脉冲溶出伏安法中汞膜碳纤维电极性能的研究

采用脉冲阳极溶出伏安法,研究了汞膜碳纤维电极测定痕量金属离子的行为,并与汞膜玻碳电极和悬汞电极进行了系统的对比,显示了碳纤维电极在静止态溶液、极稀溶液、有机溶液和双电极体系中具有特殊的优越性。本文对该电极的制作,预处理和实际测试条件进行了探讨。     

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     

电化学活化玻碳/铋膜电极制备及铅、镉离子敏感分析法

以电化学活化玻碳为基底电极原位制备金属铋膜电极,用之于分析Pb2+、Cd2+.方法如下:在氢氧化钠溶液中,由恒电位或循环扫描电位方法活化玻碳电极,随后以稀盐酸替代传统的醋酸缓冲液作为分析溶液将Bi3+与Pb2+、Cd2+共沉积在活化玻碳电极表面,再以方波阳极溶出分析法(SWASV)检测金属离子.结果表明:经简单的电化学清洗步骤即可高重现地再生电极表面,大幅度提高检测Pb2+、Cd2+的灵敏度,检测范围也可拓展至高卤素离子含量的样品.     

Determination of lead and cadmium in seawater using a vibrating silver amalgam microwire electrode

Silver amalgamated electrodes are a good substrate to determine lead (Pb) and cadmium (Cd) in seawater because they have properties similar to mercury but without the free mercury (Hg). Here a silver amalgamated microwire (SAM) electrode is optimised for the determination of Pb and Cd in coastal waters and uncontaminated ocean waters. The SAM was vibrated during the deposition step to increase the sensitivity, and electroanalytical parameters were optimised. The Hg coating required plating from a relatively concentrated (millimolar) solution, much greater (500×) than used for instance to coat glassy carbon electrodes. However, the coating on the ex situ amalgamated electrode was found to be stable and could be used for up to a week to determine trace levels of Pb in seawater of natural pH. The limit of detection square-wave ASV (50 Hz) using the pre-plated SAM electrode was 8 pM Pb using a 1-min plating time at pH 4.5. The limit of detection in pH 2 seawater was 4 pM using a 5-min plating time, and it was 12 pM using a 10-min plating time at natural pH in the presence of air, using a square-wave frequency of 700 Hz. The vibrating SAM electrode was tested on the determination of Pb in reference seawater samples from the open Atlantic (at the 20 pM level), Pacific, and used for a study of Pb in samples collected over 24 h in Liverpool Bay (Irish Sea).     

Sonoelectroanalytical detection of lead at a bare copper electrode

The sonochemically facilitated, mercury free detection of Pb2+ at a copper electrode has been investigated as a means of simplifying the quantification of this important analyte and to minimise the interference of copper ion. The procedure relies upon maximising the formation of Pb-Cu intermetallic compounds leading to the emergence of a single, easily quantifiable stripping signal. Linear responses to Pb2+ were obtained with a sensitivity comparable to that obtained at a bare glassy carbon electrode. Interference from Cu2+, Zn2+ and Cd2+ was assessed on the copper electrode with no appreciable change in the Pb2+ voltammetric profile observed. In contrast, bare glassy carbon showed a significant change in Pb2+ voltammetric profile as Cu2+ was added, due to the formation of intermetallic species.     

微波消解-溶出伏安法对食品中铜、铅、镉的同时测定

采用微波消解结合同位镀汞阳极溶出伏安法对茶叶、紫菜和西洋菜等食品中的铜、铅、镉进行了测定,并优化了微波消解、电解缓冲液、富集电位等实验条件。采用标准加入法定量,Cu、Pb、Cd的线性范围分别为0.040~1.768、0.080~1.768、0.040~1.768 mg/L,相关系数分别为0.998 4、0.998 2、0.997 0,检出限分别为0.008、0.016、0.008 mg/L,相对标准偏差(n=5)分别为4.1%、0.92%、2.0%。该方法测定茶叶、紫菜、西洋菜等实际样品的铜、铅、镉含量,加标回收率分别为98%~109%、94%~103%、100%~112%;将测定结果与原子吸收光谱法检测结果对比,表明此方法简便、快速,且具有较高的灵敏度、较好的选择性和可靠性。     

Determination of Mercury by Chronopotentiometric Stripping Analysis Using Glassy Carbon Vessel as a Working Electrode

In this work chronopotentiometric stripping analysis of mercury was performed using a process vessel of glassy carbon as a working electrode. Experimental parameters for both steady and rotating vessel were investigated and compared. Relative sensitivity as well as the sharpness of the analytical signal was better when the rotation of the process vessel was performed. The new design provided better sensitivity when compared to both stationary and rotating glassy carbon disk electrodes. Detection limit obtained for the electrolysis time of 600 s was 0.1 ng/L of Hg(II). The accuracy of the technique was confirmed by analyzing the standard reference material – tomato leaves.     

