Determination of inorganic and methylmercury in fish by cold vapor atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry

Biosynthesis of bifunctional silver nanoparticles for catalytic reduction of organic pollutants and optical monitoring of mercury (II) ions using their oxidase-mimic activity

In this study, an aqueous extract of Sclerocarya birrea leaves was used as a reducing agent to synthesize silver nanoparticles (AgNPs). The synthesis was carried out at room temperature and was both rapid and simple. Different characterization techniques such as UV/visible spectroscopy, surface-enhanced Raman spectroscopy, X-ray diffraction, and focused ion beam scanning electron microscopy were used to confirm the formation of AgNPs. The synthesized nanoparticles exhibited catalytic activity for the reduction of 4-nitrophenol, methyl orange, methylene blue, and rhodamine 6G. The catalytic activity was monitored by measuring the UV/visible absorbance spectra of the compounds using sodium borohydride as a reducing agent and found to be high. Additionally, the particles displayed oxidase-like activity. In the presence of AgNPs, 3, 3', 5, 5'-tetramethylbenzidine (TMB) which is colorless was transformed to oxidized TMB, which is blue, using dissolved oxygen as the oxidant. In the presence of Hg2+, the oxidase-like activity was enhanced. On the basis of this observation, an assay for the analysis of Hg2+ was developed. The linear range of the calibration curve is wide (0-600 µM) and the limit of detection (LOD) is low, as small as 34.8 nM. The method is strongly selective towards Hg2+. Tap water obtained from the laboratory where these experiments were carried out was used to study the feasibility of the method in real sample analyses.

Quantitative Visual Detection of Mercury Ions With Ratiometric Fluorescent Test Paper Sensor

A novel ratiometric fluorescence probe based on nitrogen-doped blue carbon dots (NCDs) and red gold nanoclusters (Au NCs) for mercuric ion (Hg2+) has been prepared and characterized. A user friendly fluorescent test paper based sensor combined with smartphone was fabricated for rapid visual and quantitative detection. Hg²⁺ can specifically bind to Au⁺ on the surface of Au NCs, leading to the quench of red fluorescence while the fluorescence intensity of the NCDs with blue fluorescence remained unchanged as a internal standard signal. The implement of paper-based sensor address some common drawback in analytical process such as the detection time, analysis cost. In a further demonstration, a homemade detection device with smartphone was used to qualify the Hg²⁺. After adding different concentration of Hg²⁺, red, purple, and blue colors were obtained on the detection zones of the fluorescent test paper. The Android App Color Grab was used to identify the red, green and blue (RGB) values of fluorescent color. The rapid visual and quantitative detection of Hg²⁺ was accomplished with the detection limit of 2.7 nM for fluorescence, 25 nM for smartphone and 32 nM for paper strip. The developed multi-mode detection platform was successfully applied to the detection of mercury ions in water samples with acceptable recoveries. The NCDs and Au NCs probe facilitate the one-site environmental monitoring for Hg²⁺ with “naked-eye” and smartphone.

Understanding the effects of sulfur input on mercury methylation in rice paddy soils

Sulfur could be introduced into paddy soils via dry or wet deposition, irrigation, and fertilization, which subsequently impacts the production of methylmercury (MeHg), a bioaccumulative neurotoxicant. However, effects of sulfur input on MeHg production are variable, possibly due to the multiple effects of sulfur on Hg mobility and/or microbial Hg methylators, leading to uncertainties in predicting MeHg risk. To address that, we explored the effects of different types and amounts of sulfur as well as concentrations of ambient sulfate on Hg methylation in paddy soils, and elucidated the mechanisms by quantifying changes in (1) Hg mobility and (2) microbial Hg methylators (e.g., sulfate-reducing bacteria, SRB). Our results indicated that MeHg levels increased by 40-86% and 30-96% in soils under various types (i.e., 200 mg kg^-1 elemental sulfur, ammonium sulfate, sulfur-coated urea and potassium sulfate (K₂SO₄)) and different amounts (i.e., 100, 200 and 400 mg kg^-1 K₂SO₄) of sulfur input. The enhanced MeHg production could be explained by increased Hg mobility but not changes in microbial Hg methylators. Besides, sulfate input increased MeHg levels (89-240%) in soils with low ambient sulfate levels (<100 mg kg^-1) but had no effect on high-sulfate soils (>380 mg kg^-1). These could be explained by the diverse responses of Hg mobility and microbial Hg methylators to sulfate input at different ambient sulfate levels. Our study opens the "black box" of Hg methylation under sulfur input, which would help reduce uncertainties in predicting MeHg risk in soils.

