Renewable silver amalgam film electrodes in electrochemical stripping analysis—a review

The success of a voltammetric sensing procedure depends mainly on the proper choice of the working electrode. This is because its ability to accumulate the analyte determines the sensitivity of the method. The main criterion of the selection of the proper working electrode is the available potential window. A variety of conductive materials have been used for the preparation of working electrodes. Of these, two kinds of mercury electrodes—hanging mercury drop and film—were used because of their excellent voltammetric performance and, in particular, their high overpotential of hydrogen reduction. The significant drawbacks of mercury electrodes, however, are the toxicity of the material and the instability of liquid mercury films. To overcome these disadvantages, less toxic mercury-containing materials have been used, such as amalgams and amalgam film electrodes. This group includes renewable silver amalgam film electrodes used for electrochemical stripping sensing purposes. These electrodes have successfully been applied for anodic, adsorptive, cathodic, catalytic voltammetric, and potentiometric stripping determination of trace amounts of inorganic cations and organic compounds in various natural matrices. In this review, the electrode design, characteristics, and application of two kinds of renewable silver amalgam film electrodes are discussed in detail.     

Voltammetry of osmium-modified DNA at a mercury film electrode: application in detecting DNA hybridization

Mercury film electrodes (MFE) have recently been used in nucleic acid electrochemical analysis as alternatives to the classical mercury drop ones. DNA modified with osmium tetroxide, 2,2'-bipyridine (Os,bipy) can be detected with a high sensitivity at mercury electrodes via measurements of a catalytic osmium signal. In this paper we show that mercury film on a glassy carbon electrode can be used in voltammetric analysis of Os,bipy-modified DNA. Application of the MFE as a detection electrode in double-surface electrochemical DNA hybridization assay involving osmium labeling of target DNA is demonstrated.     

Nafion-coated mercury thin film electrodes for batch-injection analysis with anodic stripping voltammetry

Batch-injection analysis exhibits the advantages of rapid and simple electroanalysis of microlitre samples. Nafion-coated mercury thin film electrodes have been evaluated for use in batch-injection analysis with anodic stripping voltammetry (BIA-ASV). The advantages of Nafion-coated electrodes in reducing electrode contamination by components of complex matrices are combined with the analysis of small microlitre sample volumes. The measurement of traces of lead and cadmium is used to illustrate the approach. An optimised procedure for formation of Nafion-coated mercury thin film electrodes is evolved. The relative sensitivity for BIA-ASV at electrodes with and without Nafion coatings is 0.9 and 0.8 for cadmium and lead respectively; detection limits are 2 x 10(-9) M and 4 x 10(-9) M. Studies were done concerning the influence of surfactants and their effect was found to be much less with the Nafion film coating. Applications to real environmental samples are demonstrated.     

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper,lead and cadmium in sea water

The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.     

碳纤维微电极恒电位活化及测定金属离子的研究

碳纤维微电极已被广泛应用于电化学研究和分析测定,该电极尺寸极小,在分析性能上与常规电极有显著不同,在不镀汞的情况下,用碳纤维电极直接测定金属离子几乎没有明显的伏安响应,本文提出用+2.5 V恒电位预先活化碳纤维电极,使测定灵敏度大为提高,在双电极体系和静止溶液中,采用溶出伏安法可测定10~(-9)级金属离子,以同样的方法清洗电极,测定结果重现性良好,由于分析过程中不使用汞,该电极的测定范围大大增加,特别是用于氧化还原电位较正的金属离子测试,根据循环伏安法、扫描电镜和电子能谱的研究,发现碳纤维表面状况在处理前后有很大变化,并与测定灵敏度密切相关。     

Mercury film electrodes: developments,trends and potentialities for electroanalysis

In this article, the field of mercury film electrodes (MFE's) as electroanalytical devices is reviewed. Special emphasis is placed on the area of new materials as substrates for the mercury coating and the mercury plating process as well as on the developments related to the electrode modification used to achieve an increase in either the selectivity and/or the sensitivity of the analysis. Other topics discussed are microelectrodes, disposable electrodes and some novel, innovative or less well explored applications of electroanalytical methods using MFE's. The future prospects, potential uses and alternatives for MFE's in electroanalysis are finally discussed.     

A stannum-bismuth composite film electrode for simultaneous determination of zinc(II) and cadmium(II) using differential pulse anodic stripping voltammetry

The development and use of 'green' electrode materials is extremely attractive for the routine use of disposable metal sensors. Bismuth is an environmentally-friendly element and a bismuth film electrode was proposed as an alternative to mercury film electrodes. Compared with bismuth, stannum is a more 'environmentally friendly' material. The stannum-bismuth composite film electrode prepared by the in situ electrodeposition of stannum and bismuth on the glassy carbon substrate is reported for the first time. Compared with bismuth film and stannum film electrodes, the stannum-bismuth composite film electrode revealed better electroanalytical performance, and can be used as a possible alternative electrode for electrochemical stripping analysis of trace heavy metals.     

