Amalgam Electrode Research Articles

Electrochemical detection of 5-methylcytosine in bisulfite-treated DNA

DNA methylation is an important epigenetic event playing crucial roles in physiologic and pathologic processes. We show that methylation of cytosine (C) residues in DNA can be easily detected electrochemically using mercury or solid amalgam electrodes. Reduction peaks of untreated single-stranded methylated and non-methylated oligodeoxynucleotides (ODN) do not significantly differ. Using DNA bisulfite treatment, reducible Cs are transformed into nonreducible uracil residues, strongly decreasing square wave voltammetric C reduction peaks. On the other hand, 5-methylcytosine (mC) residues resist the bisulfite treatment and display almost unchanged reduction peak. Desulfonation step should be omitted because uracil sulfonation improves the resolution of C from mC. By combining DNA bisulfite treatment with square wave voltammetry, DNA methylation can be determined quantitatively at nanomolar and subnamolar ODN concentrations.

Voltammetric monitoring of electrochemical reduction of riboflavin using silver solid amalgam electrodes

The voltammetric behavior of riboflavin (RF), an important compound belonging to the group of vitamins B, has been investigated using mercury meniscus modified electrode (m-AgSAE) and polished silver solid amalgam electrode (p-AgSAE). Obtained results were compared with those obtained using hanging mercury drop electrode (HMDE). Cyclic voltammetry (CV), direct current voltammetry (DCV) and differential pulse voltammetry (DPV) have been applied for investigation of electrochemical behavior of RF on the above mentioned electrodes. Optimum conditions for DPV determination of RF have been found in acetate buffer of pH 5 for m-AgSAE and HMDE, and in Britton–Robinson (BR) buffer of pH 3 for p-AgSAE. The limits of detection amounted to 8.2×10−10molL−1 (m-AgSAE) and 1.3×10−9molL−1 (p-AgSAE). DPV with optimized parameters was utilized for successful determination of RF in 2 vitamin preparations.

Ninety Years of Polarography

Ninety Years of Polarography

Electrocatalysis in proteins, nucleic acids and carbohydrates

The ability of proteins to catalyze hydrogen evolution has been known for more than 80 years, but the poorly developed d.c. polarographic "pre-sodium wave" was of little analytical use. Recently, we have shown that by using constant current chronopotentiometric stripping analysis, proteins produce a well-developed peak H at hanging mercury drop and solid amalgam electrodes. Peak H sensitively reflects changes in protein structures due to protein denaturation, single amino acid exchange, etc. at the picomole level. Unmodified DNA and RNA do not yield such a peak, but they produce electrocatalytic voltammetric signals after modification with osmium tetroxide complexes with nitrogen ligands [Os(VIII)L], binding covalently to pyrimidine bases in nucleic acids. Recently, it has been shown that six-valent [Os(VI)L] complexes bind to 1,2-diols in polysaccharides and oligosaccharides, producing voltammetric responses similar to those of DNA-Os(VIII)L adducts. Electrocatalytic peaks produced by Os-modified nucleic acids, proteins (reaction with tryptophan residues) and carbohydrates are due to the catalytic hydrogen evolution, allowing determination of oligomers at the picomolar level.

Simple protein structure-sensitive chronopotentiometric analysis with dithiothreitol-modified Hg electrodes

We have shown that proteins produce at bare mercury electrodes a well-developed chronopotentiometric peak H. At sufficiently high current densities and low ionic strengths, this peak is sensitive to changes in protein structures. At higher ionic strengths this sensitivity can be lost but it can be restored, when instead of bare, thiol-modified Hg electrodes are used. Here we studied properties of the dithiothreitol (DTT) layer at the hanging mercury drop electrode and showed that at low concentrations (5μM–200μM) the DTT is adsorbed as a dithiol with both –SH groups attached to the surface. At higher DTT concentrations than 1mM, a densely packed pinhole-free layer is formed with the DTT molecules bound to the electrode surface by a single –SH group, oriented perpendicularly to the surface. We found that, if a sufficiently high DTT concentration is used, preparation of the DTT-modified Hg electrodes can be omitted and proteins can be co-adsorbed with DTT on liquid Hg or solid amalgam electrodes without the loss of sensitivity for changes in protein structures. The newly observed properties of the DTT self assembled monolayers (SAMs) at Hg electrodes appear important for designing new types of solid amalgam electrode arrays for electrochemical analysis of proteins.