Determination of Total Mercury in Solid Samples by Anodic Stripping Voltammetry

The anodic stripping voltammetry (ASV) was investigated to determine total mercury in solid samples using a gold electrode. The mercury was deposited on the gold electrode in a preconcentration step. The oxidation peak of mercury was irreversible. The optimal conditions of the procedure were found to be as follows: 0.05 mol L−1 HCl solution, deposition potential −0.5 V vs. Ag/AgCl/KCls, deposition time 40 s, and sweep rate 0.04 V s−1. Under the optimal conditions, the peak current showed a linear dependence on Hg2+ concentration in the range from 0.01 to 0.1 mg l−1. The detection limit and quantification limit were 4.28 µg L−1 and 12.98 µg L−1, respectively. The mean recovery and relative standard deviation were 91.2% and 2.4% (n = 9). The procedure was successfully applied for determining total mercury in samples collected from Hanoi light bulb warehouse—The Rang Dong Light Source and Vacuum Flask JSC. The results were compared with cold vapor atomic absorption spectrometry (CV-AAS).

Photo-generation of mercury cold vapor mediated by graphene quantum dots/TiO2 nanocomposite: On line time-resolved speciation at ultra-trace levels

Mercury speciation was achieved using a nanocomposite, consisting of graphene quantum dots (GQDs) and TiO₂ nanoparticles, to mediate photo-degradation of mercurial species into the Hg cold vapor detected by atomic spectrometry. Sample solution (containing Hg²⁺, CH₃CH₂Hg, and CH₃Hg at hundreds of ng L^-1) was placed in quartz tube containing formic acid solution (2% v/v) and microliter aliquot of GQDs/TiO₂ nanocomposite dispersion (0.6 mg of nanocomposite). The tube was placed inside a photochemical reactor then, adapted to the mercury-dedicated spectrometer. Quantitative speciation was achieved taking advantage of the differences in UV photodegradation kinetics: Hg²⁺ (5 min), CH₃CH₂Hg (9 min) and CH₃Hg (13 min). Gas-chromatography cold vapor atomic fluorescence spectrometry was used to confirm the evolution of the reactions over time during photo-reaction. The limits of detection were 10 ng L^-1 for CH₃CH₂Hg and 7 ng L^-1 for Hg²⁺ and CH₃Hg.

Carbon dots as rapid assays for detection of mercury(II) ions based on turn-off mode and breast milk

In this research, nitrogen co-doped carbon dots were synthesized by solid thermal method with citric acid used as the precursor of carbon, and melamine as nitrogen source. Such carbon dots show high quantum yield of 44%. Furthermore, the native fluorescence of CDs can be reduced by mercury(II), while other metals had no significant influence on fluorescence intensity. During the study, the optimal parameters were selected, such as pH or time for incubation with analyte. Under the optimal conditions, quenching effect caused by mercury ions was evaluated. It was observed that with increasing mercury concentration, the fluorescence of the carbon dots decreased proportionally. The response was characterized by linearity within the range from 2 to 14 μM. Moreover, the limit of detection was 0.44 μM. It was the first time that human milk was used as a real sample to test the applicability of carbon dots. The study results demonstrated good recovery in the 74-111% range (RSD < 6%) As a novel carbon material, CDs show promise for broader applications in analyzing complicated biological samples.

Interference-free, green microanalytical method for total mercury and methylmercury determination in biological and environmental samples using small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry

An analytical method for the quantification of total Hg and CH₃Hg⁺ in biological tissues (fish, mushroom) and water sediment was developed based on small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry using a low-resolution microspectrometer as detector. Sample preparation was carried out according to the procedure recommended by JRC Technical Report of European Commission for the determination of CH₃Hg⁺ in seafood and adapted by us for lower consumption of reagents. Amounts of 0.1 - 0.5 g sample were subjected to extraction in 5 ml of 47% HBr then CH₃Hg⁺ was extracted in 2 × 1 ml toluene and back-extracted in 2 ml aqueous solution of 1% l-cysteine. Total Hg/CH₃Hg⁺ were quantified in 10 μl of acidic extract/l-cysteine solution after electrothermal vaporization and measurement of 253.652 nm Hg signal in the episodic emission spectra. Under the optimal working conditions of system (70 °C sample drying, 1300 °C sample vaporization, 10 W plasma power and 150 ml min^-1 Ar flow) the limits of detection were 7.0 μg kg^-1 total Hg and 3.5 μg kg^-1 CH₃Hg⁺. Comparison of slopes in external calibration and standard addition procedure revealed the lack of non-spectral interferences of multimineral matrix, so that the calibration against Hg²⁺ standards was adopted. Pooled recovery of total mercury/methylmercury was 101 ± 7%/100 ± 7%, while precision assessed from measurements of real samples was in the range 1.6-9.6%/2.7-12.8%. The proposed method validated according to Eurachem Guide 2014 is selective and complies with demands in European legislation (Decisions 657/2002; 333/2007; 836/2011) and Association of Official Analytical Chemists Guide in terms of performances for food control. The method displays a high degree of greenness by circumventing cold vapor generation, use of small amounts of reagents and full-miniaturized instrumentation resulting in low analytical costs without reducing results quality. Besides, the method is simple and rapid, since it uses external calibration curves prepared from Hg²⁺standard solutions both for total Hg and CH₃Hg⁺ determination.

