Preconcentration Of Hg Research Articles

Continuous Flow-Double Purge and Trap Method for Preconcentrating Mercury in Large Volumes of Seawater for Stable Isotope Analysis.

Mercury (Hg) isotopes provide a useful tool to understand Hg sources and processes in the environment. The Hg isotopic composition of seawater remains poorly constrained due to the lack of an efficient method to process large volumes of low-Hg-concentration seawater samples. Here, we develop a continuous flow-double purge and trap device for the in situ preconcentration of Hg in seawater. This method yielded a good Hg recovery of 91.7 ± 3.3% (n = 4, 1SD) for spiked seawater samples and gave reasonably similar Hg isotope ratios of NIST 8610, indicating a limited matrix effect and limited Hg isotope fractionation during processing of seawater. NIST 8610 δ202Hg (-0.55 ± 0.09‰, n = 4, 1SD) and Δ199Hg (0.07 ± 0.02‰, n = 4, 1SD) were similar to previously published data. The method was successfully applied to seawater collected from the Xiamen Bay and the South China Sea. The seawater samples showed a Hg recovery of 91.6 ± 5.4% (n = 12, 1SD). Seawater Δ199Hg (-0.04 ± 0.05‰, n = 7, 1SD) in the Xiamen Bay was different from seawater Δ199Hg (0.05 ± 0.07‰, n = 5, 1SD) in the South China Sea, which implies distinct Hg sources to coastal and open ocean areas and highlights the robustness of our method in understanding the Hg isotopic composition of seawater.

Optimization of a pre-concentration method for the analysis of mercury isotopes in low-concentration foliar samples.

Hg isotope analysis in samples from background regions is constrained by the presence of low Hg concentration and therefore requires a pre-concentration method. Existing Hg pre-concentration methods are constrained by long sample processing time and limited sample loading capacity. Using foliar samples as a test case, an optimized Hg pre-concentration method is presented that involves the microwave-assisted digestion of samples for Hg isotope analysis with the addition of a pre-digestion step. Microwave-digested foliar samples and CRMs were transferred to an impinger, reduced with SnCl2, and collected in a 2.25 mL concentrated inverse aqua regia (3:1 HNO3:HCl, v/v). This resulted in an optimal acid concentration in the solution ideal for analysis on MC-ICP-MS. The time for purging with Hg-free N2 was optimized to 30 min and the efficiency of the pre-concentration method was tested using a combination of approaches. Tests performed on pure reagents and matrix of foliar samples spiked with 197Hg radiotracer showed recoveries averaging 99 ± 1.7% and 100 ± 3.0%, respectively. Mercury at concentrations as low as 1.83 ng g-1 was pre-concentrated by digesting aliquots of foliage samples in individual digestion vessels. Recoveries following their pre-concentration averaged 99 ± 6.0%, whereas recoveries of 95 ± 4.7% and 95 ± 2.5% were achieved for NIST SRM 1575a (pine needle) and reagents spiked with NIST SRM 3133, respectively. Analysis using multicollector-ICP-MS showed low fractionation of δ202Hg during sample pre-concentration with no significant mass-independent fractionation. The proposed method is a relatively simple and robust way to prepare Hg samples for Hg isotopic analysis and is suitable even for complex biological matrices.

Electrochemical sensing of Hg(ii) in chicken liver and snail shell extract samples using novel modified SDA/MWCNT electrodes.

