Flow-through stripping chronopotentiometry for the monitoring of mercury in waste waters

A simple method for the determination of total mercury in waste waters is described. It makes use of a flow system incorporating a wall-jet cell equipped with a gold working electrode. The untreated sample is mixed on-line with the acidic carrier electrolyte which contains potassium permanganate and transforms the various species of mercury, especially elementary Hg, to Hg(II). The pre-treated solution enters the cell where mercury is deposited on the gold electrode. In the next step the deposit is stripped at constant current and the time corresponding to the dissolution of the deposit is obtained from the chronopotentiometric signal. The method enables it to determine and monitor Hg in the concentration range of 1 to 1000 μg/L in 5 min intervals. Received: 20 October 1997 / Revised: 23 December 1997 / Accepted: 30 December 1997     

Sensitive and selective determination of mercury by differential pulse stripping voltammetry after accumulation of mercury vapour on a gold plated graphite electrode

 A selective and sensitive method is proposed for the determination of mercury by anodic stripping voltammetry after its preconcentration from the gas phase. Mercury from the sample solution is reduced to elemental Hg by SnCl₂ and volatilized by the bubbles of a carrier gas. The gas containing mercury vapour is dried and passed through a capillary onto a gold coated graphite electrode. An anodic stripping voltammogram is recorded from 0.1 mol/l HClO₄+3×10^-3 mol/l HCl solution. The calibration curve is linear from 1×10^-9 to 4×10^-8 mol/l Hg(NO₃)₂. The absolute detection limit is 0.46 ng Hg. The relative standard deviations for 4×10^-9 mol/l and 2×10^-8 mol/l Hg(NO₃)₂ are 9.8% and 6.1%, respectively (n=5). Received: 18 December 1995/Revised: 16 April 1996/Accepted: 20 April 1996     

Anodic stripping voltammetric determination of Zn, Pb and Cu traces in whisky samples

The simultaneous “in natura” determination of trace Zn, Pb and Cu in whisky samples by anodic stripping voltammetry (ASV), using a hanging mercury drop electrode, without previous treatment or addition of supporting electrolyte is described. The choice of an appropriate stripping voltammetric method and deposition potential minimizes the influence of the organic content and ensures a good reproducibility of the measurements. The reliability of the method was tested comparing the results with those of atomic absorption spectroscopy (AAS), with differences of about 10%. The method allows the determination of heavy metal ions in the μg L^–1 range. Received: 14 August 1997 / Revised: 10 December 1997 / Accepted: 11 December 1997     

Automatic kinetic determination of Hg(II) by anodic stripping potentiometry with constant current oxidation

A new kinetic method for the determination of Hg(II) is proposed. It is based on the kinetic evolution of the anodic stripping potentiometric curves yielded by a gold electrode previously coated with mercury upon passage of constant electrical currents. The method features a linear determination range between 40 and 800 ppb of Hg(II) and a relative standard deviation of 5% (n = 9) for a mercury concentration of 200 ppb. The experiments were conducted on a customized automatic set-up, and instrumentation, data acquisition and processing were all governed by means of a QBASIC program (PSAKINEL) written by the authors.     

Determination of mercury traces by differential-pulse stripping voltammetry after sorption of mercury vapour on a gold-plated electrode

Trace mercury is reduced with tin(II) to mercury metal, which is volatilised by bubbling air through the solution. A certain fraction of this mercury is sorbed on a rotating gold disk electrode and stripped in a thiocyanate solution. The detection limit is about 30 ng Hg(II) in solution; the relative standard deviation is 6% for 100 ng Hg(II) (n = 7). The detection limit for mercury in air is 1.7 ng l^?1 with a preconcentration time of 10 min.     

Calibrationless determination of mercury by flow-through stripping coulometry

Trace concentrations of Hg were determined in a flow-system by constant current stripping chronopotentiometry in coulometric mode. Mercury was electrodeposited from the flowing sample solution in an electrochemical flow-through cell on a large surface porous electrode plated with a thin layer of gold. The deposited mercury was then stripped with constant current and the potential change of the working electrode was recorded and evaluated. Since complete electrochemical yields were achieved at both the deposition and dissolution steps, the mercury concentration in the sample solution could be calculated from Faradays law. The detection limit and reproducibility of the method were about 0.1 ng/ml for 10 ml sample solution and 4%, respectively. The time for a complete analysis was 2 to 5 min. The utility of the method was demonstrated with the analysis of reference materials, water samples, waste materials, plants and charcoal catalysts.     

