, Hg2+ and CH3Hg+, according to the t-test for a 95% confidence level. Total Hg results obtained by the two techniques were also in agreement. The relative standard deviations were lower than 10% for most of the results. The detection limits in the sample were: 0.13 μg g−1 for total Hg and 0.025 μg g−1 for Hg2+ by CV-AAS. The detection limit for total Hg by CV-GF-AAS was 0.001 μg g−1. It is amazing how this very simple method is able to provide very important information on mercury speciation.

Determination of total mercury in seafood by cold vapor-atomic absorption spectroscopy (CVAAS) after microwave decomposition

A method was developed for determination of total Hg in seafood using 10% w/v SnCl 2 · 2H 2O and continuous flow CVAAS after microwave decomposition in closed vessels. Seafoods were decomposed with 5 mL HNO 3 and 1 mL 1% w/v NaCl at 200 °C, transferred to polypropylene tubes containing 3.5 mL HCl, and diluted to 50 mL with H 2O. Standards were prepared in diluent containing 10% v/v HNO 3, 7% v/v HCl, and 0.02% w/v NaCl. Potential interference by 22 elements was evaluated. Interference by Se and Au was observed. Stability of standard solutions in HNO 3, HCl and NaCl was evaluated. Stabilizing effect of chloride was demonstrated. Results for six reference materials containing 0.0371–1.59 mg/kg Hg were 86–106% of certificate values. Concentrations in 11 varieties of seafood were 0.015–1.78 mg/kg. Average recoveries of inorganic and organic Hg added to seafood were 102% and 99%, respectively; average recoveries from fortified method blanks were 100% and 97%, respectively. The limits of quantitation were 0.0022 and 0.011 mg/kg in seafoods and reference materials, respectively.

Determination of total mercury in whole blood by flow injection cold vapor atomic absorption spectrometry with room temperature digestion using tetramethylammonium hydroxide

An improved method is described for the determination of total Hg in whole blood based on flow injection cold vapor atomic absorption spectrometry (FI-CVAAS). Aliquots of whole blood (300 µl) are diluted 1 + 1 v/v with 10% v/v tetramethylammonium hydroxide (TMAH) solution, incubated for 1 h at room temperature and then further diluted 1 + 4 v/v with 2% v/v HCl. The TMAH approach is directly compared to a previously published method that utilizes an on-line microwave-assisted heating step as part of the FI arrangement. Thus, the key issue addressed here is the elimination of the on-line microwave digestion step from the FI manifold, because of problems observed with precipitation in the reaction coil and high back pressure in FI manifold. Matrix-matched calibration standards are used and the method detection limit (3σ) is 0.2 µg l−1. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from the National Institute of Standards and Technology (NIST). Additional validation data are provided based on the analysis of whole blood materials from the New York State Department of Health's Proficiency Testing Program for Trace Elements and from the trace elements intercomparison program operated by the Institut National de Sante Publique du Quebec, Canada. Accuracy (−2.5%) and precision (<6.0% repeatability and <10% intermediate precision) of the TMAH method compare favorably with values obtained for the on-line microwave method (<10.0% repeatability and <15% reproducibility), and the TMAH method is essentially free of the disadvantages associated with the latter method.

Routine, High-Sensitivity, Cold Vapor Atomic Absorption Spectrometric Determination of Total Mercury in Foods after Low-Temperature Digestion

A cold vapor atomic absorption spectrometric method was developed for the subnanogram-per-gram determination of total Hg in a wide variety of foods. Foods were weighed into 50 mL polypropylene centrifuge tubes and dried without charring at 55 degrees C in a circulating oven. Samples were then digested at 58 degrees C with HNO3, HCl, and H2O2. After matrix modification with solutions of 2% Mg(NO3)2, 0.01% Triton X-100, and Cu(II) at 10 microg/mL, samples were analyzed by using a CeTAC Technologies M-6000A dedicated Hg analyzer. Based on a 2 g sample weight, the detection limit of the method over 12 batches averaged 0.30 ng/g wet weight and ranged from 0.03 to 0.6 ng/g. Recoveries of Hg added to 17 different foods, analyzed in a routine manner, averaged 97%, and individual recoveries ranged from 77 to 107%. Accuracy was confirmed by analysis of 7 biological reference materials from the National Research Council of Canada and the National Institute of Standards and Technology. Stabilization of low concentrations of Hg in solutions containing no sample was required to prevent loss of Hg from blanks. In a comparison of NaCl, potassium dichromate, and Au(II), chloride was much more effective for stabilization than the other two, and HCl was used for subsequent stabilization.

