Stripping voltammetric determination of mercury(II) at antimony-coated carbon paste electrode

A new procedure was elaborated to determine mercury(II) using an anodic stripping square-wave voltammetry at the antimony film carbon paste electrode (SbF-CPE). In highly acidic medium of 1 M hydrochloric acid, voltammetric measurements can be realized in a wide potential window. Presence of cadmium(II) allows to separate peaks of Hg(II) and Sb(III) and apparently catalyses reoxidation of electrolytically accumulated mercury, thus allowing its determination at ppb levels. Calibration dependence was linear up to 100 ppb Hg with a detection limit of 1.3 ppb. Applicability of the method was tested on the real river water sample.     

Flow Injection Analysis of Mercury/Cold Vapor Atomic Fluorescence Spectrophotometry

Abstract

A new flow injection system for the determination of mercury by the cold vapor atomic fluorescence method is described. A sample solution (64 μ1) is injected into a stream of 0.1 M hydrochloric acid, which is mixed with a stream of 3% tin (II) chloride solution in a mixing joint. The combined stream is carried through a reaction coil for reduction of Hg (II) to Hg (0) and subsequently introduced into a specially designed gas-liquid separation vessel. Then the vaporized mercury is swept into a flow type fluorescence cell with a continuous flow of argon after removal of water in the gas phase through a condenser. Mercury is excited with an electrodeless discharge lamp as a source and the mercury fluorescence at both 184.9 and 253.7 nm is measured with a solar-blind photomultiplier. This method allows about 35 determinations of mercury in aqueous samples per hour. The calibration curve is linear over the 0–20 ppb range of mercury. The limit of detection (S/N = 3) is 0.008 ng (0.12 ppb × 64 μ1) and the coefficient of variation is below 1% for the 1–20 ppb solutions (n=10).     

Determination of Mercury in Geological Materials by Continuous-Flow,Cold-Vapor,Atomic Absorption Spectrophotometry

Abstract

To determine mercury in geological materials, samples are digested with nitric acid and sodium dichromate in a closed teflon vessel. After bringing to a constant weight, the digest is mixed with air and a sodium chloride-hydroxylamine hydrochloride-sulfuric acid solution and then Hg(II) is reduced to Hg with stannous chloride in a continuous flow manifold. The mercury vapor is then separated and measured using cold vapor atomic absorption spectrophotometry (CV-AAS). For a 100 mg sample the limit of detection is 20 parts per billion (ppb) Hg in sample. To obtain a 1% absorption signal, the described method requires 0.21 ppb Hg solution (equal to 16 ppb in sample). Precision is acceptable at less than 1.2% RSD for a 10 ppb Hg aqueous standard. Accuracy is demonstrated by the results of the analysis of standard reference materials. Several elements do interfere but the effect is minimal because either the digestion procedure does not dissolve them (e.g., Au or Pt) or the; are normally of low abundance (e.g., Se or Te).     

Kinetic and equilibrium studies on mercury(II)-coproporphyrin-I. Metal ion exchange reaction with cobalt(II) and application to determination of trace mercury(II)

The reaction of 3,8,13,18-tetramethyl-21H,23H-porphine-2,7,12,17-tetrapropionic acid or coproporphyrin-I (CPI) with mercury(II) was studied spectrophotometrically, and kinetic and equilibrium constants were determined; the influence of temperature on the reaction rate was also studied. It was verified that mercury(II) accelerates the incorporation reaction of cobalt(II) into CPI; the kinetics and mechanism of this reaction at high alkaline pH were studied. Sensitive kinetic methods for the determination of mercury(II) at ppb levels have been established; the apparent molar absorbivity and Sandell's sensitivity for the recommended procedure, at 368 nm, and 400 s after the start of the reaction, were: 4.23x10(5) (l mol(-1)cm(-1)) and 0.474 (ng cm(-2)) (for A=0.001).     