Heavy metal ions (Hg(ii)) were detected in fresh chicken liver and snail shell extract samples using novel synthesised SDA/MWCNT-modified electrodes. The synthesized N,N'-bis(salicylaldehyde)-1,2-diaminobenzene (SDA) ligand was characterized via FT-IR, 1H-NMR, and 13C-NMR spectroscopy. The hydroxyl and imine functional groups present in SDA act as active sites and bind to the MWCNT surface. The surface morphology of the modified SDA/MWCNT electrode exhibited a star-like crystal structure and the preconcentration of Hg(ii)-SDA/MWCNTs lead to a crystal cloud structure, as characterized by SEM with EDX. The enhancement of current and conductance of the SDA/MWCNT- and MWCNT-modified electrode was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The conductance (σ) values for the MWCNT- and SDA/MWCNT-modified electrodes are 234.1 × 10-5 S cm-1 and 358.4 × 10-5 S cm-1, respectively, as determined by electrochemical impedance spectroscopy. Consequently, an electrochemical sensor with outstanding performance in terms of reproducibility, stability and anti-interference ability was fabricated. The stripping analysis of Hg(ii) was performed using square wave anodic stripping voltammetry (SWASV) and cyclic voltammetry (CV). Using SWASV, a linear range of Hg(ii) response was found to be 1.3 to 158 μg L-1, and the limit of detection (LOD) was 0.24 μg L-1. Finally, the results of the recovered value of Hg(ii) in freshly prepared chicken liver and snail shell extract samples by SWASV were compared with the atomic absorption spectroscopy (AAS) results.

Mercury isotope variation during organic matter maturation to petroleum

Although both sedimentary rocks and petroleum generally contain detectable levels of Hg, the characteristics of Hg isotope fractionation and its transformation from biomass to sedimentary rocks to petroleum have not been sufficiently investigated to date. Here, we report Hg contents and isotope compositions in source rocks and crude oils from the Paleogene of the Bohai Bay Basin and in source rocks from the Permian and Jurassic of the Sichuan Basin in China. Our analysis made use of an improved crude oil Hg pre-concentration system involving pyrolytic cracking and KMnO4/H2SO4 Hg trapping to analyze Hg fractionation during organic matter maturation to petroleum. Positive mass-independent fractionation (MIF) signatures of Hg isotopes were detected in the source rocks, with Δ199Hg ranging between −0.04‰ and + 0.48‰ (mean + 0.12 ± 0.12‰), which is significantly different from the negative Δ199Hg of terrestrial non-source rocks. Positive Hg-MIF signatures were detected in the crude oil, with Δ199Hg ranging between +0.04‰ and + 0.21‰ (mean + 0.13 ± 0.06‰). We propose a model of Hg isotopic fractionation related to organic matter history. From organic matter to source rock, Hg system variations are attributed to endogenic (i.e., photoreduction) and exogenic processes (i.e., terrestrial, magmatic and hydrothermal Hg inputs). From source rock to petroleum, Hg is mobilized during hydrocarbon migration, a process that occurs with MDF but without significant MIF.

Recruiting chemical grafting method for surface modification of stainless steel to fabricate a selective sorbent for solid phase microextraction of mercury metal ion.

Keeping selectiveness and efficiency in view with solid-phase microextraction (SPME) of metal ions, this work was aimed at synthesis of a novel modified sorbent on a stainless-steel surface to fabricate a selective and efficient fiber for SPME of mercury ions from real food and biological samples. After the confirmation of sorbent structure grafted on the stainless-steel surface, by different techniques, the synthesized fiber was utilized for extraction and preconcentration of mercury before its measurement by an inductively coupled plasma-optical emission spectroscopy (ICP-OES). For optimizing the efficiency, the influences of various factors on the extraction of Hg (II) ion were scrutinized. The optimized values used for extraction were pH 7.0, adsorption time 8min, desorption time 5min, 5mL of eluent solvent containing nitric acid with concentration of 0.5mol L-1, and stirring rate of 300rpm. Underneath optimum condition, the relative standard deviation for 30 extractions, done by one synthesized fiber, was calculated to be 2.89% and for five extractions, done by 5 synthesized fibers, was calculated to be 1.78%. The high performance of the synthesized fiber was checked with high recoveries obtained from 30 successive sorption-desorption cycles, using a unique synthesized fiber. Finally, the suggested procedure was triumphally exploited for extraction and pre-concentration of Hg (II) ion in real food and biological samples.

