Reference Electrodes Based on Solid Amalgams

A reference saturated calomel electrode based on the non‐toxic silver solid amalgam (SCE‐AgSA) as a substitute for liquid mercury is described. Long‐term as well as short‐term tests made during a period of one year confirmed the SCE‐AgSA potential to be equal to that of SCE within the limits of ±1 mV (the difference ΔE_SCE‐AgSA=+1.08±0.24 mV (vs. SCE); SD=0.87; N=51). The voltammograms of four selected metal ions registered vs. SCE‐AgSA and vs. SCE could practically overlap each other. None of the mentioned electrodes were polarized to a significant degree even if the electric current applied reached 2 mA. On the basis of the obtained results the SCE‐AgSA could be considered as equivalent substitute for SCE. Owing to practically identical electrode potential of both types of the mentioned electrodes the results obtained using SCE‐AgSA are completely comparable to those measured vs. SCE, without any correction of peak potentials.     

Working Electrodes from Amalgam Paste for Electrochemical Measurements

Paste electrode with paste amalgam as an active electrode material is described here for the first time. Designed electrode from silver paste amalgam (AgA‐PE) is solely metallic and does not contain any organic binder. Mechanical surface regeneration of AgA‐PE is performed in the same way as for classical carbon paste electrodes and reproducibility of such regeneration is about 10%. Electrochemical surface regeneration appeared very efficient for most measurements. In dependence on paste metal content, the electrode surface can be liquid (resembling a film) or rather solid. The hydrogen overvoltage on AgA‐PE is high, and the electrode allows measurements at highly negative potentials. AgA‐PE is well suited for study of reduction or oxidation processes without an accumulation step. Anodic stripping voltammetry of some metals tested on the electrode is influenced by formation of intermetallic compounds. The measurement based on cathodic stripping voltammetry (adenine, cysteine) and on catalytic processes from adsorbed state (complex of osmium tetroxide with 2,2′‐bipyridine) can be performed on AgA‐PE practically under the same conditions as found earlier for HMDE and for silver solid amalgam electrode. The working electrode from paste amalgam combines the advantages of paste and metal electrodes.     

Copper Solid Amalgam Electrodes

This work describes the behavior of copper solid amalgam electrodes (CuSAE). The applied potential range has been compared with that of the silver solid amalgam electrode (AgSAE) and the hanging mercury drop electrode (HMDE). In 0.05 M tetraborate buffer the applicable potential range of CuSAE is+0.945 V to ?1.75 V excluding ?0.2 V to ?0.5 V, where the anodic oxidation of copper occurs. CuSAE does not need other than electrochemical pre‐treatment, which has been documented by the evaluated repeatability of eleven voltammetric curves of Cd²⁺ (0.1 ppm), Pb²⁺ (0.1 ppm) and Mn²⁺ (0.5 ppm). The obtained results showed that CuSAE could substitute the solid copper, amalgamed copper or liquid copper amalgam electrodes, and can be applied for the study of systems needing an addition of Cu²⁺ ions into the measured solution.     

Carbon Powder Based Films on Traditional Solid Electrodes as an Alternative to Disposable Electrodes

The covering of conventional solid electrode with a film using an ink containing a conductive powder and a polymer enables to broaden the potential window of the original solid electrode. A solid silver amalgam electrode covered with such a film exhibits a potential window from ?600 mV to +1400 mV vs. SCE reference electrode. The renewal of the film is fast and simple: the electrode can be simply wiped with a filter paper to remove the old film and immersed into an ink solution or 1–2 μL of this ink solution can be applied to the surface of the electrode with a micro dispenser to form a new film. Therefore, just the inexpensive film at the electrode surface is disposable and there is no need to dispose the whole, more expensive electrode. Moreover, when a suitable electrochemical pretreatment of the film electrode is applied, the same film can be used for reproducible measurements for several days.     