Application of a wool column for flow injection online preconcentration of inorganic mercury(II) and methyl mercury species prior to atomic fluorescence measurement

The use of an unmodified native sheep wool packed minicolumn for the online preconcentration of Hg(II) and methyl mercury species prior to the determination of mercury by atomic fluorescence spectrometry was investigated. Experimental conditions, such as pH, desorbing agents, volume of solution were optimized. 0.5M thioglycolic acid was found to be a successful eluting agent for both mercury species. Breakthrough and total capacities were determined. The method is simple and rapidly applicable for the determination of Hg(II) and methyl mercury in tap water. The accuracy of the method was examined by the analysis of a peach leaves standard reference material. Recoveries of spiked mercury species in tap water were 105.8% for Hg(II) and 98.8% for methyl mercury.     

Low-level mercury determination with thiamine by fluorescence optosensing

A sensitive fluorescence optosensing method for the determination of Hg(II) in water samples is described. The method, using a flow injection technique, is based on the immobilization on a non-ionic-exchanger solid support (packed in a flow cell placed in a conventional fluorimeter) of the thiochrome formed by the oxidation of thiamine with Hg(II) in a continuous flow carrier at pH 8.1. Experimental parameters such as the solid support, the carrier pH, the thiamine concentration and the flow-rate were investigated to select the optimum operating conditions. The proposed optosensor showed a relative standard deviation of + 3.0% for ten replicates analysis of 100 ng ml(-1) of mercury(II). A detection limit of 3 ng ml(-1) for mercury(II) was achieved for 4-ml sample injections. A detailed study of interferences (possible elements present in natural waters) demonstrated that this optosensing method is virtually specific for this metal, because it allows the determination of mercury in the presence of relatively large amounts of other heavy metals and compounds present in natural waters, such as Mg(II) or Ca(II). The method was successfully applied to the determination of Hg(II) in spiked samples of mineral, tap and sea water.     

An improved speciation method for mercury by GC/CVAFS after aqueous phase ethylation and room temperature precollection

An improvement has been made in previous mercury speciation methods, which omits the use of liquid nitrogen by modifying the GC conditions. In addition, the sometimes observed thermal decomposition of ethylation derivatives in the process of desorbing the compounds to the GC column has been investigated and overcome. The resulting improvements have allowed simultaneous determination of methylmercury (MMHg) and inorganic mercury (Hg(II)). They have also increased the precision of the ethylation reaction and refined the MMHg determination. Optimal conditions for MMHg were confirmed and supplemented, while the parameters for dimethyl mercury (DMHg) and Hg(II) were thoroughly investigated for the first time. The absolute detection limits (DL) for 2sigma of the reagent blanks as Hg and about 0.6, 0.6 and 1.3 pg for DMHg, MMHg and Hg(II), respectively. The improved method is five-fold faster than the original method, allowing up to 80 samples to be analyzed within 8 hr.     

Fast Spectrometric Method for Mercury(II) Determination Based on Glucose-Oxidase Inhibition

A fast spectrometric kinetic method for mercury(II) ions determination based on their property to inhibit glucose-oxidase activity is presented. The measurement of enzyme activity was based on enzymatic reduction of benzoquinone to hydroquinone and on the measurements of the initial rate of hydroquinone absorbance increase at 290 nm. A calibration curve for Hg(II) concentrations was obtained in the 0.05–1.0 μg/mL range, with a detection limit of 0.015 μg/mL and a relative standard deviation RSD ≤ 2.7%. The analysis time was 2 min. Determination of mercury in a real sample was in good agreement with the declared mercury concentration.     

A highly selective colorimetric aqueous sensor for mercury

A new colorimetric mercury sensor is reported based on binding to terpyridine derivatives. It is able to selectively detect Hg II ions over a number of environmentally relevant ions including Ca II, Pb II, Zn II, Cd II, Ni II, Cu II, and others. The response time upon exposure to Hg II is instantaneous. By the "naked eye," the detection limit of Hg II is 2 ppm (25 microM) in solution. With a spectrometer, this detection limit is increased down to 2 ppb (25 nM), which is the current EPA standard for drinking water. The significant problem of mercury poisoning requires new methods of detection that are sensitive and selective. Here we report a new simple system that takes advantage of the unique optical properties generated by terpyiridine-Hg complexes.     