On-line pre-concentration of Hg in blood and urine and determination by CVAAS

A method for total Hg determination in urine and blood by cold vapour atomic absorption spectrometry (CVAAS), after on-line separation/pre-concentration, is described. The samples were acid-digested in closed vessels using a HNO3/HClO4 mixture and heating in a microwave oven. The Hg determination was accomplished by retention of Hg complexes formed with the ammonium salt of O,O-diethyldithiophosphoric acid (DDTP) on C18 immobilized on silica in a column. The analyte was eluted with methanol, which was mixed with a reducing agent (NaBH4) on-line, and measured. The optimum conditions for the Hg pre-concentration, such as DDTP concentration, acid concentration and acid nature (HNO3 and HCl), and the solutions flow rates were experimentally established. The conditions for on-line cold vapour generation, including the acid concentration in the eluant (methanol), the NaBH4 concentration and the carrier gas (Ar) flow rate, were optimised. The limit of detection (LOD), based on three times the standard deviation of the sample blank (10 consecutive measurements), of the proposed method was 8 ng l−1 of Hg (by processing 7.6 ml of solution) and the LOD for Hg in the samples was 20 ng l−1. At a concentration of 50 ng l−1 of Hg solution, the relative standard deviation was less than 6% for five replicates of the sample solution or calibration solution. The calibration curves were linear from 25 ng l−1 to 600 ng l−1 of Hg and a sample throughput of 24 measurements per hour was possible. The accuracy of the method was checked by analysis of a certified urine sample and spiked blood samples. The proposed method was employed for analysis of real blood and urine samples.

Determination of total urinary mercury by on-line sample microwave digestion followed by flow injection cold vapour inductively coupled plasma mass spectrometry or atomic absorption spectrometry.

The total mercury content in urine was determined by inductively coupled plasma mass spectrometry with the so-called cold vapour method after on-line oxidative treatment of the sample in a microwave oven (FI-MW-CV-ICPMS). Use of a KBr/KBrO(3) mixture, microwave digestion, and the final oxidation with KMnO(4), assure the complete recovery of the organic forms of Hg which would be difficult to determine otherwise if using only the CV-ICPMS apparatus. Quantitative recoveries were obtained for phenyl Hg chloride (PMC), dimethyl Hg (DMM), Hg acetate (MA) and methyl Hg chloride (MMC). Use of automatic flow injection microwave systems (FI-MW) for sample treatment reduces environmental contamination and allows detection limits suitable for the determination of reference values. Since no certified reference materials were commercially available in the concentration ranges of interest, the accuracy of the proposed procedure has been assessed by analysing a series of urine samples with two independent techniques, ICP-MS and AAS. When using the FI-MW-CV-ICP-MS technique, the detection limit was assessed at 0.03microg/L Hg, while with FI-MW-CV-AAS it was 0.2microg/L Hg. The precision of the method was less than 2-3% for FI-MW-CV-ICP-MS and about 3-5% for FI-MV-CV-AAS at concentrations below 1microg/L Hg. These results show that ICP-MS can be considered as a "reference technique" for the determination of total urinary Hg at very low concentrations, such as are present in non-exposed subjects.

Determination of mercury by continuous flow cold vapor atomic fluorescence spectrometry using micromolar concentration of sodium tetrahydroborate as reductant solution.

Systematic experiments were conducted to evaluate and compare the analytical figures of merit of two reducing agents (SnCl2 and NaBH4) in a continuous flow cold vapor atomic fluorescence mercury analyzer. It was found that sodium tetrahydroborate can efficiently reduce Hg2+ in various environmental samples at a concentration as low as 10 microM (ca. 3.8 x 10(-5)% w/v). Most commonly encountered transition metals (Fe2+, Fe3+, Zn2+, Cu2+, Ni2+, Pb2+ and Cr3+) did not interfere with total Hg determination. No interference from hydride-forming elements (Se4+, Sb3+ and As3+) was observed. Interference caused by Mn2+ and Ag+ could be readily removed by dilution and by using appropriate modification of the reaction matrix. A higher concentration of NaBH4 (0.1 M) is stable for I month when stored in the NaOH matrix (0.2 M) and at low temperature (4 degrees C). A working solution of NaBH4 can be freshly prepared by dilution. With NaBH4, the whole continuous flow system is kept clean much more easily as no precipitate is formed, which in turn considerably reduces memory effects, simplifies analytical operation and reduces the chemical cost six-fold.