Study of Bare and Mercury‐Coated Vibrated Carbon,Gold and Silver Microwire Electrodes for the Determination of Lead and Cadmium in Seawater by Anodic Stripping Voltammetry

Carbon, gold and silver microwires are revisited under vibrated conditions for detection of trace lead and cadmium in seawater. The Pb and Cd peaks fully overlapped on the bare gold and carbon electrodes and partially on the silver electrode. The sensitivity of all three was insufficient for detection in uncontaminated waters. Peak separation was obtained after coating with mercury (Hg). Only the Hg‐coated silver electrode is suitable when preplated. Limits of detection for Pb using the Hg/C and Hg/Ag electrodes (20–40 pM), and Cd (70 pM), are sufficiently low for Pb and Cd detection in seawater.     

水中痕量汞的半微分阳极溶出分析

本文提出了测定痕量汞的半微分阳极溶出伏安法。玻碳电极用2,2’-联吡啶乙醇溶液进行修饰后再电镀—层金膜。支持电解质为0.1mol/HCl,修饰电极的重现性和灵敏度优于未修饰电极。讨论了予电解电位、予电解时间、电极转速和支持电解质的影响。溶出峰高与汞浓度在0.2～60ng/ml范围内呈良好线性关系,检测下限为0.11ng/ml。本法已用于自来水、雨水和深井水中汞的测定,获得满意结果。     

Voltammetric study of the redox behaviour of the Hg(II)/Hg(I)/Hg system at a rotating metal-ring/glassy-carbon disc electrode

The reduction of Hg(II) at a glassy-carbon electrode in various electrolytes has been studied by rotating ring-disc voltammetry. Reduction proceeds directly to metallic mercury in a single 2-electron step. However, at the foot of the wave, and only during the first reduction sweep after pretreatment of the electrode surface, a small amount of Hg(I) species is detected at the ring. The appearance of an Hg(I) intermediate is most pronounced in sulphuric acid solution. The reduction of Hg(II) is found to proceed irreversibly and to be of first order. At sufficiently negative potentials the reduction is convective-diffusion controlled. Stripping voltammetric experiments indicate that the dissolution of mercury gives Hg(II) in complexing electrolytes. In non-complexing electrolytes the initially formed Hg(II) reacts with mercury atoms on the electrode surface to give Hg(I). During electrodissolution, two stripping peaks may be observed as a result of underpotential adsorption of mercury on glassy carbon. The difference in peak potential between the adsorption (mono) layer peak and the bulk mercury peak has been related to the difference in work functions of the deposit (mercury) and substrate (carbon). A rotating glassy-carbon electrode has been used for the anodic stripping determination of mercury. When an appropriate amount of a cation such as cadmium(II) or copper(II) is added to the test solution, mercury down to 2 x 10(-9)M (0.4 ng ml ) can be determined in acidified thiocyanate electrolyte with a relative standard deviation of about 22%.     

Modified solid electrodes for stripping voltammetric determination of tin

The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment. Received: 20 December 1996 / Revised: 11 March 1997 / Accepted: 13 March 1997     

Modified solid electrodes for stripping voltammetric determination of tin

The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment. Received: 20 December 1996 / Revised: 11 March 1997 / Accepted: 13 March 1997     

金纳米颗粒@碳微球的制备及其电化学检测汞离子性能研究

本文研究了金纳米颗粒@碳微球(Au@CMSs)的制备及水环境中汞离子在该材料上的电化学行为. 实验结果表明,在0.1mol•L^-1 pH = 5.0的NaAc-HAc缓冲溶液中,采用方波伏安法测定汞离子,其浓度与氧化峰电流强度线性良好,相关系数为0.997,检出限为3.69 × 10^-8 mol•L^-1（3σ方法）.     

