Effects of sample preservation and storage on mercury speciation in natural stream water

Despite an increasing focus on low level methods for determination of mercury species in water over the last decades, few studies have paid attention to direct effects of different sample preparation methods (i.e. preservation techniques) on natural freshwater samples. In this study we show how different preservation techniques give significantly different concentrations of total and methylmercury in freshwaters (9 and 14% on average, respectively). Natural stream samples from a forested lake catchment were studied. Mean stream sample concentrations of total (3.6 ng/L) and methylmercury (0.06 ng/L) reflect levels typical for pristine humic boreal catchments. The main reason for the observed average differences in total and methylmercury concentrations is the use of one instead of two sample bottles and timing of sample acidification, respectively.     

Inorganic mercury and methylmercury determination in polluted waters by HPLC coupled to cold vapour atomic fluorescence spectroscopy

A systematic study of Hg²⁺ and CH₃Hg⁺ (MeHg⁺) speciation using hyphenated techniques, was performed for high-performance liquid chromatography coupled to on-line UV irradiation and cold-vapour atomic fluorescence spectroscopy (HPLC-UV-CV-AFS). First, a comparative study of the behaviour of three mobile phase compositions (using tetrabutylammonium bromide (TBAB), L-cysteine and ammonium pyrrolidinedithiocarbamate (APDC)) is presented. The separation and detection system was optimised by considering factors that modify fluorescence signal and the separation such as, the addition of different percentages of an organic modifier (methanol (MeOH) and acetonitrile (ACN)) to the mobile phase, the type of reducing agent used (SnCl₂ and NaBH₄) and the potential memory effects of the material of which the injection system is made (stainless steel, PEEK). The mobile phase selected for its sensitivity was a mixture 80?:?20 MeOH?:?0.0015?mol?l^–1 APDC and 0.01?mol?l^–1 NH₄CH₃COO (pH 5.5). The detection and quantification limits were close to 1.5 and 5?µg?l^?1 for both species (as Hg), respectively. Recoveries obtained using fortified water samples of distinct origin (soft mineral, tap, river, seawater, and wastewater), ranged from 90 to 115% for concentrations about 2 and 20 times over quantification limits. Good repeatability was obtained (about 5%) independently of the concentrations, with reproducibility values about 20% at low concentrations and 5–10% at higher concentrations. Our proposed method proved to be straightforward for use by environmental laboratories for routine Hg²⁺ and MeHg⁺ determinations in polluted water samples.     

Inter‐laboratory validation of EPA method 3200 for mercury speciation analysis using prepared soil reference materials

Determinations of the concentration of individual mercury species from environmental samples have increased significantly over the past decade. The techniques used for the determination of mercury species in soils or sediments generally involve a series of analytical steps (extraction, separation, detection) that may all be prone to systematic errors. An inter‐laboratory validation study of the EPA draft method 3200 was conducted under the auspices of the United States Environmental Protection Agency on two specifically prepared soil matrices. The study was performed successfully by a limited number of participating laboratories. Evaluation of the data demonstrates that the method is more highly efficient for extracting the highly toxic methylmercury than inorganic mercury. The proposed method does not induce transformation of methylmercury to inorganic mercury. Copyright © 2004 John Wiley & Sons, Ltd.     

Determination of mercury(II), methylmercury and ethylmercury in the ng/ml range with an electrochemical enzyme glucose probe

Hg(II), methylmercury and ethylmercury have been determined with an electrochemical glucose probe. Mercury and its compounds inhibit the enzyme invertase which, in presence of its substrate, sucrose, produces glucose. When invertase is in presence of mercury its activity decreases; this causes a decrease of glucose production, which is monitored by the glucose sensor and correlated to the concentration of mercury in solution. Parameters such as pH, enzyme concentration, substrate concentration, and reaction and incubation time were optimized. Results showed that mercury, methylmercury and ethylmercury can be detected directly in aqueous solution in the range 2–10 ng/ml.     

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.     