An easy and green amine-based microextraction strategy combined UV–Vis spectrophotometric detection for mercury in natural water samples

An amine-based microextraction method was established for preconcentration of mercury by forming a 1-(2-pyridylazo)-2-naphthol (PAN) chelate complex. The Hg (II)-PAN hydrophobic complex was extracted into the N,N-dimethyl-n-octylamine phase at pH 9.5, after the pre-concentration of Hg (II), the absorption spectrum was taken with UV–Vis spectrophotometer at 555.0 nm. The effects of important analytical parameters such as pH, PAN amount, N,N-dimethyl-n-octylamine volume, sample volume and matrix effects for quantitative recovery were investigated and optimized. 0.05% (w/v) PAN volume, N,N-dimethyl-n-octylamine volume, vortex time and centrifugation time were optimized as 0.4 mL, 0.1 mL, 1 min and 15 min, respectively. The validity of the developed liquid phase micro-extraction method was checked by standard addition-recovery experiments. The presented microextraction method was successfully applied for mercury determination in natural water samples. The mercury concentration in natural water samples ranged from 0.20 to 1.42 µg mL-1. The limit of detection (LOD), limit of quantification (LOQ) and preconcentration factor (PF) were found as 0.035 μg L−1, 0.12 μg L−1 and 26.67, respectively.

Photoactive Titanium Dioxide Films with Embedded Gold Nanoparticles for Quantitative Determination of Mercury Traces in Humic Matter-Containing Freshwaters

Mercury detection in humic matter-containing natural waters is often associated with environmental harmful substances for sample preparation. Herein we report an approach based on photoactive titanium dioxide films with embedded gold nanoparticles (AuNP@TiO2 dipstick) for chemical-free sample preparation and mercury preconcentration. For this purpose, AuNPs are immobilized onto a silicon wafer and further covered with a thin photoactive titanium dioxide layer. The AuNPs allow the preconcentration of Hg traces via amalgamation, while TiO2 acts as a protective layer and, at the same time, as a photocatalyst for UV-C radiation-based sample pretreatment. Humic matter, often present in natural waters, forms stabile complexes with Hg and so hinders its preconcentration prior to detection, causing a minor recovery. This problem is solved here by irradiation during Hg preconcentration onto the photoactive dipstick, resulting in a limit of detection as low as 0.137 ng L−1 using atomic fluorescence spectrometry (AFS). A 5 min preconcentration step is sufficient to obtain successful recovery of Hg traces from waters with up to 10 mg L−1 DOC. The feasibility of the approach was demonstrated by the determination of Hg traces in Danube river water. The results show no significant differences in comparison with standard cold vapor-atomic fluorescence spectrometry (CV-AFS) measurements of the same sample. Hence, this new AuNP@TiO2 dipstick provides a single-step sample preparation and preconcentration approach that combines sustainability with high analytical sensitivity and accuracy.

Sensitive determination of mercury by magnetic dispersive solid-phase extraction combined with flow-injection-cold vapour-graphite furnace atomic absorption spectrometry

The preconcentration of Hg through MDSPE and cold vapor (CV) resulted in an excellent LOD.

Traceable Determination of Atmospheric Mercury Using Iodinated Activated Carbon Traps

Traceable determination of atmospheric mercury (Hg) represents a major analytical problem due to low environmental concentrations. Although Hg pre-concentration on activated carbon (AC) traps is a simple method for sample collection, Hg determination is difficult due to a complex matrix that cannot be easily digested using wet chemistry. Two approaches for Hg loading on iodinated AC, the purging of elemental mercury (Hg0) and the spiking a solution of standard reference material (SRM), were used to test whether spiking SRM solution on AC can be used for the traceable determination of atmospheric mercury collected as Hg0. Mercury on AC was determined using atomic absorption spectrometry after sample combustion. The detector’s response for both loading methods was identical in a wide concentration range, indicating that the spiking of SRM on AC can, indeed, be used for the calibration of analytical systems used for the determination of atmospheric mercury. This was confirmed by the determination of Hg in a real atmospheric sample collected on an iodinated AC trap and using an SRM spiking calibration. Different ACs were compared regarding their ability to quantitatively capture Hg while having the lowest breakthrough. Use of a specific impregnating solution probably converted Hg on AC to Millon’s iodide, as estimated from the fractionation thermogram.