Poly(ester sulphonic acid) coated mercury thin film electrodes: characterization and application in batch injection analysis stripping voltammetry of heavy metal ions

Mercury-thin film electrodes coated with a thin film of poly(ester sulphonic acid) (PESA) have been investigated for application in the analysis of trace heavy metals by square wave anodic stripping voltammetry using the batch injection analysis (BIA) technique. Different polymer dispersion concentrations in water/acetone mixed solvent are investigated and are characterised by electrochemical impedance measurements on glassy carbon and on mercury film electrodes. The influence of electrolyte anion, acetate or nitrate, on polymer film properties is demonstrated, acetate buffer being shown to be preferable for stripping voltammetry applications. Although stripping currents are between 30 and 70% less at the coated than at bare mercury thin film electrodes, the influence of model surfactants on stripping response is shown to be very small. The effect of the composition of the modifier film dispersion on calibration plots is shown; however, detection limits of around 5 nM are found for all modified electrodes tested. This coated electrode is an alternative to Nafion-coated mercury thin film electrodes for the analysis of trace metals in complex matrices, particularly useful when there is a high concentration of non-ionic detergents.     

Nafion-coated bismuth film and nafion-coated mercury film electrodes for anodic stripping voltammetry combined on-line with ICP-mass spectrometry

Nafion-coated bismuth film electrodes (NCBFEs) and Nafion-coated mercury film electrodes (NCMFEs) were used to electrochemically preconcentrate metal analytes for subsequent analysis by inductively coupled plasma-mass spectrometry (ICP-MS). Either type of electrodes is part of a thin-layer electrochemical flow cell that is positioned upstream of a microconcentric nebulizer for the ICP-MS. Performances of these electrodes were compared in terms of the analytical "figures of merit" (e.g., dynamic ranges, reproducibility, hydrodynamic stability, and elimination of matrix effects detrimental to ICP-MS). The coupled technique (ASV-ICP-MS) is found to possess a wide dynamic range (at least 4 to 5 orders of magnitude) and to be reproducible. Both electrodes are much more stable than the thin mercury film electrode (TMFE) traditionally used for ASV-ICP-MS, with the lifetime of the NCBFE exceeding 8 h. Adopting these electrodes for ASV-ICP-MS overcomes the problems associated with a TMFE, the erosion of which decreases the sample throughput, affects the analysis precision, and contaminates conventional glass nebulizers and spray chambers of the spectrometer. The medium exchange procedure inherent in ASV is successfully implemented with a two-valve flow injection system for the accumulation of trace Cd2+ into the electrode from a certified seawater sample, followed by stripping Cd into a solution that is compatible to the ICP-MS operation.     

Determination of lead in blood by hydrodynamic voltammetry in a flow injection system with wall-jet detector

Lead is one of the most widely distributed toxic heavy metals in the environment. It is a cumulative poison, affecting the brain and nervous system. The threshold between the normal lead level and the level where physiological effects become manifest is relatively narrow. It is therefore desirable to screen exposed populations in order to identify the danger in time. The lead concentration in the blood is a measure to the total amount of lead in the body. A fast, accurate and cheap method for the determination of lead in blood is therefore needed. The conventional method used to determine lead in blood is atomic absorption. Electrochemical methods like stripping voltammetry combine high analytical sensitivity with relatively low cost for the equipment; however, electrode preparation is critical for the success of an analysis, and highly skilled personnel are needed. We describe an automated electrochemical method, using flow injection analysis with a wall-jet detector. Lead is released from its binding site in the blood by ion exchange and quantified by stripping voltammetry with a mercury film electrode (MFE). The method allows for the detection of 0.05 ppm Pb(2+) with an accuracy of about 10%. Electrode poisoning by proteins from the blood can be effectively suppressed when a MFE modified with a Nafion(R)-membrane coating is used. Such modified electrodes can be activated in the solution without further treatment, and used for more than 100 analyses before they have to be replaced. A solid matrix MFE with a Nafion(R)-membrane and all necessary chemicals for mercury film formation and lead release has been developed. Such electrodes are discussed as disposable electrodes for a portable blood lead detector.     