The determination of methylmercury in biological samples by HPLC coupled to ICP‐MS detection

The use of high‐performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP‐MS) for the determination of methylmercury (MeHg⁺) in fish tissue and hair samples is described. Analysis of these sample types is required when carrying out biomonitoring studies to determine human dietary exposure to this toxic mercurial compound. The developed method used a mobile phase containing an organic modifier and a sulfydryl compound (1:1 v/v methanol:water containing 0.01% v/v 2‐mercaptoethanol) to limit peak tailing and aid separation. The chromatographic separation was coupled to the ICP‐MS detector via a short piece of PEEK tubing, attached to the nebulizer. A cooled spraychamber and oxygen addition post‐nebulization were required to limit the solvent loading on the plasma and reduce carbon build‐up on the cones, respectively. The sample preparation procedure employed a drying step followed by digestion of the sample using tetramethylammonium hydroxide (TMAH) and heating in an open vessel microwave system. Two fish tissue certified reference materials (CRM), tuna fish CRM 463 and 464 (BCR, Brussels), a tuna fish proficiency test sample, IMEP‐20 (IRMM, Geel, Belgium) and a hair CRM NIES no. 13 (National Institute of Environmental Science, Japan), were used to evaluate the method. The recovery of MeHg⁺ for these four materials was between 83 and 100%, with precisions better than 6% for three separate extractions of the different materials. The limit of quantitation for MeHg⁺ using the developed protocol was 0.5 µg Hg g^?1. The stability of MeHg⁺ in the fish sample extracts was also assessed and losses of 14–16% were observed after storage of the extracts in a refrigerator at 5 °C, in high‐density polypropylene tubes, for 6 months. The developed protocol has been used previously with atmospheric pressure ionization mass spectrometry (API‐MS) to provide structural characterization and also with calibration via isotope dilution (IDMS) to provide high accuracy quantitation. Copyright © 2006 John Wiley & Sons, Ltd.     

The AQUA-MER databases and aqueous speciation server: A web resource for multiscale modeling of mercury speciation

To assess the chemical reactivity, toxicity, and mobility of pollutants in the environment, knowledge of their species distributions is critical. Because their direct measurement is often infeasible, speciation modeling is widely adopted. Mercury (Hg) is a representative pollutant for which study of its speciation benefits from modeling. However, Hg speciation modeling is often hindered by a lack of reliable thermodynamic constants. Although computational chemistry (e.g., density functional theory [DFT]) can generate these constants, methods for directly coupling DFT and speciation modeling are not available. Here, we combine computational chemistry and continuum-scale modeling with curated online databases to ameliorate the problem of unreliable inputs to Hg speciation modeling. Our AQUA-MER databases and web server ( https://aquamer.ornl.gov ) provides direct speciation results by combining web-based interfaces to a speciation calculator, databases of thermodynamic constants, and a computational chemistry toolkit to estimate missing constants. Although Hg is presented as a concrete use case, AQUA-MER can also be readily applied to other elements. © 2019 Wiley Periodicals, Inc.     

Laboratory and field evaluation of diffusive gradient in thin films (DGT) for monitoring levels of dissolved mercury in natural river water

The diffusive gradient in the thin films (DGT) technique was tested to measure dissolved mercury (Hg) both in laboratory aqueous solutions and in situ in river water. For this purpose, a commercial ready-to-use and specific-for-Hg DGT device was used. Each sampler consisted of a filter membrane-agarose gel as the diffusive layer and a Spheron-Thiol resin in polyacrylamide gel as the binding agent. Basic performance assays at the laboratory with this type of DGT unit confirmed the applicability of Fick's first law for DGT measurements. The diffusion coefficient of MeHg in the agarose diffusive gel was 8.50?×?10^?6?cm² s^?1 at 25°C. Several field studies were also carried out in two different rivers of the Ebro River basin (NE Spain) affected by Hg wastes released by the chlor-alkali industry. Hg concentrations determined by DGT were generally much lower than the results obtained through direct measurements of the river water. In addition, the results of a time series experiment also performed in the field show that the amount of Hg accumulated in the resin does not increase at all with the exposure time. This may be explained by the underestimation of the truly dissolved Hg fraction due to the formation of a biofilm layer on the surface of the samplers, thus clogging the filter and preventing Hg species from diffusing through it. Consequently, it was demonstrated that the DGT technique presents important limitations for measuring Hg in polluted rivers characterised by a high biomass load (eutrophic), whereas its performance was demonstrated to be correct in oligotrophic waters.     