Anodic stripping voltammetry analysis of mercury(II) on a pyridine-Au/pyridine/glassy carbon electrode

We report the simple preparation of a pyridine (Py)-stabilized Au modified glassy carbon electrode (GCE) for high-performance anodic stripping voltammetry (ASV) analysis of Hg(II). A monolayer-scale ultrathin Py film was covalently modified on a GCE by electroreduction of 4-cyanopyridine (cPy) in 0.1 M aqueous H2SO4 (Py/GCE), and then the electroreduction of a synthesized cPy-Au(III) complex generated a Py-Au nanocomposite on the Py/GCE surface (Py-Au/Py/GCE). It was found that the electrogenerated Au(0) can catalyze the electroreduction of cPy. The materials and electrodes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The gold sites on Py-Au/Py/GCE are highly active and well protected by the Py groups, and the Au-Hg amalgamation effect and the Py-Hg2+ coordination effect can make the cathodic preconcentration of Hg highly efficient, thus the Py-Au/Py/GCE offers very high sensitivity and stability for ASV analysis of Hg(II), giving a limit of detection of 12 ppt (S/N = 3). The Py-Au/Py/GCE was used for Hg(II) analysis in real water samples with satisfactory results.

Novel thionin-functionalised core shell magnetic nanoparticles for dispersive solid-phase extraction of Hg(II) in food and water samples

ABSTRACTTo develop an accurate and precise method for separation and pre-concentration of Hg(II), a novel thionin functionalised core shell structure magnetic material has been prepared and characterised. The extraction ability of the material was evaluated by magnetic solid-phase extraction coupled with inductively coupled plasma mass spectrometry determination of Hg(II) in food and water samples. Combining the advantages of magnetic separation with selective extraction of thionin towards Hg(II), the material exhibits enhanced enrich selectivity and efficiency for Hg(II). The experimental parameters influencing Hg(II) extraction efficiency, including pH of the aqueous solution, the dosage of the adsorbent, extraction time and sample volume, were systematically investigated. Under the optimised conditions, concentration of Hg(II) at 1.0 μg L−1 can be successfully enriched by the material without the interference of the common co-existing ions. The enrichment factor and adsorption capacity were 250 and 75.2 mg g−1, and precise of the method was confirmed by analysing the spiked food, water samples and standard water reference samples with the recoveries of 92.5–101.8%.

Graphene oxide as an efficient adsorbent of solid-phase extraction for online preconcentration of inorganic and organic mercurials in freshwater followed by HPLC-ICP-MS determination

For the past several decades, lots of adsorbent nanomaterials have been adopted for the enrichment of mercuric compounds. In this paper, graphene oxide bounded silica particles were employed as the absorbent for online preconcentration of Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) by solid phase extraction. The adsorbent offered satisfactory adsorption capacities of 40.7 for Hg(II), 91.4 for MeHg and 103.8 mg g−1 for EtHg. Enrichment conditions such as type, concentration and volume of conditioning and eluting reagents were optimized. The pH, volume and flow rate of sample were also optimized. High enrichment factors (1963, 1881 and 1794 for Hg(II), MeHg and EtHg, respectively) were obtained with 10 mL sample (adjusted to pH 4–7) at 10 mL min−1 flow rate, 5 μL of 10 mM benzoic acid for elution and 4 mL of 1 mM 4-phenyl-3-aminothiourea for preconditioning. The detection limits obtained were downscaled to be 0.005 for Hg(II), 0.006 for MeHg and 0.009 ng L−1 for EtHg with relative standard deviations of all the analytes below 5%. Standard reference material and spiked water samples were analyzed for validating the method with satisfactory recoveries of 89–106%. The present method was successfully applied to determine mercury compounds in drinking water, and river and tap water, in which Hg(II), MeHg and EtHg were presented below the China's drinking standard limit of 1 μg L−1.