Square-wave anodic stripping voltammetry with a mercury-plated reticulated vitreous carbon electrode

A rotating mercury-plated reticulated vitreous carbon (RVC) electrode is tested for square-wave anodic stripping voltammetry; RVC provides very large surface areas which are easily plated with mercury. Despite the ill-defined geometry of the electrode, the square-wave stripping peaks are very well defined; their behaviour conforms partly to known theory for square-wave stripping from mercury film electrodes. Fast analytical determinations of lead and cadmium in the μg l^?1 range are facilitated by the high efficiency of the preconcentration step and the high sensitivity given by the stripping waveform.     

Brdicka-type processes of cysteine and cysteine-containing peptides on silver amalgam electrodes

Silver solid amalgam electrode (AgSAE) was used for differential pulse voltammetric (DPV) measurements of cysteine and cysteine-containing peptides, glutathione, gamma-Glu-Cys-Gly and phytochelatin (gamma-Glu-Cys)(3)-Gly (PC3), in the presence of Co(II) ions. It had been established earlier that cysteine-containing peptides and proteins catalyze hydrogen evolution at mercury electrodes in presence of cobalt salts; these processes are known as the Brdicka reaction. DPV signals measured with the AgSAE, the surfaces of which had been modified by mercury meniscus or mercury film, were qualitatively the same as those obtained with the hanging mercury drop electrode (HMDE). With these electrodes the number and the intensity of Brdicka signals of cysteine, glutathione and PC3 differed, making a distinction among them possible. On the other hand, with the polished silver solid amalgam electrode (the surface of which was completely free of liquid mercury) all three compounds produced only one but strikingly intense peak in the region of Brdicka reaction. Using this signal, cysteine, glutathione as well as PC3 could be determined at 10(-8)M level, representing sensitivity up to 2 orders of magnitude better than attained with the mercury-modified AgSAEs or HMDE.     

Flow potentiometric and constant-current stripping analysis for mercury(II) with gold,platinum and carbon fibre working electrodes : Application to the Analysis of Tap Water

Gold, platinum and carbon fibres with 10-μm diameter were mounted in PVC tubes and used as flow sensors in computerized potentiometric and constant-current stripping analysis for mercury, after electroplating ofa gold film onto the fibre surfaces. Compared to gold and glassy carbon disc electrodes, the fibre electrodes gare increased sensitivity and stability and were considerably simpler to handle. The gold-coated carbon fibre electrode gave a higher background than the gold fibre electrode, in both the potentiometric and constant-current stripping modes. Mercury(II) could be determined in presence of a 10⁵-fold (molar) amount of copper(II) by constant-current stripping in media with chloride concentrations below 0.05 M. The detection limit for mercury(II) after 10 min of electrolysis was 45 ng l^?1 at the 3 σ level.     

Voltammetry at the mercury film electrodes: Comparison of theoretical and experimental results obtained for indium in thiocyanate medium

The voltammetric behaviour of the In(III)-In(Hg) system was studied at the silver-, graphite-, and glassy carbon-based mercury film electrodes under cyclic and stripping conditions in thiocyanate media. The reversible curves obtained at high thiocyanate ion concentration showed a good agreement with theoretical predictions, particularly for the cathodic process. The anodic curves obtained at thin silver-based mercury film electrodes deviated from theoretical predictions due to the interactions between indium, dissolved in mercury, and the silver substrate of the film electrode. At low thiocyanate ion concentrations, where the current was controlled partly by the rate of the preceding chemical step and partly by diffusion, the variations in the film thickness affected the position of the curve as predicted theoretically for the reversible diffusion controlled case.     

Glucose Monitoring by a Biosensor Based on Mercury Thin Film Electrodes

Abstract

Mercury film electrodes consist of a thin film of mercury deposited on an electrode surface (typically glassy carbon) by reduction of a mercury (II) salt in solution. The surface area/volume ratio is larger for the mercury film electrode, and this electrode is more stable than mercury drop electrode, which allows a faster stirring rate to be used in the deposition step. An enzyme electrode is described, based on glucose oxidase immobilized by gelatin and glutaraldehyde and held over a glassy carbon electrode coated with a thin mercury film. This biosensor responds fast and linearly to glucose in a wide concentration range, which is significant because monitoring of glucose levels is a critical component of diabetes care. Certain optimization and characterization studies were carried out. Average value, standard deviation (SD), and variation coefficient (CV) were calculated with the help of the repeatability studies. Finally, glucose content of human blood samples was monitored with the help of the biosensor presented.     