Mercury species immobilized on sulphydryl cotton: A new candidate reference material for mercury speciation

A batch of sulphydryl cotton microcolumns was prepared and charged with a mixed Hg standard solution (methyl-, ethyl- and inorganic Hg, 10 g l^–1 as Hg, 3 ml) and stored at 4 °C in a light-tight box. At regular time intervals over a 4 month period microcolumns were removed and Hg species were quantified by gas chromatography microwave-induced plasma atomic emission spectrometry (after elution, extraction and derivatization steps). It was found that analyte recoveries for methyl- and inorganic Hg were quantitative over the 4 month period while ethyl-Hg species appeared to be stable for up to 2 months.     

Model reactions for abiotic mercury(II) methylation: Kinetics of methylation of mercury(II) by mono-, di-, and tri-methyltin in seawater

The usual presence of mercury(II) with monodi-, and tri-methyltin in water, sediments, and plants in estuarine environments suggests possible abiotic formation of methylmercury via methyl transfer from methyltin compounds. Kinetics studies of reactions between mercury(II) and methyltin compounds under pseudo-first-order conditions in seawater show that relative rate of methylmercury formation under the same conditions are: monomethyltin <trimethyltin> dimethyltin. This order is explainable mainly by the speciation and charge of methyltin compounds in seawater and by the existence of mercury(II) as a tetrachloro anion. A factorial experiment with the variables pH and salinity (seawater diluted with deionized water) showed that pH, but not salinity, is significant at the 95% confidence level; and that reaction rates increase as pH increases. These results suggest the possibility of abiotic methylation of mercury(II) in seawater. Additional experiments in seawater demonstrated an absence of methylation of mercury(II) (14 days) and mercury(0) (35 days) by methyl iodide.     

Low-density solvent-based dispersive liquid-liquid microextraction followed by HPLC-ICP-MS for speciation analysis of phenylarsenics in lake water

A simple and fast method of low-density solvent based dispersive liquid-liquid microextraction (LDS-DLLME) followed by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) has been developed for the speciation analysis of organoarsenic and inorganic arsenic in water samples. The low-density solvent (octanol) was given as the organic phase and injected into the aqueous sample (donor phase) with methanol as the disperser. With As (V), As (III), p-APAA, 4-HPAA, ROX and PAA as target species, factors of LDS-DLLME including pH value, anionic carriers, elution conditions and extractant, were studied in detail. Besides, volumes of solvents were further optimised by response surface methodology. Under the optimal conditions, the limits of detection for four phenylarsenics and arsenate were in the range of 0.001–0.039 μg L^?1. The relative standard deviations (RSDs) were 3.6–9.4% and the enrichment factors varied from 6.2 to 70.8. The proposed method of LDS-DLLME-HPLC-ICP-MS was satisfactorily applied to the determination of six arsenic compounds in water samples with recoveries of 81.8–111.7% for the spiked lake water samples.     

Determination of Hg(II) and Methylmercury by Electrothermal Atomic Absorption Spectrometry after Dispersive Solid-Phase Microextraction with a Graphene Oxide Magnetic Material

The toxicity of all species of mercury makes it necessary to implement analytical procedures capable of quantifying the different forms this element presents in the environment, even at very low concentrations. In addition, due to the assorted environmental and health consequences caused by each mercury species, it is desirable that the procedures are able to distinguish these forms. In nature, mercury is mainly found as Hg⁰, Hg²⁺ and methylmercury (MeHg), with the latter being rapidly assimilated by living organisms in the aquatic environment and biomagnified through the food chain. In this work, a dispersive solid-phase microextraction of Hg²⁺ and MeHg is proposed using as the adsorbent a magnetic hybrid material formed by graphene oxide and ferrite (Fe₃O₄@GO), along with a subsequent determination by electrothermal atomic absorption spectrometry (ETAAS). On the one hand, when dithizone at a pH = 5 is used as an auxiliary agent, both Hg(II) and MeHg are retained on the adsorbent. Next, for the determination of both species, the solid collected by the means of a magnet is suspended in a mixture of 50 µL of HNO₃ (8% v/v) and 50 µL of H₂O₂ at 30% v/v by heating for 10 min in an ultrasound thermostatic bath at 80 °C. On the other hand, when the sample is set at a pH = 9, Hg(II) and MeHg are also retained, but if the solid collected is washed with N-acetyl-L-cysteine only, then the Hg(II) remains on the adsorbent, and can be determined as indicated above. The proposed procedure exhibits an enrichment factor of 49 and the determination presents a linear range between 0.1 and 10 µg L⁻¹ of mercury. The procedure has been applied to the determination of mercury in water samples from different sources.     