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.

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.

Mercury determination in environmental samples using EDXRF and CV-AAS

The determination of total Hg in various environmental matrices was investigated using energy-dispersive x-ray fluorescence (EDXRF) spectrometry on both powdered and digested samples and cold vapor atomic absorption spectrometry (CV-AAS) on digested samples. Several microwave decomposition procedures were evaluated. The use of different acid mixtures, microwave power settings and decomposition times were compared, in addition to the analysis of wet and freeze dried samples. A set of standard reference samples were used to evaluate the procedures. An H 2 SO 4 -HNO 3 -H 2 O 2 mixture was found to be optimal for the complete mineralization and digestion of biological samples for Hg by CV-AAS, whereas for EDXRF both HNO 3 -H 2 O 2 and H 2 SO 4 -HNO 3 -H 2 O 2 mixtures gave good results. The detection limit of EDXRF could be significantly decreased (from 0.2 μg g -1 to 0.058 μg g -1 ) by performing the analysis on digested samples. Good agreement was obtained between the EDXRF and CV-AAS analysis. The results were also in good agreement with certified values. The methods were applied to environmental samples (coal, vegetation, fish and sediment) and human hair in a coal mining area and in locations where coal is used for cooking in Vietnam.

Determination of atmospheric Hg by collection on iodated carbon, acid digestion and CVAFS detection

An established industrial monitoring technique has been refined to allow the accurate determination of total gaseous Hg in air at background levels (1–3 ng·m−3). Samples are collected under vacuum through a commercially available iodide-impregnated carbon trap. For analysis, the trap is digested in a 7∶3 (v/v) mixture of HNO3+H2SO4, and an aliquot of the digest analyzed by SnCl2 reduction, dual gold amalgamation, and cold vapor atomic fluorescence spectrometric (CVAFS) detection. The traps exhibit little breakthrough (<5%) under flow rates of up to 1.0 l·min−1 for periods up to 10 days. The mean value for the blank on the half traps was found to be 0.40±0.16 ng (n=20), resulting in a 3 α detection limit of 0.07 ng·m (1 week sample at 1.0 L·m−3). Replicate field collections show a between-trap RSD of ± 6.4%, while field intercomparison with gold trapping resulted in 104±20% recovery in the 1–4 ng/m3 concentration range.

Spectrofluorometric method for determination of the total mercury content in natural waters

A simple and highly selective spectrofluorometric method for the determination of the total mercury (Hg) in natural waters is described. Fluorescence quenching of rhodamine B with Hg(II) in the presence of iodide, after a concentration step, has been made the basis of this sensitive method. Organic and inorganic Hg compounds in water samples were decomposed with sulphuric acid and potassium permanganate. Precipitated manganese dioxide and excess oxidants (permanganate) were destroyed with hydroxylammonium chloride. Hg(II) was reduced by tin(II) chloride and Hg vapour driven by an air stream into an absorption solution containing potassium permanganate and sulphuric acid, using a closed, recirculating air stream. In this solution fluorescence quenching of rhodamine B at an excitation wavelength of 485 nm and emission wavelength of 586 nm was measured. This method is suitable for the determination of total Hg in drinking and surface waters. The method gives reliable results down to a concentration of 0.5 micrograms Hg per litre of water. The water samples analysed by this method gave a mean recovery and standard error of 97.3 +/- 2.39 for added Hg.

Sample weight and digestion temperature as critical factors in mercury determination in fish

The concern about mercury (Hg) pollution of the marine environment started with the well publicized case of Minimata (Japan) where in the 1950s several persons died or became seriously ill after consuming fish or shellfish containing high levels of methylmercury. It is now accepted that Hg contaminated seafoods constitute a hazard to human health. To safeguard humans, accurate determination of Hg in marine biota is, therefore, very important. Two steps are involved in the determination of total Hg in biological materials: (a) decomposition of organic matrix (sample preparation), and (b) determination of Hg in aliquot samples. Although the procedures for determining Hg using the cold vapor technique are well established, sample preparation procedures have not been standardized. In general, samples of marine biota have been prepared by digesting different weights at different temperatures, by using mixtures of different chemicals and of varying quantities, and by digesting for variable durations. The objectives of the present paper were to evaluate the effects of sample weights and digestion temperatures on Hg determination in fish.