Indirect determination of submicrogram amounts of sulfide by flameless atomic absorption spectrometry of mercury

Summary A rapid and simple method to determineg and sub-g amounts of sulfide has been developed. It involves the addition of a known amount of mercury(II) to the sample solution, formation of stable HgS, and determination of the residual mercury(II) in the solution by flameless atomic absorption spectrometry. The proposed method allows sulfide to be determined down to 0.2 ppb with a relative standard deviation of less than 2%.

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Zusammenfassung Ein schnelles und einfaches Verfahren zur Bestimmung von Mikrogramm und Submikrogrammengen Sulfid wurde ausgearbeitet. Es beruht auf der Zugabe einer bekannten Menge Hg(II) zur Probelösung, der Bildung von beständigem HgS und der Bestimmung des restlichen Hg(II) durch flammenlose Atomarabsorptionsspektrometrie. Die vorgeschlagene Methode erlaubt die Bestimmung von mindestens 0,2 ppb Sulfid mit einer relativen Standardabweichung von weniger als 2%.

     

Mercury speciation in environmental samples by cold vapour atomic absorption spectrometry with in situ preconcentration on a gold trap

A method has been developed for the determination of total and organic mercury in biological materials and sediments. A microwave assisted mineralization of the organic mercury, after its extraction from the matrix, is described. This procedure warrants complete transformation of Hg(II) and, consequently, the quantitative reduction to Hg(0). The conditions for mercury reduction were optimized by a central composite design. The preconcentration of the analyte has been achieved by amalgamation on a trap system, consisting in a pyrolytic graphite platform wound by a gold wire. Mercury was determined by cold vapour atomic absorption spectrometry. The method was validated by the analysis of two certified reference materials and applied to the determination of total and organic mercury species in mussel tissues and sediments. The method is simple and practical, and offers the advantage of not requiring special equipment to measure inorganic and organic mercury simultaneously.     

A Robust Electrochemical Sensor Based on Butterfly-shaped Silver Nanostructure for Concurrent Quantification of Heavy Metals in Water Samples

Heavy metals in drinking water have become a severe threat to human health. Detection of heavy metals has been achieved by electrochemical sensors that are modified with complex nanocomposites; however, reproducibility of these sensors is still a big challenge when applied in commercial settings. Here, a simple, very robust, and sensitive electrochemical sensor based on a screen-printed carbon electrode modified with butterfly-shaped silver nanostructure (AgNS/SPCE) has been developed for the concurrent determination of cadmium (II), lead (II), copper (II), and mercury (II) in water samples. The electrochemical behavior of the modified electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. The AgNS/SPCE showed distinct peak potentials and a significant increase in the peak currents for all heavy metals, attributed to the high electrical conductivity and electrocatalytic activity of the synthesized butterfly-shaped AgNS. Moreover, the excellent stability and sensitivity towards simultaneous quantification of heavy metals have been obtained with detection limits of 0.4 ppb, 2.5 ppb, 7.3 ppb, and 0.7 ppb for Cd (II), Pb (II), Cu (II), and Hg (II), respectively. Besides, the constructed sensor was successfully applied to simultaneously quantify target heavy metals in spiked water samples. Owing to excellent sensitivity, high robustness, affordability, and fast response, the presented electrochemical sensor could be incorporated into a portable and miniaturized potentiostat device, making it a promising method for on-site water analysis.     

Immobilization of DNA on magnetic microparticles for mercury enrichment and detection with flow cytometry

Mercury detection in water has attracted a lot of research interest due to its highly toxic nature and adverse environmental impact. In particular, the recent discovery of specific binding of Hg(II) to thymine-rich (T-rich) DNA resulting in T-Hg(II)-T base pairs has led to the development of a number of sensors with different signaling mechanisms. However, the majority of such sensors were non-immobilized. Immobilization, on the other hand, allows active mercury adsorption, signal amplification, and sensor regeneration. In this work, we immobilized a thymine-rich DNA on a magnetic microparticle (MMP) surface through biotin-streptavidin interactions. In the presence of Hg(II), the DNA changes from a random coil structure into a hairpin, upon which SYBR Green I binds to emit green fluorescence. Detection was carried out by using flow cytometry where the fluorescence intensity increased ≈9-fold in the presence of mercury and the binding of mercury reached equilibrium in less than 2 min. The sensor showed a unique sample-volume-dependent fluorescence signal change where a higher fluorescence was obtained with a larger sample volume, suggesting that the particles can actively adsorb Hg(II). Detection limits of 5 nM (1 ppb) and 14 nM (2.8 ppb) were achieved in pure buffer and in mercury-spiked Lake Ontario water samples, respectively.     