Ion-exchange voltammetry with nafion/poly(sodium 4-styrenesulfonate) mixed coatings on mercury film electrodes: characterization studies and application to the determination of trace metals

This work aimed to produce improved polymer coatings for the modification of thin mercury film electrodes (TMFEs). The goal is to obtain sensitive, reproducible, mechanically stable and antifouling devices suitable for the determination of trace metal cations in complex media. Therefore, novel mixed coatings of two sulfonated cation-exchange polymers of dissimilar characteristics-Nafion (NA) and poly(sodium 4-styrenesulfonate) (PSS)-were produced by solvent evaporation onto glassy carbon electrodes. The effect of the mass ratio (NA:PSS) on the film morphology was studied by scanning electron microscopy, revealing the formation of biphasic polymer systems, where PSS bead-shaped clusters appeared randomly dispersed into a uniform and compact NA environment. The permselectivity/ion-exchange features of the mixed films onto glassy carbon were evaluated using cathecol, urate, and dopamine. To allow trace metal analysis, thin mercury films were plated through the NA/PSS coatings, being the reproducibility and ion-exchange features of the mixed coatings-TMFE evaluated using lead ions. The best NA/PSS coating was found for the mass ratio of 5.3. Analytical performance of the NA/PSS-TMFE yielded a detection limit of 5.5 nM (3sigma), and the application of this modified electrode to an untreated polluted estuarine water sample produced significant improvements in the quality of the signal compared with that for a bare TMFE.     

Redox magnetohydrodynamic enhancement of stripping voltammetry: toward portable analysis using disposable electrodes, permanent magnets, and small volumes

The use of redox magnetohydrodynamics (MHD) to enhance the anodic stripping voltammetry (ASV) response of heavy metals has been investigated, with respect to achieving portability: disposable electrodes consisting of screen-printed carbon (SPC) on a low temperature co-fired ceramic (LTCC) substrate, small volumes, and permanent magnets. The analytes tested (Cd(2+), Cu(2+), and Pb(2+)) were codeposited on SPC with Hg(2+) to form a Hg thin film electrode. High concentrations of Fe(3+) were used to produce a high cathodic current which generates a significant Lorentz force in the presence of a magnetic field. This Lorentz force induces solution convection during the deposition step, enhancing the mass transport of analytes to the electrode and increasing their preconcentrated quantity in the mercury thin film. Therefore, larger ASV peaks and improved sensitivities are obtained, compared to analyses performed without a magnet. The effects on ASV signal of varying Hg(2+) concentration (0.10 and 1.0 mM), deposition time (10-600 s), and electrode surface roughness were investigated. In addition, analyses were performed using a real lake water matrix. By using the disposable LTCC-SPC working electrodes in small volumes (150 microL) and with small permanent magnets (0.78 T), peak areas were increased by 75% when compared to the signal obtained in the absence of a magnetic field. A limit of detection of 25 nM for Cd(2+) was observed with only a 1 min preconcentration time.     

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.     

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.     

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.     

Electroanalytical detection of zinc in whole blood

Three different electroanalytical techniques for the determination of zinc in blood are investigated. The direct determination in diluted blood via anodic stripping voltammetry at glassy carbon and the use of Nafion-coated glassy carbon mercury electrodes are shown to lack the necessary sensitivity whereas an acoustically assisted double extraction followed by sono-ASV using a glassy carbon electrode is found to be rapid, reliable and sensitive.     