Visual and fluorescent detection of mercury ions using a dual-emission ratiometric fluorescence nanomixture of carbon dots cooperating with gold nanoclusters

Mercury (II) ions (Hg²⁺), as one of the most toxic heavy metals, can cause irreversible damage to human health even at very low concentration due to its high toxicity and bioaccumulation. Herein, a facile ratiometric fluorescence nanomixture based on carbon dots‑gold nanoclusters (CDs-Au NCs) was constructed for quantitative detection of Hg²⁺. Lysine functionalized carbon dots (CDs) were prepared by one-pot hydrothermal method, while gold nanoclusters (Au NCs) were synthesized via using chicken egg white (CEW) as reducer and stabilizer. The novel nanomixture exhibited two strong emission peaks at 450 nm and 665 nm under 390 nm excitation, and showed pink fluorescence under UV light. Interestingly, the fluorescence of the CDs-Au NCs nanomixture was selectively response to Hg²⁺. The fluorescence of Au NCs at 665 nm was decreased when Hg²⁺ was presented in the solution, while the fluorescence of CDs at 450 nm stayed constant. The fluorescence color changed from pink to blue obviously with increasing the concentration of Hg²⁺, which indicated that CDs-Au NCs could be used for visual detection Hg²⁺ by the naked eye. Under optimal conditions, this ratiometric fluorescent sensor could detect Hg²⁺ accurately and possess a great sensitivity with a detection limit of 63 nM. In addition, this method was applied to detect Hg²⁺ in real water samples with great recoveries, suggesting its potential in practical application with simplicity, environmentally friendly and low cost.

Speciation Analysis of Trace Mercury in Sea Cucumber Species of Apostichopus japonicus Using High-Performance Liquid Chromatography Conjunction With Inductively Coupled Plasma Mass Spectrometry

In this paper, a simple and cost-effective method using high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry with a rapid ultrasound-assisted extraction was used for analysis speciation of trace mercury in sea cucumber species of Apostichopus japonicus. The effective separation of inorganic mercury, methylmercury, and ethylmercury was achieved within 10 min using Agilent ZORBAX SB-C₁₈ analytical and guard columns with an isocratic mobile phase consisting of 8% methanol and 92% H₂O containing 0.12% L-cysteine (m/v) and 0.01 mol/L ammonium acetate. Mercury species were extracted from A. japonicus samples using a solution containing 2-mercaptoethanol, L-cysteine, and hydrochloric acid and sonicating for 0.5 h. The limits of detection of inorganic mercury, methylmercury, and ethylmercury were 0.12, 0.08, and 0.20 μg/L, and the minimum detectable concentrations (measured at 0.500 g sample volume in 10.00 mL) were 2.4, 1.6, and 4.0 μg/kg, respectively. Analysis of a scallop certified reference material (GBW 10024) revealed accordance between the experimental and certified values. This study provides a reference for the evaluation of mercury speciation in sea cucumber and other seafood.

Facile Ag-Film Based Surface Enhanced Raman Spectroscopy Using DNA Molecular Switch for Ultra-Sensitive Mercury Ions Detection

Heavy metal pollution has long been the focus of attention because of its serious threat to human health and the environment. Surface enhanced Raman spectroscopy (SERS) has shown great potential for metal detection owing to many advantages, including, requiring fewer samples, its minimal damage to specimen, and its high sensitivity. In this work, we proposed a simple and distinctive method, based on SERS, using facile silver film (Ag-film) combined with a DNA molecular switch, which allowed for the highly specific detection of heavy metal mercury ions (Hg²⁺). When in the presence of Hg²⁺ ions, the signals from Raman probes attach to single-stranded DNA, which will be dramatically enhanced due to the specific structural change of DNA strands-resulting from the interaction between Hg²⁺ ions and DNA bases. This SERS sensor could achieve an ultralow limit of detection (1.35 × 10^-15 M) for Hg²⁺ detection. In addition, we applied this SERS sensor to detect Hg²⁺ in real blood samples. The results suggested that this SERS platform could be a promising alternative tool for Hg²⁺ detection in clinical, environmental, and food inspection.