Polymer-Mercury Coated Screen-Printed Sensors for Electrochemical Stripping Analysis of Heavy Metals

In the perspective of in-field stripping analysis of heavy metals, the use and disposal of toxic mercury solutions (necessary to plate a mercury film on a carbon electrode surface) presents a problem. The aim of this work was the development of mercury coated screen-printed electrodes previously prepared in the lab and ready to use in-field. Thus some commercially available polymers like Nafion®, Eastman Kodak AQ29®, and Methocel® were investigated as mercury entrapping systems for electrochemical stripping analysis of heavy metals. Screen-printed disposable cells with a silver pseudo-reference electrode, a graphite counter electrode, and a graphite working electrode were used. To modify the sensor, the polymer solution was cast onto the carbon working electrode surface. Detection limits of 0.8 and 1 μg/L were obtained for lead and cadmium respectively. Since Methocel® based electrodes showed the best performance, they were used for the analysis of real samples. The results were compared with those obtained using a classical thin mercury film electrode and ICP spectroscopy.

All the experiments reported here were performed in un-deareated solutions as required for in-field analysis.     

General characteristics of the copper-based mercury film electrode

The optimum conditions for the preparation, storage, conditioning and renewal of copper-based mercury film electrodes (CBMFEs) are given. The voltammetric results obtained at these electrodes are compared with the predictions of the theory of cyclic and stripping voltammetry at the mercury film electrode, as well as with the results obtained at the silver-based and the platinum-based mercury film electrodes. The advantage of a CBMFE is prolonged life-time, whereas the disadvantages ar the decreased range of usable positive potentials and the possibility of interfering reactions of the electrodeposited metals with the copper substrate or copper dissolved in the mercury phase. The presence of copper has no essential influence on the behaviour of lead and thallium; it affects the behaviour of zinc markedly and that of cadmium and indium slightly. The conditions allowing the minimization of the harmful action of copper on the behaviour of cadmium and indium have been found.     

Effect of the modification of mercuric oxide on the properties of mercury films at HgO-modified carbon paste electrodes

The influence of modifications of the mercuric oxide on the voltammetric properties of mercury film carbon paste electrodes was studied. The mercury film was formed electrochemically from the bulk red or yellow mercuric oxide-modified carbon paste electrodes. Differential pulse anodic stripping voltammetry and optical microscopy in polarised light were used to characterise the properties of the mercury films. The results were compared with those obtained using the conventional preparation of mercury-plated carbon paste electrodes when the mercury film is deposited on the surface of the electrode by reduction of Hg(II) ions in solution utilising a sufficient negative potential. It was shown that the mercury film formed from the yellow modification of the mercuric oxide provides better voltammetric characteristics than the red one owing to the high distribution of its small particles, i.e. the mercury droplets after electrochemical treatment. Such a mercury film has similar properties to those of a mercury film generated from solution. Received: 06 December 1999 / Accepted: 16 March 2000     

The determination of copper,lead and cadmium in sea water by differential pulse anodic stripping voltammetry

The effect of various instrumental parameters is investigated and optimized conditions established. The results are in accordance with the theory of differential pulse anodic stripping voltammetry. Both a hanging mercury drop electrode, and a rotating glassy carbon electrode mercury plated in situ were used. The best detection limit is obtained with the mercury film electrode, but the hanging mercury drop electrode is more reproducible. The differential pulse stripping technique is compared to linear sweep stripping, and increased sensitivity and better peak separation is demonstrated for the former technique, particularly when a hanging mercury drop electrode is used. However, the differential pulse technique will also improve the detection limit for a mercury film electrode, if the electrode has a non-ideal response with a corresponding high background current.     

Silver based mercury film electrode: Part IV. Comparison of theoretical and experimental voltammetric results obtained for cadmium

Using the silver based mercury film electrode (SBMFE) and cyclic and stripping voltammetric techniques the behaviour of cadmium has been compared with the behaviour of lead as well as with the predictions of the theory of de Vries and van Dalen. At the SBMFE with film thickness between 0.1 and 2 μm lead behaves with good agreement with theoretical predictions and only at thicknesses higher than 2 μm some deviations occur due to collecting of the excess mercury at the bottom of the wire electrode. On the other hand even at thin film electrodes the behaviour of cadmium deviates significantly from the predictions of the theory. The height of the anodic peak decreases and its width increases; also the displacement of the potentials of both cathodic and anodic peaks is smaller than the values predicted theoretically. The deviations are caused neither by the formation of intermetallic compounds in the bulk of mercury phase nor by the formation of heterogenous cadmium amalgam; they reflect the interaction between cadmium dissolved in mercury and the solid silver amalgam which is the substrate of the mercury film. Owing to the effect discussed the stripping determination of cadmium at SBMFE is characterized by a lower sensitivity and reproducibility.