Approach for rapid extraction and speciation of mercury using a microtip ultrasonic probe followed by LC-ICP-MS

A fast method for mercury extraction from biological samples based on the use of HCl leaching plus different enzymatic hydrolysis (with and without mercury complexing agents), and the use of focussed ultrasounds (2-mm microtip) is here proposed. Total mercury content in several biological samples was determined by FI-ICP-MS using a carrier solution consisting of 0.1% (v/v) HCl, 0.1% (v/v) 2-mercaptoethanol, to avoid memory effect, and 0.15% (w/v) KCl. For mercury speciation a RP18 chromatographic column coupled to ICP-MS was used. A mobile phase consisting of 0.1% (v/v) formic acid, 0.1% (v/v) HFBA, 2% (v/v) methanol, and 0.02% (w/v) mM l-cysteine at pH 2.1 was used for chromatographic separation of the mercury species in the sample extracts. Extraction procedures were validated by using 50 mg of tuna fish tissue CRM-463 (2.85 ± 0.16 mg kg⁻¹ for methylmercury). The recoveries obtained were 99 ± 3% and 93 ± 1% after acid leaching (HCl 7 M) and enzymatic extraction (15 mg protease type XIV in 2.5% (v/v) 2-mercaptoethanol), respectively. The optimal sonication conditions (5 min of exposure time and 40% of ultrasound amplitude) were applied to 5 mg of CRM-463 (88 ± 5%), 5 mg of mussel tissue (81 ± 11%) and to 2 mg of zebra fish embryos (90 ± 10%) obtaining good recoveries in all cases. Methylmecury was found to be the most abundant Hg specie in all samples. The developed method is simple and rapid (5 min sample treatment); it is suitable for very small samples and does not alter the original form of the mercury species. Thus, it is of special interest in those cases in which validation of the results may often be hampered by lack of sample availability.     

The use of Nafion-coated thin mercury film electrodes for the determination of the dissolved copper speciation in estuarine water

Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L₁-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu²⁺] in the San Francisco Bay estuary.     

A new potentiometric sensor based on a high-performance composite for nanomolar determination of mercury (II) in environmental samples

A new potentiometric sensor for the rapid determination of Hg²⁺ based on modified carbon paste electrode consisting of room temperature ionic liquid, 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), multi-walled carbon nanotubes (MWCNTs), alumina nanoparticles and a synthetic macrocyclic diamide ‘7,10,13-triaza-1-thia-4,16-dioxa-6,14-dioxo-2,3;17,18-dinaphtho-cyclooctadecane’ as an efficient ionophore was constructed. Prepared composite is an ideal paste because it has low drift of potential, high selectivity and fast response time (10 s), which leads to a more stable potential signal. The morphology and properties of electrodes surface were characterised by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy. A linear dynamic range of 2.01–2.01 × 10⁷ µg L^?1 with detection limit of 1.40 µg L^?1 Hg²⁺ was obtained at pH range of 2.5 to 4.5. The prepared modified electrode shows several advantages such as simple preparation method, high stability of the composite paste, high sensitivity, long-term life time (at least 13 weeks) and remarkable potentiometric reproducibility. The modified electrode was successfully applied for the accurate determination of trace amounts of Hg ²⁺ in environmental samples.     

Determination of organic and inorganic mercury species in water and sediment samples by HPLC on-line coupled with ICP-MS

This paper describes a preconcentration method for Hg²⁺ and MeHg⁺ in water samples using sodium diethyldithiocarbamate immobilized in polyurethane foam (PU-NaDDC) and an extraction method for several mercury species in sediment samples, including MeHg⁺, EtHg⁺ and PhHg⁺, which is simple, rapid, and uses a single organic solvent. Separation and measurement were done by high-performance liquid chromatography on-line with inductively coupled plasma mass spectrometry (HPLC/ICP-MS). Initially, the test of recovery was applied using procedures compatible with HPLC. Under the optimum extraction conditions, recoveries of 96.7, 96.3 and 97.3% were obtained for MeHg⁺, EtHg⁺, and PhHg⁺, respectively, from n = 4 spiked sediment samples. This study also demonstrates that the combination of solid-phase extraction on PU-NaDDC with HPLC separation and ICP-MS detection is an effective preconcentration procedure for simultaneous measurement of Hg²⁺ and MeHg⁺ at ultra-trace levels in water samples. The application of the proposed procedure to the determination of mercury species in drinking water sample was investigated. The proposed method clearly gave satisfactory average recoveries between 93.7 and 101.5%.     