Voltammetric Behavior of Osmium‐Labeled DNA at Mercury Meniscus‐Modified Solid Amalgam Electrodes. Detecting DNA Hybridization

The complex of osmium tetroxide with 2,2′‐bipyridine has been utilized as a probe of DNA structure and an electroactive marker of DNA in DNA hybridization sensors. It produces several voltammetric signals, the most negative of them has been observed only at mercury electrodes. This signal is of catalytic nature affording a high sensitivity of DNA determination. The catalytic current due to evolution of hydrogen in voltammetry of DNA modified by complex of osmium tetroxide with 2,2′‐bipyridine (DNA‐Os,bipy) was studied. Solid amalgam electrodes (modified with mercury menisci) of silver (m‐AgSAE), copper (m‐CuSAE), gold, and of combined bismuth and silver, were used as possible substitutes for mercury electrodes. Besides the hanging mercury drop electrode (HMDE), the catalytic current was observed only on m‐AgSAE and m‐CuSAE. Electrodes of gold and bismuth amalgams did not give the catalytic current. The detection limit of DNA‐Os,bipy on HMDE was 0.1 ng mL^?1 (RSD=2.3 %, N=11), and on m‐AgSAE 0.2 ng mL^?1 (RSD=3.1%, N=11). The m‐AgSAE was successfully applied as a detection electrode in double‐surface DNA hybridization experiments offering highly specific discrimination between complementary (target) and nonspecific DNAs, as well as determination of the length of a repetitive DNA sequence. The m‐AgSAE has proved a convenient alternative to the HMDE or carbon electrodes used for similar purposes in previous work.     

银电极在电化学分析研究中的应用

银电极（包括裸银电极、修饰银电极）因其特有的物理化学性质和电化学性能,被广泛用于伏安分析、光谱／波谱电化学和压电传感器等电化学分析领域。本文对某在这些领域中的研究和应用进行了综述,引用文献一百余篇。     

Electrochemical Biosensors Based on Enzymatic Reactors Filled by Various Types of Silica and Amalgam Powders for Measurements in Flow Systems

Two enzymatic biosensors with amalgam powder reactors and twelve enzymatic biosensors with various silica powder reactors were fabricated and tested in this work. The enzymatic reactors based on silver amalgam powder provide high sensitivity and they are convenient for faster flow rates. Experiments with six silica materials showed that mesoporous silica SBA‐15 was the best one in terms of covering by enzymes, sensitivity and lifetime of biosensors. The current response of the SBA15‐glucose oxidase (GOx) sensor started to decrease only after 200 day testing and after 406 days the peak current was still 35.9 % of the initial value. The used amalgam tubular detector in a flow system allowed working at highly negative potentials, which significantly increased the sensitivity of determinations. Statistical results of parallel measurement of model solutions with the fabricated biosensors show their high accuracy (RSD=0.28–1.81 %) and sensitivity (6.2–14.3 µmol L^?1). The proposed SBA15‐GOx biosensor was successfully used for determination of glucose in commercial honey.     

Selective Electrochemical Detection of Explosives with Nanomaterial Based Electrodes

Explosive detection technologies play a critical role in maintaining national security, remain an active research field with many devices and analytical/electroanalytical techniques. Analytical chemistry needs for homeland defense against terrorism make it clear that real-time and on-site detection of explosives and chemical warfare agents (CWAs) are in urgent demand. Thus, current detection techniques for explosives have to be improved in terms of sensitivity and selectivity, opening the way to electrochemical devices suitable to obtain the targeted analytical information in a simpler, cheaper and faster way. For the electrochemical determination of energetic substances, a large number of sensor electrodes have been presented in literature using different modification materials, especially displaying higher selectivity with molecularly imprinted polymers (MIPs). MIPs have already been utilized for the detection of hazardous materials due to their mechanical strength, flexibility, long-time storage and low cost. The sensitivity of MIP-based electrosensors can be enhanced by coupling with nanomaterials such as graphene oxide (GOx), carbon nanotubes (CNTs), or nanoparticles (NPs). Specific characteristics of involved nanomaterials, their modification, detection mechanism, and other analytical aspects are discussed in detail. Non-MIP electrosensors are generally functionalized with materials capable of charge transfer, H-bonding or electrostatic interactions with analytes for pre-concentration and electrocatalysis on their surface, whereas nanobio-electrosensors use analyte-selective aptamers having specific sequences of DNA, peptides or proteins to change the potential or current. This review intends to provide a combination of information related to MIPs and nanomaterial-based electrochemical sensors, limited to the most significant and illustrative work recently published.     