Rapid pre-concentration of mercury in solids and water for isotopic analysis

The precise quantification of mercury (Hg) stable isotope compositions in low concentration or dilute samples poses analytical challenges due to Hg mass limitations. Common Hg pre-concentration procedures require extended processing times, making rapid Hg stable isotope measurements challenging. Here we present a modified pre-concentration method that combines commonly used Hg reduction and gold trap amalgamation followed by semi-rapid thermal desorption (less than 1 h) and chemical trapping. This custom designed system was demonstrated to perform adequately on multiple trapping matrices including a new bromine monochloride (BrCl) wet oxidant trap (40% 3HNO3:BrCl), capable of trapping consistently in 2 mL volume over a wide range of Hg masses (5–200 ng). The procedure was also shown to work effectively on natural matrices, waters and sediments, producing comparable isotope results to the direct digestion analyses. Here, we present a method that can effectively triple sample throughput in comparison to traditional procedures, and also access lower concentration matrices without compromising the accuracy or precision of Hg isotope measurements.

Mercury determination at trace levels using membrane preconcentration and benchtop total reflection X-ray fluorescence analysis

At present, there is a considerable interest in Hg monitoring in water samples due to its widespread occurrence and the high toxicity of most of its compounds. Hg determination in water samples by means of total reflection X-ray fluorescence spectrometry (TXRF) entails some difficulties due to the high vapour pressure and low boiling point of this element that produce evaporation and loss of Hg from the surface of the reflector during the drying process, commonly employed in sample preparation in TXRF analysis.In a former work we demonstrated the usefulness of PVC-based membranes functionalized with dithizone for Hg preconcentration. Limits of detection as low as 0.8 μg·L−1 Hg were obtained using a 1 kW TXRF system. The main goal of the present research was to improve the extraction system and to apply it in combination with low power TXRF instrumentation (50 W). In this sense, some extraction parameters as well as measurement conditions such as the volume of membrane deposited on the quartz reflector, the agitation speed during extraction, the aqueous sample volume and the measurement time were carefully evaluated to obtain the maximum sensitivity for Hg determination. Using the best analytical conditions, a limit of detection for Hg of 0.3 μg·L−1 was obtained which is adequate according to the limits of current legislation on the quality of water for human consumption. Additionally, a morphological study of the preconcentrated sample on the quartz reflector was performed by optical microscopy and information regarding Hg distribution along the membrane was obtained by μ-XRF analysis. It was found that Hg is not homogenously accumulated on the membrane and thus, the size of the membrane on the reflector is a critical parameter that has to be controlled to ensure the complete exposure of the loaded membrane to the X-ray beam. This fact is of special relevance when using this preconcentration approach in combination with micro-TXRF. Finally, to further prove applicability of the TXRF method for real water sample analysis, different types of spiked water samples were analysed.

An easily prepared graphene oxide–ionic liquid hybrid nanomaterial for micro-solid phase extraction and preconcentration of Hg in water samples

High retention of Hg and sensitive determination with a graphene oxide–ionic liquid hybrid nanomaterial.