Electrochemical studies of mercury(II)

The reduction of Hg²⁺ is studied by linear sweep voltammetry, rotated disk electrode voltammetry, and chronoamperometry in a non-complexing medium at a vitreous carbon electrode (VCE). At the VCE which is completely free of any mercury deposit, the reduction of Hg²⁺ is found to be of first order, involving two electrons and reversible at slow sweep rates. When the VCE is partially covered with mercury droplets, the reduction mechanism is different and occurs in two steps. At the most active sites on the VCE where mercury droplets are formed during a previous cathodic sweep, Hg²⁺ undergoes disproportionation to Hg₂²⁺ which is subsequently reduced to Hg. The second step involves the simple two-electron, diffusion-controlled reduction of Hg²⁺ to Hg at the bare electrode surface.     

Determination of Mercury with a Miniature Sensor for Point-of-care Testing

In developing countries, subsistence gold mining entails mixing metallic mercury with crushed sediments to extract gold. In this approach, the gold−mercury amalgam is heated to evaporate mercury and obtain gold. Thus, the highly volatile mercury can be absorbed through inhalation, resulting in adverse health effects. Urinalysis can be used to detect mercury, which is excreted in urine and feces, and correlate exposure with toxic effects. The current gold standard analytical methods are based on fluorescence or inductively coupled plasma mass spectrometry methods, but are expensive, time consuming, and are not easily accessible in countries where testing is needed. In this work, we report on a miniature electrochemical sensor that can rapidly detect mercury in urine at levels well below the US Biological Exposure Index (BEI) limit of 50 ppb (μg/L). The sensor is based on a thin-film gold electrode and anodic stripping voltammetry electroanalytical approach. The sensor successfully detected mercury at trace levels in urine, with a limit of detection of ∼15 ppb Hg in the linear range of 20–80 ppb. With the low-cost disposable sensors and portable instrumentation, it is well suited for point-of-care applications.     

Chelating resin preconcentration and Hg(II) assisted elution followed by differential-pulse anodic stripping voltammetry for the determination of Cd, Cu, and Pb in seawater

A new and efficient Hg(II) back-elution method for the desorption of Cd, Cu, and Pb from Chelex-100 chelating resin was developed. A smaller eluent volume and shorter elution time can be achieved using an Hg(II) containing eluent rather than pure nitric acid. Owing to the remaining Hg(II) ion in the effluent, a mercury thin-film electrode is formed in-situ during the anodic stripping voltammetric determination without any further addition of Hg(II). The results indicate that all the analytes in seawater matrix can be completely adsorbed on Chelex-100 resin from the sample at pH 6.5, and subsequently eluted from the resin with an acid solution of 5 × 10^–4 mol/L Hg²⁺ + 1 mol/L HClO₄. The detection limits obtained from the differential-pulse anodic (μg L^–1 to ng L^–1) stripping voltammetry are at sub-ppb to ppt (μg L^–1 to ng L^–1) levels permitting to determine Cd, Cu and Pb traces in seawater. The analytical reliability was confirmed by the analysis of the certified reference material CASS-II (open ocean seawater). Received: 22 April 1997 / Revised: 5 August 1997 / Accepted: 7 August 1997     

Mercury‐modified Lignosulfonate‐stabilized Gold Nanoparticles as an Alternative Material for Anodic Stripping Voltammetry of Thallium

Lignosulfonate‐stabilized gold nanoparticles (AuNPs‐LS) were synthesized and subsequently used as a complexing agent for mercury ions. The obtained AuNPs‐LS/Hg²⁺ complex was characterized by means of various physicochemical techniques such as UV‐vis spectroscopy, transmission electron microscopy and cyclic voltammetry. Furthermore, the resulting complex was evaluated as an electrode modifier for the development of amperometric sensors. Upon sufficient negative potential, the bound mercury ions are reduced to form an amalgam with AuNPs‐LS. Thus, the performance of glassy carbon electrode (GCE) modified by AuNPs‐LS/Hg film was investigated as an electrochemical sensor in the determination of Tl⁺ ions in a 0.05 M EDTA at pH 4.5. The presence of the mercury containing film improves the analyte accumulation due to its ability to form a fused amalgam with thallium. The presented data indicate that the GCE/AuNPs‐LS/Hg modified electrode shows better performance toward Tl⁺ determination in comparison to bare GCE. The stripping anodic peak current of thallium was linear over its concentration range from 1.7⋅10⁻⁷ to 5.0⋅10⁻⁶ M. The detection limit (3σ) was estimated to be 1.4⋅10⁻⁷ M. The proposed method was successfully applied for the determination of thallium ions in real samples of soil derived from the area of the copper smelter near Głogów (Poland).     