Methylmercury determination in seafood by photochemical vapor generation capacitively coupled plasma microtorch optical emission spectrometry

A non-chromatographic method based on double liquid-liquid extraction and measurements by UV photochemical vapor generation capacitively coupled plasma microtorch optical emission spectrometry was developed and characterized for methylmercury determination in seafood. Samples were prepared following the procedure recommended in JRC Technical Report of European Commission formerly proposed for the determination of methylmercury in seafood by thermal decomposition atomic absorption spectrometry, namely confinement of Hg species in 47% HBr solution, extraction of CH₃Hg⁺ in toluene and back-extraction in 1% l-cysteine aqueous solution. Mercury cold vapor was generated by flow injection UV photo-reduction from CH₃Hg⁺ in 0.6molL^-1 HCOOH, while quantification was performed against external Hg²⁺ aqueous standards and measuring Hg 253.652nm emission using a low power/Ar consumption plasma microtorch (15W, 100mLmin^-1) and a low resolution microspectrometer (Ocean Optics). The figures of merit and analytical capability were assessed by analyzing certified reference materials and test samples of fish fillet and discussed in relation with requirements for Hg determination in seafood in European legislation (Decisions 2007/333/EC and 2002/657/EC) as well as compared to performances achieved in thermal decomposition atomic absorption spectrometry. The limit of detection and quantification of 2µgkg^-1 and 6µgkg^-1 respectively, precision of 2.7-9.4% and accuracy of 99±8% of the proposed method for the determination of CH₃Hg⁺ fulfill the demands of European legislation for Hg quantification. The limit of detection and quantification were better than those in the used reference method or other non-/chromatographic methods taken for comparison. The analysis of certified reference materials and the Bland and Altman test performed on 12 test samples confirmed trueness of the proposed method and its reliability for the determination of traces of CH₃Hg⁺ with 95% confidence level. The proposed method fulfills several demands of the eco-scale concept, is sensitive, simple and safe related to sample preparation through elimination of classical, harmful reductants and attractive by using economical miniaturized instrumentation incorporating a low power and low Ar consumption plasma.

Highly sensitive SERS sensor for mercury ions based on the catalytic reaction of mercury ion decorated Ag nanoparticles

Schematic diagram of the SERS sensing mechanism for mercury ions by a catalytic oxidation reaction.

Air pollution study in Croatia using moss biomonitoring and ICP-AES and AAS analytical techniques

Moss biomonitoring technique was applied in a heavy-metal pollution study of Croatia in 2006 when this country participated in the European moss survey for the first time. This survey was repeated in 2010, and the results are presented in this study. For this purpose, 121 moss samples were collected during summer and autumn 2010. The content of 21 elements was determined by inductively coupled plasma-atomic emission spectrometry and atomic absorption spectrometry. Principal component analyses was applied to show the association between the elements. Six factors (F1-F6) were determined, of which two are anthropogenic (F3 and F6), two are mixed geogenic-anthropogenic (F1 and F5), and two are geogenic factors (F2 and F4). Geographical distribution maps of the elements over the sampled territory were constructed using geographic information systems technology. Comparison of the median values of some of the anthropogenic elements-such as arsenic, cadmium, chromium, copper, mercury, nickel, lead, vanadium, and zinc-with those from the 2006 study shows that anthropogenic pollution has changed insignificantly during the last 5 years. The data obtained in the investigation in Norway are taken for comparison with pristine area, which indicates that Croatia is somewhat polluted but still, shows a more favourable picture when compared with two neighbouring countries.

Mercury determination in non- and biodegradable materials by cold vapor capacitively coupled plasma microtorch atomic emission spectrometry

A new analytical system consisting of a low power capacitively coupled plasma microtorch (20 W, 13.56 MHz, 150 ml min(-1) Ar) and a microspectrometer was investigated for the Hg determination in non- and biodegradable materials by cold-vapor generation, using SnCl(2) reductant, and atomic emission spectrometry. The investigated miniaturized system was used for Hg determination in recyclable plastics from electronic equipments and biodegradable materials (shopping bags of 98% biodegradable polyethylene and corn starch) with the advantages of easy operation and low analysis costs. Samples were mineralized in HNO(3)-H(2)SO(4) mixture in a high-pressure microwave system. The detection limits of 0.05 ng ml(-1) or 0.08 μg g(-1) in solid sample were compared with those reported for other analytical systems. The method precision was 1.5-9.4% for Hg levels of 1.37-13.9 mg kg(-1), while recovery in two polyethylene certified reference materials in the range 98.7 ± 4.5% (95% confidence level).