The use of silver solid amalgam electrodes for voltammetric and amperometric determination of nitrated polyaromatic compounds used as markers of incomplete combustion.

Genotoxic nitrated polycyclic aromatic hydrocarbons (NPAHs) are formed during incomplete combustion processes by reaction of polycyclic aromatic hydrocarbons (PAHs) with atmospheric nitrogen oxides. 1-Nitropyrene, 2-nitrofluorene, and 3-nitrofluoranthene as the dominating substances are used as markers of NPAHs formation by these processes. In the presented study, voltammetric properties and quantification of these compounds and of 5-nitroquinoline (as a representative of environmentally important genotoxic heterocyclic compounds) have been investigated using a mercury meniscus modified silver solid amalgam electrode (m-AgSAE), which represent a nontoxic alternative to traditional mercury electrodes. Linear calibration curves over three orders of magnitude and limits of determination mostly in the 10−7 mol L−1 concentration range were obtained using direct current and differential pulse voltammetry. Further, satisfactory HPLC separation of studied analytes in fifteen minutes was achieved using 0.01 mol L−1 phosphate buffer, pH 7.0 : methanol (15 : 85, v/v) mobile phase, and C18 reversed stationary phase. Limits of detection of around 1 · 10−5 mol L−1 were achieved using amperometric detection at m-AgSAE in wall-jet arrangement for all studied analytes. Practical applicability of this technique was demonstrated on the determination of 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, and 5-nitroquinoline in drinking water after their preliminary separation and preconcentration using solid phase extraction with the limits of detection around 1 · 10−6 mol L−1.

Voltammetric determination of 2-amino-6-nitrobenzothiazole at two different silver amalgam electrodes

Voltammetric behavior of genotoxic 2-amino-6-nitrobenzothiazole (ANBT) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p-AgSAE) and at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE). The optimum conditions have been found for its determination in the concentration range of 0.2–100 μmol l −1 in a 9:1 (v/v) mixture of aqueous Britton–Robinson buffer solution (pH 10.0) and methanol, with the limits of quantification ( L Qs) 0.10 μmol l −1 (DCV at p-AgSAE), 0.19 μmol l −1 (DPV at p-AgSAE), 0.17 μmol l −1 (DCV at m-AgSAE) and 0.12 μmol l −1 (DPV at m-AgSAE). An attempt at increasing the sensitivity using adsorptive stripping DCV or DPV at both p-AgSAE and m-AgSAE was not successful. Practical applicability of the newly developed methods was verified on direct determination of ANBT in spiked samples of drinking and river water, with L Qs ∼ 10 −7 mol l −1.

Advantages and Progress in the Analysis of DNA by Using Mercury an Amalgam Electrodes - Review

Advantages and Progress in the Analysis of DNA by Using Mercury an Amalgam Electrodes - Review

Advantages and Progress in the Analysis of DNA by Using Mercury an Amalgam Electrodes - Review

Advantages and Progress in the Analysis of DNA by Using Mercury an Amalgam Electrodes - Review

Voltammetric determination of leucovorin using silver solid amalgam electrode

The voltammetric behavior of leucovorin (LV), as an important and stable reduced metabolite of folic acid, has been investigated on polished (p-AgSAE) and mercury meniscus modified (m-AgSAE) silver solid amalgam electrodes in this paper. LV, after its reverse electrochemical oxidation, can be reduced in two reduction steps in an acidic medium on both electrodes used. The first reduction peak ( E p = −400 mV) can be used for determination of LV. Differential Pulse Voltammetry (DPV) was applied for monitoring voltammetric behavior of LV on both working electrodes. Elimination voltammetry with linear scan was applied for elucidation of the reaction mechanisms. The limits of detection were calculated as 2.2 × 10 −8 mol L −1 ( t acc = 60 s) for m-AgSAE and 5.0 × 10 −8 mol L −1 ( t acc = 100 s) for p-AgSAE. The proposed method was applied for LV determination in the pharmaceutical preparation which has been commonly used during methotrexate therapy.