Combined Voltammetric‐Potentiometric Sensor with Silver Solid Amalgam Link for Electroanalytical Measurements

An arrangement of a combined voltammetric‐potentiometric sensor (CVPS) with a silver solid amalgam link (AgSAL) was designed, comprising a working electrode inserted into an internal solution of a proper depolarizer (e.g., 10 ppm Cu(II) in 0.2 M acetate buffer, 2% tartaric acid), which is separated from the analyzed solution by the AgSAL or other amalgam links. The preparation procedure of the AgSAL was described. The sensor has been successfully tested using solutions at various concentrations of Ag(I) and Hg(II) in various types of base electrolytes, exhibiting good selectivity with respect to Ag(I) or Hg(II) ions. The proportional voltammetric current concentration dependences i_p?ln c were obtained and interpreted.     

Characterization of Carbon Film Electrodes for Electroanalysis by Electrochemical Impedance

The interfacial behavior of electrodes fabricated from carbon film resistors of 2 and 20 Ω in supporting electrolyte solutions of varying pH used in electroanalytical experiments has been characterized by electrochemical impedance spectroscopy with complementary cyclic voltammetric experiments. Equivalent circuits are proposed to fit the experimental data and the influence of electrode pretreatment has also been investigated.     

Tubular Detector of Silver Solid Amalgam for Electrochemical Measurements in Flow Systems

This paper presents the application of the tubular detector based on silver solid amalgam (TD‐AgSA) for electrochemical determinations of reducible inorganic (Cd²⁺, Zn²⁺) and organic (4‐nitrophenol) compounds under flow injection analysis conditions. The newly developed TD‐AgSA is simple, robust and inexpensive. The limits of detections of Zn²⁺, Cd²⁺ and 4‐nitrophenol are 1.4×10^?6, 7.0×10^?7, and 5.0×10^?7 mol dm^?3, respectively (i.e. 0.09, 0.08 and 0.07 ppm). The obtained results proved the long‐term stability of the detector (RSD of the determination of Zn²⁺, Cd²⁺, and 4‐nitrophenol were 0.8, 0.9 and 0.8 % (n=10; c_Zn=7.7×10^?5 mol dm^?3, c_Cd=4.5×10^?5 mol dm^?3 and c_4‐NPh=3.6×10^?5 mol dm^?3), respectively and its applicability for cathodic measurements in aqueous solutions at potentials up to ?2 V.     

Voltammetric Determination of Azidothymidine Using Silver Solid Amalgam Electrodes

A new simple and direct electroanalytical method was developed for the determination of azidothymidine in commercial pharmaceutical preparations. It is based on differential pulse voltammetry at silver solid amalgam electrode with polished surface (p‐AgSAE) or surface modified by mercury meniscus (m‐AgSAE). The electroreduction of azidothymidine in basic media at these electrodes gives rise to one irreversible cathodic peak. Its potential in 0.05 mol L^?1 borate buffer, pH 9.3 at ca. ?1050 mV is comparable to that using hanging mercury drop electrode (HMDE). Achieved limits of quantitation are in the 10^?7 mol L^?1 concentration range for both amalgam electrodes. According to the procedure based on the standard addition technique, the recoveries of known amounts of azidothymidine contained in pharmaceutical preparations available in capsules were 101.4±1.8% (m‐AgSAE), 100.3±3.5% (p‐AgSAE) and 102.0±1.0% (HMDE) (n=10). There was no significant difference between the values gained by proposed voltammetric methods and the HPLC‐UV recommended by the United States Pharmacopoeia regarding the mean values and standard deviations.     

Critical Impact of Chloride Containing Reference Electrodes on Electrochemical Measurements

Chloride containing reference electrodes, such as various silver‐silver chloride electrodes, are well established in electrochemical analyses. Usually less attention is paid to the influence of potential chloride contamination of electrochemical measurements. Herein, the impact of the chloride leakage rate is studied by means of experiments concerning the anodic oxidation of aluminum. Based on the results, the authors determine critical leakage rates, depending on typical electrolyte volumes and experimental conditions. The results demonstrate that chloride leakage can significantly influence electrochemical measurements, even at ultra‐low leakage rates. A guideline for the usage of chloride containing reference electrodes is deduced from the experimental results and theoretical considerations.     