Influence of hydrodynamic conditions of the solution on the sensitivity of stripping analysis of trace metals

Possibilities to increase the sensitivity of stripping analysis by optimising the hydrodynamic conditions of the solution during the deposition and rest period are evaluated. Rotation rates as high as 13 000 rpm can be applied during the deposition step at a mercury film rotating disc electrode for Zn, Cd, Pb, In and Tl determinations when 10-20 mg/l of Hg(2+) for the renewal of the mercury film is added. Because of the extreme sensitivity on the properties of the mercury film in the case of Ga only 4000-5000 rpm are recommended. The highest stirring efficiencies using a magnetic stirrer are equivalent to 2500-3000 rpm when a rotating disc electrode is used. The effect of the duration of the rest period is not significant for square wave stripping voltammetry, however, analytical signals can be increased 10 and more times when potentiometric stripping analysis is applied.     

Application of Square Wave Anodic Stripping Voltammetry for Determination of Traces of Ti(I) at Carbon Electrodes In Situ Modified with Bi Films

Bismuth films deposited in situ at glassy carbon and carbon film electrodes were tested for the determination of traces of Tl(I) separately and together with Zn(II) and Pb (II), in acetate buffer solution pH 3.7, using square wave anodic stripping voltammetry. Electrochemical impedance spectra in the presence of Tl(I) showed differences between the electrode substrates. The sensitivity to Tl does not depend on the presence of other ions, and was better at carbon film electrodes, although the 2 nmol L^?1 detection limit was independent of electrode substrate. Application to the measurement of Tl(I) in commercial berry juice is demonstrated.     

Nafion Film Immobilized Nano Ag‐Hg Amalgam Glassy Carbon Electrode Used for Simultaneous Determination of Lead,Cadmium and Copper

In this work, a new route to reduce the toxicity of the mercury electrode was presented. Nafion was used as soft template to generate nanosized Ag‐Hg amalgams on the surface of a glassy carbon electrode other than the traditional preparation of solid amalgam electrodes. As less mercury was used and it was immobilized by Ag and Nafion film, the toxicity of mercury was reduced. Scanning electron microscope (SEM) showed that the size of the formed nano Ag‐Hg amalgams was about 50 nm. Finally, the prepared electrode was used to the determination of heavy metals. Good reproducibility, linearity and sensitivity were obtained when it was utilized for the determination of Cd²⁺, Pb²⁺ and Cu²⁺ in deionized water and in tap water (without any further treatment).     

A study on the electroanalytical performance of a bismuth film-coated and Nafion-coated glassy carbon electrode in alkaline solutions

Bismuth film electrodes are widely used for determination of heavy metal ions in acidic solutions, while alkaline solutions are rarely employed. We have compared the deposition of Bi(III) and Pb(II) on a Nafion-coated glassy carbon electrode in alkaline and acidic solutions. The results indicate that both Bi(III) and Pb(II) can be deposited in either alkaline or acidic solution, but the quantity of Pb(II) deposited in alkaline solution is less than that in acidic solution. The modified electrode was used to determine heavy metal ions in both alkaline and acidic solutions, and the results of the method agree well with those of atomic absorption spectroscopy.     

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.     

Stripping voltammetry in environmental and food analysis

The review covers over 230 papers published mostly in the last 5 years. The goal of the review is to attract the attention of researchers and users to stripping voltammetry in particular, its application in environmental monitoring and analysis of foodstuffs. The sensors employed are impregnated graphite, carbon paste, thick film carbon/graphite and thin film metallic electrodes modified in-situ or beforehand. Hanging mercury drop electrodes and mercury coated glassy carbon electrodes are also mentioned. Strip and long-lived sensors for portable instruments and flow through systems are discussed as devices for future development and application of stripping voltammetry.     

Electrodeposition of mercury film on electrodes modified with clay minerals

A new type of carbon paste electrode modified with clay mineral and covered with a mercury film is presented in this work. Electrodeposition of the mercury film was performed on the carbon paste electrode modified with montmorillonite. The mercury film was deposited by both electrodeposition in situ and a preliminary electrodeposition. The pre-deposited film of mercury showed to be suitable for anodic stripping voltammetry. An open-circuit sorption of Cd, Pb, and Cu with subsequent anodic stripping voltammetry exhibited higher current responses of metals. Besides the enhanced sensitivity superior separation of the current responses during a simultaneous stripping of metals is expected to be achieved by means of the newly prepared electrode. Presented at the 57th Congress of Chemical Societies, Tatranské Matliare, 4–8 September 2005.