Determination of trace levels of mercury in water samples based on room temperature phosphorescence energy transfer

A novel method has been developed for the sensitive determination of mercury in aqueous media by room temperature phosphorescence (RTP). The measurement principle is based on the energy transfer (ET) from a phosphor molecule (acting as a donor) to a Hg-sensitive dye (acceptor). To our acknowledgment this is the first RTP method for mercury measurement developed so far. α-Bromonaphthalene (BrN) was selected as the phosphorescent donor molecule (BrN can produce significant RTP emission in aqueous media in a β-cyclodextrin rigid microenvironment without deoxygenation).The absorption spectrum of the complex formed between mercury and the dithizone dye possesses a desirable spectral overlap with the RTP emission spectrum of the donor (BrN), giving rise to a nonradiative ET from the phosphor molecules to the mercury complex. An increase in the concentration of Hg(II) causes an increase on the concentration of the dithizone complex (acceptor) with the subsequent increase of the absorbance and, therefore, resulting in a decrease of the RTP emission. Both, RTP intensities and triplet lifetimes of the BrN decreased with increases on the Hg(II) concentration.Possible interferences present in natural waters, including different cations and anions, which could affect the analytical response, were evaluated and the analytical performance characteristics investigated. The use of phosphorescence measurements (low background noise signals) resulted in an improvement on the sensitivity of the Hg(II) detection higher than five times as compared to the molecular absorption spectrophotometric method for Hg(II) detection based on dithizone as Hg-indicator. A detection limit (D.L.) of 14 ng ml⁻¹ of Hg(II) was obtained by RTP with a precision of ±4.8% for five replicates of 300 ng ml⁻¹ of Hg(II). The usefulness of the method was successfully evaluated by the determination of Hg(II) in spiked natural water samples.     

Off-line combination of RPHPLC and Trace Mercury Analyser for organomercurial speciation in environmental samples

Performance of commercial Trace Mercury Analyser (TMA) originally devoted to total mercury content analyses in solid and liquid samples was tested in off-line combination with HPLC technique for speciation purposes. RPHPLC system optimized for baseline separation of mercury(II), methylmercury and phenylmercury rendered fractions with volumes directly acceptable by TMA. The main problems of this combination via off-line interfacing i.e. volatility of organomercurials and lost of fractions due to overflow from porous nickel and/or platinum transfer boats were solved by addition of wetting agent (cetyltrimethylammonium bromide) and stabilizing agent (dithizone) into the vessels prior to fractions collection. Calibration curves were measured for Hg(II) and methylmercury within range from 25 ppb to 500 ppb and were linear with correlation coefficients better than 0.9997. Detection limits achieved were around 0.3 ng for both mercury species. No matrix effects were observed during analyses of tap and surface water samples spiked at low ppb levels.     

Mercury speciation by coupling cold vapour atomic absorption spectrometry with flow injection on-line preconcentration and liquid chromatographic separation

A fully automated system for the direct determination of methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) at the ng/L level is described. It is based on solid phase extraction preconcentration incorporated in a flow injection (FI) system, high performance liquid chromatography (HPLC) separation, reduction combined with thermolysis and determination by cold vapour atomic absorption spectrometry (CVAAS). For preconcentration a microcolumn of bonded silica with octadecyl functional groups (C18 reversed phase material) was used as a sorbent for the mercury complexes formed on-line with ammonium pyrrolidine dithiocarbamate. Retained mercury species are eluted with a methanol-acetonitrile-water mixture and subjected to separation on an octadecylsilane (ODS) column before determination by CVAAS. The sensitivity of organo-mercury determination could be improved by using NaBH₄ as a reductant combined with a thermolysis step. In order to perform on-line measurements the preconcentration microcolumn was mounted in a pressure-tight casing. Limits of detection for MeHg, EtHg, PhHg and Hg(II) employing a sample volume of 58.5 mL were 9, 6, 10 and 5 ng/L, respectively. The relative standard deviation (RSD) calculated from 9 repeated measurements was found to be 3.6%, 5.5%, 10.4% and 7.6% for MeHg, EtHg, PhHg and Hg(II), respectively. Finally, the application of this method for speciation of mercury in fish and human urine is described.     