Electrochemical Behaviour of Benzofuran Derivatives of Pharmaceutical Interest at Solid Electrodes

Abstract

The electrooxidation of four structually related drugs (amiodarone and benziodarone and their iodinated derivatives), has been studied, using cyclic voltammetry and controlled potential coulometry at carbon paste and platinum electrodes in hydro-organic media. The oxidative mechanisms have been suggested on the basis of a comparative study and by analyzing the i_p, E_p/ pH plots, the number of electrons evolved and the cyclic voltammetric behaviours. The influence of carbon-iodine bonds on the redox pattern of the molecules has been analyzed and a comparison between the oxidation pattern of the phenolic molecules and the corresponding diethylaminoethoxy derivatives has been realized. Quantitative measurements have been obtained at the carbon paste electrode, within the range of concentrations 5. × 10^?6 M - 5 × 10⁵ M. The analytical usefulness in determination of these compounds has been demonstrated.     

Additional Studies on the Electrochemical Behaviour of Three Macrolides on Pt and Carbon Based Electrodes

The voltammetric behaviour of the macrolide based antibiotic: Erythromycin (ERT), Clarithromycin (CLA) and Azithromycin (AZT) was presented in this work. Carbon electrodes and platinum (Pt) electrode were applied as working electrodes. Cyclic voltamograms of each molecule in each electrode were recorded and similar electrochemical behaviour of macrolides was observed for all carbon based electrodes, which gave more defined current intensity peaks than platinum. Other organic compounds were tested trying to clarify electro-active groups of macrolides. Experiments on mechanism of electrochemical reaction were performed, and studies on the influence of pH on peak current and peak potential were also carried out.     

双硫腙修饰固体银汞合金电极吸附伏安法测定痕量铅

制作了银汞合金电极,在其表面用双硫腙进行修饰,溶液中铅离子与电极表面的双硫腙发生螯合作用被富集。当电极电位在-0.20~-0.70V间进行阴极化扫描时,配合物中铅离子在电极表面被还原,于-0.40V左右形成灵敏的还原峰。选择了反应介质并优化了pH值、双硫腙用量、富集时间等实验参数。利用该修饰电极测定铅的线性范围为0.02~1.2mg/L,检出限为10μg/L。对0.6mg/L Pb2 溶液进行11次平行测定,相对标准偏差为4.1%。该法用于实际水样铅的测定,回收率为94.8%。     

Fabrication of Au‐Nanoparticle/TiO2‐Nanotubes Electrodes Using Electrochemical Methods and Their Application for Electrocatalytic Oxidation of Hydroquinone

Gold nanoparticle (Au‐NPs)‐Titanium oxide nanotube (TiO₂‐NTs) electrodes are prepared by using galvanic deposition of gold nanoparticles on TiO₂‐NTs electrodes as support. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy results indicate that nanotubular TiO₂ layers consist of individual tubes of about 60–90 nm diameters and gold nanoparticles are well‐dispersed on the surface of TiO₂‐NTs support. The electrooxidation of hydroquinone of Au‐NPs/TiO₂‐NTs electrodes is investigated by different electrochemical methods. Au‐NPs/TiO₂‐NTs electrode can be used repeatedly and exhibits stable electrocatalytic activity for the hydroquinone oxidation. Also, determination of hydroquinone in skin cream using this electrode was evaluated. Results were found to be satisfactory and no matrix effects are observed during the determination of hydroquinone content of the “skin cream” samples.     

基于碳纳米管的化学修饰电极及电化学生物传感器的研究进展

综述了碳纳米管的结构、合成、纯化、功能化、分散及基于碳纳米管的化学修饰电极和电化学生物传感器的研究进展。     

Electrochemical Determination of Anti-Hyperlipidemic Drug Ezetimibe Based on its Oxidation on Solid Electrodes

Ezetimibe is the first of a new class of drugs that selectively inhibits cholesterol absorption in the small intestine and reduces plasma LDL cholesterol. In this study, electrochemical oxidation of ezetimibe was investigated on carbon based electrodes and a single and irreversible peak at both electrodes was observed. A linear response was detected between 2 × 10^?6 and 8 × 10^?5 M with glassy carbon electrode and between 2 × 10^?6 and 2 × 10^?4 M with a boron-doped diamond electrode in 0.1 M H₂SO₄ supporting electrolyte. The proposed methods were successfully applied for the determination of ezetimibe from pharmaceutical dosage forms and human serum samples.