Mercury accumulation in delphinidae

The aim of this work is an attempt to synthetize the different results of our researches on dolphin's contamination by Hg and their interpretation. It is based on the results obtained following the total Hg determination in several organs of 35 specimens of Stenella coeruleoalba stranded on French Atlantic and Mediterranean coasts and 45 Stenella attenuata captured in the Eastern tropical Pacific. Considering our present knowledge on Hg ecotoxicological processes, the trophic route, via cumulative Hg transfers through the marine trophic network, can be considered as the major contamination route for the dolphins. However, considering the influence of the geographical origin of the individuals it also seems reasonable to assume that the principal contamination source of the high Hg concentrations observed in pelagic dolphins are natural metal deposits.

Determination of methylmercury in biological certified reference materials

Various isolation techniques (ion — exchange, extraction, volatilization, distillation) were used to separate organic Hg, followed by cold vapor atomic absorption spectrophotometry (CV AAS) for determination of total organic Hg, and/or gas chromatography (electron capture detector) for determination of McHg and EtHg if present. Some currently available CRMs with certified total Hg values, including NBS Oyster Tissue 1566, NBS Horse Kidney H-9, IAEA Fish Flesh Homogenate MA-A-2/TM, IAEA Fish Tissue Lyophilized MA-B-3/TM, IAEA Mussel Tissue MA-M-2/TM, IAEA Copepod Homogenate MA-A-1/TM, IAEA Shrimp Tissue Homogenate MA(S)-MEDPOL-86/TM, NIES No.5 Human Hair, and NIES No.9 Sargasso were investigated. CRMs from the National Research Council of Canada (TORT-1, DORM-1, DOLT-1) which have recently been certified for MeHg, were also analyzed. Results obtained by different approaches show good agreement. The advantage of GC which permits different organic compounds to be determined was demonstrated in the case of some IAEA CRMs where both McHg and EtHg was found; indirect CV AAS gives the results for total organic Hg. Therefore it can be suggested that various currently available CRMs for total Hg can also be used for establishment of recommended values for McHg (and EtHg if present) and organic Hg. However, additional intercalibration exercises or data from other laboratories are necessary to obtain a consensus.

The analysis of vegetation for total mercury

Over four hundred vegetation samples were collected for total Hg determination as part of a biogeochemical survey in the Precambrian Shield region near Huntsville, Ontario. An objective of the survey was to obtain accurate data describing the spatial and temporal variation of Hg concentrations in vegetation. Five tree species, clubmosses, mosses, lichen and fungi were collected along three transects each 8 to 10 km long. The samples were digested using a hot H2SO4/HNO3 mixture followed by cold-vapor AAS detection. Very low detection limits (less than 1.0 ng g−1) were achieved by performing the analyses in a clean, Hg-free laboratory. The Hg concentration of coniferous needles did not vary significantly over eight weeks of the summer, but did vary significantly between first and second year growth. In all tree species examined, Hg concentrations in needles/leaves were two to three times as high (by dry weight) as that in twig tissue from the same branch. Differences in Hg content between tissues of different types and ages constituted a major source of within-site variation between plants of the same species.

Comparison of Different Analytical Techniques for the Determination of Organic Mercury

Abstract Methods for the determination of (1) total organic mercury (Hg) using an extraction +neutron activation analysis, (2) the sum of methyl-Hg+phenyl-Hg using 131I−-Cl− exchange and (3) methyl-Hg using two different Westöö modifications, have been compared. Sample materials were 8 falcon livers, 5 pike livers and 2 pike muscles. Although differences were found between the methods, interaction effects caused by either sample inhomogeneity or bad performance of the analytical methods impeded a clear interpretation of the comparison. Total Hg in the samples was determined by neutron activation analysis (NAA) and atomic absorption spectrometry. The accuracy of the total Hg determination using NAA was verified by the analysis of certified reference material. In addition to the other organic Hg determinations phenyl-Hg was determined separately in some of the samples by an isotope exchange method using 203Hg2+. The main conclusion of the study was that there is a demand for reference materials certified for at least total organic Hg and methyl-Hg.