Spectrofluorometric method for determination of the total mercury content in environmental samples — Waste waters

A highly selective spectrofluorometric method for the determination of total mercury (Hg) in waste waters is described. Fluorescence quenching of rhodamine B with Hg(II) in the presence of iodide, after a concentration step, is the basis of this sensitive method. All forms of mercury, including organic compounds, are pre-oxidized to ionic mercury by acidic potassium permanganate. The final and complete oxidation is achieved by adding potassium persulphate and heating. 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. The recoveries were done by adding 3.0 g Hg/100 ml to each sample before the digestion. It was indicated that the recoveries for determining mercury in waste waters were 98.3%–102.7%. The method gives reliable results down to a concentration of 10 ng Hg/ml waste water.     

Speciation analysis for mercury in gas condensates by capillary gas chromatography with inductively coupled plasma mass spectrometric detection

A method allowing species-selective determination of atomic mercury, non-polar dialkylated mercury compounds,polar monoalkylated species and inorganic mercury complexes in natural gas condensates was developed. Inductively coupled plasma mass spectrometry was employed as a detection method for capillary gas chromatography and compared with microwave induced plasma atomic emission detection for the analysis of hydrocarbon-rich matrices. The method was based on two consecutive injections allowing comprehensive speciation analysis. First a sample aliquot was diluted with toluene and analysed for Hg0 and individual dialkylmercury compounds. Then, another aliquot was butylated with a Grignard reagent for the species specific determination of Hg(II) and monoalkylated mercury species. The detection limits were down to 0.08 pg level.     

Development of a multi-component chemically reactive detection conjugate for the determination of Hg(II) in water samples

Mercury ions (Hg(II)) are considered highly toxic and hazardous element even at low levels. The contamination of Hg(II) is a global problem. To develop selective and sensitive technique for the detection of Hg(II) has attracted considerable attention. In this study, a multi-component chemically reactive detection conjugate for determination of Hg(II) has been synthesized and a competitive format assay was proposed. In the technique, the chemically reactive capture conjugate was coated on the plate. The reactive detection conjugate was then captured by the capture conjugate. TMB solution was added and catalyzed by HRP molecules immobilized on AuNPs. Finally, the developed enzymatic signal was measured at 450 nm. The linear range of the assay was 0.35–350 ppb with a detection limit of 0.1 ppb. The average recoveries of Hg(II) from mineral water, tap water and lake water were 100.03%, 103.13% and 102.03%, respectively. All coefficients of variation (CVs) were less than 10%. The results are closely correlated with those from inductively coupled plasma mass spectrometry (ICP-MS), which indicated that the developed technique is a reliable method for and sensitive detection of Hg(II) in water samples.     

A plasmonic mercury sensor based on silver–gold alloy nanoparticles electrodeposited on indium tin oxide glass

We construct silver–gold alloy nanoparticles (Ag–AuNPs) as the basis of a reagentless, sensitive and simple mercury sensor. Ag–AuNPs were electrodeposited directly on transparent indium tin oxide film coated glass. Hg(II) ions in aqueous solution could be reduced by Ag atoms existing in Ag–AuNPs; the deposition/amalgamation of Hg on the nanoparticles resulted in a blue shift of the localized surface plasmon resonance peak. Therefore, Hg^2 + can be detected quantitatively by using a spectrophotometer. The sensor response is linear in the range from 0.05 to 500 ppb of Hg(II) concentration. No sample separation or preconcentration is required for detection of ultralow levels of mercury in water samples. The results shown herein have potential applications in the development of a new optical sensor for the detection of low concentrations of mercury.