Voltammetric and amperometric determination of selected dinitronaphthalenes using single crystal silver amalgam based sensors

Modern voltammetric techniques, combined with the quasi-cylindrical single crystal silver amalgam electrode (CAgAE) tested, were used for determination of selected environmental pollutants, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene and 1,8-dinitronaphthalene. The optimum conditions were found for the determination of selected dinitronaphthalenes (DNNs) using direct current voltammetry and differential pulse voltammetry. The procedures were applied to determination of these analytes in model samples of tap water. The 1,3-, 1,5- and 1,8-DNN were determined by differential pulse voltammetry (DPV) with limits of quantification 1.0, 1.0 and 0.3μmoll−1 in concentration range up to 100μmoll−1 in Britton–Robinson buffer and methanol mixture (1:1) with final pH 8.2, 12.3 and 8.2, respectively. The 1,3-, 1,5- and 1,8-DNN were then determined by DPV with limits of quantification 0.4, 0.5 and 0.4μmoll−1 in model samples of tap water conditioned by Britton–Robinson buffer (9:1) pH 7.0, 12.0 and 7.0, respectively, in presence of 0.001moll−1 Na2EDTA. Adsorptive stripping differential pulse voltammetry was unsuccessfully tested in an attempt to obtain lower limits of quantification. The processes occurring during the DNNs reduction at the CAgAE were also investigated by cyclic voltammetry. A single crystal of the silver amalgam was then used to design a cylindrical flow-through detector which was utilized for amperometric detection of selected DNNs in a mixture, after their separation by conventional HPLC. The optimum separation and detection conditions for the DNNs at the cylindrical flow-through detector were found. The DNNs were separated using column with reverse phase C-18, ammonium acetate pH 4.7–methanol (27:73) as mobile phase at flow rate 1.5mlmin−1 and detected by the cylindrical detector at potential −1.2V with limit of detection 1μmoll−1 within concentration range up to 100μmoll−1. Single-crystal silver amalgam was found to be a suitable alternative for “toxic” mercury in voltammetric measurements and a convenient electrode material for designing a new amperometric detector.

Amalgam Electrodes in Organic Electrochemistry

This review with 119 references describes applications of amalgam electrodes in organic electrochemistry. Possible detection arrangements and useful techniques utilizing voltammetric and amperometric methods are briefly discussed. However, main attention is paid to the description of mechanisms of electrode reactions of investigated organic compounds determined at amalgam electrodes during last ten years. Selected derivatives of aromatic hydrocarbons, azo dyes, herbicides, pharmaceuticals, vitamins and biomolecules (e.g. amino acids, peptides, nucleobases and/or nucleic acids) are discussed. The understanding of the discussed methods gives a reader an overview of application possibilities offered by modern electroanalytical methods using amalgam electrodes.

Maximum surface tension and optimum surface electron density

Following the fundamental principle of minimum potential energy and using the notion of the partial charge transfer for halide ions adsorption on mercury, gallium and amalgam electrodes, we have introduced the notion of the “optimum surface electron density”. It corresponds to maximums of electrocapillary curves of mercury-like metals at zero charge potentials in surface inactive electrolytes. Any reversible adsorption of surface active substances violates the optimum surface electron density and consequently decreases and shifts the electrocapillary maximum.

Preparation and Properties of Reference Electrodes Based on Silver Paste Amalgam

AbstractThe preparation and testing of saturated calomel electrodes (SCE‐AgPA), mercury‐mercurous sulfate (MMSE‐AgPA) and mercury‐mercuric oxide (MMOE‐AgPA) reference electrodes based on silver paste amalgam are described. All three electrodes have shown long‐term stability of their potentials (ESCE‐AgPA=−0.56±0.34 mV; EMMSE‐AgPA=391.5±1.4 mV; EMMOE‐AgPA=−104.9±0.7 mV vs. classical SCE; test time was 14 months). All paste amalgam electrodes have potentials close to their analogues with metallic mercury. They can therefore replace each other without any recalculation. Peak potentials of anodic dissolution of cadmium measured with the SCE‐AgPA and SCE are identical. The greatest resistance to polarization was registered with the SCE‐AgPA and significantly lower with other tested electrodes.