PH-independent preconcentration of Hg (II) ions and rapid adsorption of methylene blue in fish and water samples by nano composite of MoS2@ MWCNT hybrid as a solid phase extraction sorbent

pH-independent preconcentration of Hg (II) ions and rapid adsorption of methylene blue in fish and water samples by nano composite of MoS2@ MWCNT hybrid as a solid phase extraction sorbent

A magnetic nanocomposite prepared from chelator-modified magnetite (Fe3O4) and HKUST-1 (MOF-199) for separation and preconcentration of mercury(II)

We describe a magnetic metal-organic framework for preconcentration of Hg(II). The material is obtained from magnetite (Fe3O4) nanoparticles that were modified with 4-(5)-imidazoledithiocarboxylic acid and then reacted with trimesic acid and Cu(II) acetate to form the metal-organic framework capable of extracting Hg(II). The sorption time, amount of the magnetic nanocomposite, and pH value of the sample were selected as the main affecting factors in sorption, and central composite design and response surface methodology were applied to optimize these parameters. Following sorption of Hg(II), the sorbent is removed by a magnet, Hg(II) is eluted with a solution of thiourea and then quantified by cold vapor AAS. The type, volume and concentration of the eluent, and the elution time were selected for the optimization of the elution. The results showed the sorption process to obey the Langmuir model. The maximum monolayer capacity is as high as 254 mg g−1, and the Langmuir constant is 0.330 L mg−1. The findings can be well described by pseudo second-order kinetics. High sorption capacity means that one needs less sorbent. Under the optimal conditions, the limit of detection and limit of quantification for Hg(II) were 10 ng L−1 and 40 ng L−1, respectively and the relative standard deviations are <8.3 %. The nanocomposite was successfully applied to the rapid extraction of trace amounts of mercury ions from fish and canned tuna samples.

Multivariate optimization, preconcentration and determination of mercury ions with (1-(p-acetyl phenyl)-3-(o-methyl benzoate)) triazene in aqueous samples using ICP-AES

Modified GO with a new triazene compound was used as an efficient adsorbent for preconcentration of Hg(ii) in water samples.

Nanogold-Decorated Silica Monoliths as Highly Efficient Solid-Phase Adsorbent for Ultratrace Mercury Analysis in Natural Waters.

We propose a novel analytical method for mercury (Hg) trace determination based on direct Hg preconcentration from aqueous solution onto a gold nanoparticle-decorated silica monolith (AuNP@SiO2). Detection of Hg is performed after thermal desorption by means of atomic fluorescence spectrometry. This new methodology benefits from reagent-free, time- and cost-saving procedure, due to most efficient solid-phase adsorbent and results in high sensitive quantification. The excellent analytical performance of the whole procedure is demonstrated by a limit of detection as low as 1.31 ng L(-1) for only one-min accumulation duration. A good reproducibility with standard deviations ≤5.4% is given. The feasibility of the approach in natural waters was confirmed by a recovery experiment in spiked seawater with a recovery rate of 101%. Moreover, the presented method was validated through reference analysis of a submarine groundwater discharge sample by cold vapor-atomic fluorescence spectrometry resulting in a very good agreement of the found values. Hence the novel method is a very promising new tool for low-level Hg monitoring in natural waters providing easy-handling on-site preconcentration, reagent-free stabilization as well as reagent-free, highly sensitive detection.

Determination of Hg(II) ions in sea food samples after extraction and preconcentration by novel Fe3O 4@SiO 2@polythiophene magnetic nanocomposite.

This work describes a novel Fe3O4@SiO2@polythiophene magnetic nanocomposite and its application in the preconcentration of Hg(II) ions. The parameters affecting the preconcentration procedure were opted by a Box-Behnken design through response surface methodology. Three factors (uptake time, magnetic nanosorbent amount, and pH of sample) were selected as the main factors affecting the sorption step, while four variables (type, volume and concentration of the eluent as well as the elution time) were selected as main factors in the optimization study of the elution step. Following the sorption and elution of Hg(II), it was quantified by cold vapor atomic absorption spectrometry. Under the optimum condition, the limit of detection was 0.02 ng mL(-1) and all the relative standard deviations were less than 9.2 %. The obtained sorption capacity of this new sorbent was 59 mg g(-1). Finally, this nanocomposite was successfully applied to the rapid extraction of trace quantities of Hg(II) ions in sea food samples and satisfactory results were obtained.