Coupling of microwave induced plasma optical emission spectrometry with HPLC separation for speciation analysis of Cr(III)/Cr(VI)

Feasibility and limitations of direct coupling of high performance liquid chromatographic (HPLC) separation to microwave induced plasma (MIP)-optical emission spectrometry (OES) for elementspecific detection was tested and compared to inductively coupled plasma (ICP)-optical emission spectrometric detection on the basis of the Cr(III)/Cr(VI) speciation analysis of water samples. Coupling was performed by a hydraulic high pressure nebulizer (HHPN) radiative-heating/watercooling interface which provides about 20 % and 80 % aerosol yield in the case of helium and argon carrier gases, respectively. Desolvation efficiency of aqueous solutions was approximately 80 %. Applying the ion-pair HPLC separation, the organic eluents and reagents in the MIP cause a 50–75 % signal suppression for Cr(VI) and 25–50 % for Cr(III). In a pure aqueous solution the MIP Cr(VI) signal was by 20 % lower than that of Cr(III). These effects were lower using the ICP source, but they cannot be neglected. Easily ionizable matrix elements (Na, Ca) can cause 70 % signal suppression in the MIP, and 20 % in the ICP. Therefore, species dependent calibration is required in both cases. In the case of HPLC detection by MIP-OES, the detection limit was 13 ng for Cr(III), and 18 ng for Cr(VI). Using the ICP-OES detection, the detection limit was 0.2 ng for Cr (III) and 0.4 ng for Cr (VI). The linear dynamic ranges in both cases were two orders of magnitude. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Mercury speciation in hair by headspace injection-gas chromatography-atomic fluorescence spectrometry (methylmercury) and combustion-atomic absorption spectrometry (total Hg)

The speciation of Hg in human hair was carried out with combustion-atomic absorption spectrometry for total Hg (THg) and headspace-gas chromatography-atomic fluorescence spectrometry (HS-GC-AFS) for methylmercury (MMHg).The determination of total Hg in hair was carried out with the AMA analyzer (Advanced Mercury Analyser 254). Accuracy and reproducibility were assessed on a Certified Reference hair sample (IAEA-086 CRM), yielding, respectively, a recovery of 97.5% and a RSD of 3.2%. Analyses of 10 blank measurements resulted in a detection limit of 1.5 ng g⁻¹ of THg for a 20 mg sample of human hair.MMHg concentrations in hair were assessed with HS-GC-AFS in a single analysis step. Either acid or alkaline extraction can be applied because they yielded very similar results on a IAEA-086 CRM: we observed a recovery of 103% and a RSD of 7% with acid extraction and a recovery of 110% and a RSD of 9% with alkaline extraction. Optimization of the headspace vial, injection and GC parameters is described. The detection limit of the MMHg determination in human hair, which amounts to 0.04 ng g⁻¹ for a 20 mg sample, is far below the concentrations observed in natural samples.The number of samples that can be analyzed per hour, respectively, amounts to 8 for THg and 4 for MMHg. Finally, Hg speciation in natural human hair samples was carried out by combining both AMA and HS-GC-AFS analysis methods. THg levels were at the μg g⁻¹, level, with an average MMHg fraction of about 70%.     

On-line speciation and determination of Cr(III) and Cr(VI) in drinking and waste water samples by reversed-phase high performance liquid chromatography coupled with atomic absorption spectrometry

A simple, rapid, and selective on-line method for the speciation and determination of Cr(III) and Cr(VI) in aqueous solutions by ion-pairing HPLC coupled with flame atomic absorption spectrometry (FAAS) is described. The composition of the mobile phase has been optimized for better separation. The effects of column temperature, volume of injection loop, fuel flow rate of FAAS, and nebulizer suction rate of FAAS have also been investigated. Separation is accomplished in almost 2.5 min on a 25 cm length C18 column at 40 degrees C. The selectivity of the method has been established by investigating the effect of interfering elements on chromium determination. The detection limit (3sigma) achieved by the method was calculated as 3.7 ng/mL for Cr(III) and 2.0 ng/mL for Cr(VI). The proposed method has been validated by analyzing certified reference material (BCR 544) and successfully applied to the analysis of drinking water and wastewater samples with a relative error below 6%.