Measurements of trace concentrations of mercury in sea water by stripping chronopotentiometry with gold disk electrode: influence of copper

A stripping chronopotentiometric method, using a rotating gold disk electrode for mercury measurements in sea water is described. Compared with a same method using a stationary gold film electrode, this method has a eight times higher sensitivity and a detection limit of 5 ng l⁻¹ after 10 min deposition time. Moreover, the time needed for gold plating is eliminated. Compared with other electrochemical methods capable of measuring mercury at low concentrations, the present method is more simplified with no degassing step and no need to use a medium-exchange procedure before the stripping step. These characteristics render the method easily practicable on board oceanographic vessels for ‘in situ’ measurements.     

Differential-pulse anodic stripping voltammetry of mercury with gold-film micro-electrodes

Cylindrical gold film micro-electrodes are easily produced by plasma-sputtering of gold onto carbon fiber electrodes. The micro-electrodes produced were found to maintain their cylindrical geometry indefinitely, unlike gold wire electrodes of similar dimensions. Application of these electrodes in differential-pulse anodic stripping voltammetry provides a method for quantifying trace levels of mercury(II). Up to 100 μg l^?1 Hg(II) the area of the mercury stripping peak varied linearly with mercury concentration; the detection limit was 3.7 μg l^?1. With more than 100 μg l^?1 Hg(II) a new mercury stripping peak grows in at less positive potentials; its peak height is linear with Hg(II) concentration.     

Determination of mercury by differential-pulse anodic-stripping voltammetry with various working electrodes Application to the analysis of natural water sediments

Four types of working electrode (glassy-carbon and gold rotating-disk electrodes and two types of gold-film electrode) have been used in determination of traces of mercury by differential-pulse anodic-stripping voltammetry, and the analytical parameters of the procedures compared. The technique has been applied to the analysis of river sediments. The lowest limit of detection (0.02 μg/l.) was obtained with the gold rotating-disk electrode. Two procedures have been found optimal for analyses of sediment samples; determination with the gold rotating-disk electrode and solution-exchange after the preelectrolysis, and determination with the gold-film electrode prepared in situ in the sample extract. The sample pretreatment involved a separation of the 0.45–63 μm fraction, mineralization with a mixture of hydrochloric and nitric acids (3:1 or 1:3) under atmospheric pressure in a fused silica vessel, followed by irradiation with ultraviolet light, after addition of hydrogen peroxide (to destroy organic matter). The most serious interference is from iron; this can be prevented by adding fluoride or pyrophosphate. The procedure is an alternative to the AAS determination of the total mercury content in sediments, especially with heavily polluted samples (mercury concentrations up to 0.01%).     

Oligonucleotide Functionalized Microporous Gold Electrode for the Selective and Sensitive Determination of Mercury by Differential Pulse Adsorptive Stripping Voltammetry (DPAdSV)

Abstract

A novel electrode modified with oligonucleotide and microporous gold was fabricated for the determination of mercury by differential pulse adsorptive stripping voltammetry (DPAdSV). Microporous gold was synthesized by electrochemical reduction using dynamic hydrogen bubble template. The oligonucleotide was immobilized on microporous gold by self-assembly. The prepared electrode exhibited an improved electrochemical response for mercury(II) ion because of the large surface area and excellent electron transfer capacity provided by microporous gold and the specific coordination between mercury ion and thymine bases in oligonucleotides. Under the optimal experiment conditions, the oligonucleotide functionalized microporous gold electrode had a linear relationship between the stripping current and mercury ion concentration in the range from 0.5 to 30?µg/L with a detection limit of 0.021?µg/L. Moreover, the prepared electrode exhibited good selectivity, reproducibility, repeatability and stability. Furthermore, the prepared electrode was applied to detect mercury in tap water with satisfactory results.