Voltammetric Determination of 4‐Nitrophenol and 5‐Nitrobenzimidazole Using Different Types of Silver Solid Amalgam Electrodes – A Comparative Study

AbstractThe voltammetric behavior of two genotoxic nitro compounds (4‐nitrophenol and 5‐nitrobenzimidazole) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p‐AgSAE), a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and a mercury film modified silver solid amalgam electrode (MF‐AgSAE). The optimum conditions have been evaluated for their determination in Britton‐Robinson buffer solutions. The limit of quantification (LQ) for 5‐nitrobenzimidazole at p‐AgSAE was 0.77 µmol L−1 (DCV) and 0.47 µmol L−1 (DPV), at m‐AgSAE it was 0.32 µmol L−1 (DCV) and 0.16 µmol L−1 (DPV), and at MF‐AgSAE it was 0.97 µmol L−1 (DCV) and 0.70 µmol L−1 (DPV). For 4‐nitrophenol at p‐AgSAE, LQ was 0.37 µmol L−1 (DCV) and 0.32 µmol L−1 (DPV), at m‐AgSAE it was 0.14 µmol L−1 (DCV) and 0.1 µmol L−1 (DPV), and at MF‐AgSAE, it was 0.87 µmol L−1 (DCV) and 0.37 µmol L−1 (DPV). Thorough comparative studies have shown that m‐AgSAE is the best sensor for voltammetric determination of the two model genotoxic compounds because it gives the lowest LQ, is easier to prepare, and its surface can be easily renewed both chemically (by new amalgamation) and/or electrochemically (by imposition of cleaning pulses). The practical applicability of the newly developed methods was verified on model samples of drinking water.

Square Wave Stripping Voltammetry of Unlabeled Single‐ and Double‐Stranded DNAs

AbstractWe show that, in difference to previously applied electrochemical methods working with stationary electrodes, square wave voltammetry produces well‐developed peaks IISW (specific for dsDNA) and IIISW yielded by ssDNA at hanging mercury drop electrode (HMDE) and solid amalgam electrodes (SAEs). Using these peaks various kinds of DNA structural transitions can be studied, including unwinding of dsDNA at negatively charged electrode surfaces. The sensitivity of the DNA analysis is much better than that obtained with guanine oxidation signals at carbon electrodes. Both carbon electrodes and SAEs appear attractive as transducers in label‐free RNA and DNA sensors.

Mass Transport Properties of a Flow-Through Electrolytic Reactor Using Zinc Reduction System

An electrolytic process for the removal of Zn(II) from aqueous solution using a parallel amalgamated copper screens cathode operated in the flow through mode is proposed. The current-potential curves recorded at a rotating amalgamated copper disc electrode were used to determine diffusion coefficient of Zn(II). The performance of electrolytic reactor was investigated by using different flow rates at initial zinc ion concentration(48 mg/L). Taking into account the residential Zn(II) concentration, the best results were obtained for cathode potential of (-1.35 V vs. SCE) at flow rate (320 L/h). Zinc ion concentration was found to decrease from 48 mg/L to 1 mg/L during 120 min. of electrolysis. The experimental data are well correlated in term of Sherwood and Reynolds numbers based on the wire diameter of woven screen for characteristic length .Empirical correlation characterized the mass transport properties of the reactor is: Sh = 8.077 Re0.363.

Properties of thiolate monolayers formed on different amalgam electrodes

Formation and properties of thiol (HS(CH2)10COOH or HS(CH2)10CH3) monolayers were investigated at stationary electrodes based on silver, copper, bismuth and cadmium solid amalgams covered by a mercury meniscus or by a mercury film (m-AgSAE, MF-AgSAE, m-CuSAE, m-BiAgSAE and m-CdSAE). For comparison, parallel experiments were performed at a classical hanging mercury drop electrode (HMDE). Thiol monolayers were prepared at an optimal deposition potential (e.g., for HS(CH2)10COOH Eac=−350mV for HMDE and silver amalgam electrodes, Eac=−750 to −800mV for m-CuSAE and m-BiAgSAE, and Eac=−1050mV for m-CdSAE) at which the formed layers exhibit high density and stability. It was found that the potential of a reductive desorption peak of a thiol monolayer strongly depends on the metal which forms the amalgam (for HS(CH2)10COOH: Ep=−864 to −859mV for HMDE and silver amalgam electrodes, Em-BiAgSAE=−1079mV, Em-CuSAE=−1136mV and Em-CdSAE=−1248mV). This allows to create a stable thiol layer in different potential regions according to its application. The influence of a thiol layer charge on the reduction potential was determined.

Crystallic silver amalgam – a novel electrode material

A crystallic silver amalgam was found to be a suitable working electrode material for voltammetric determination of electrochemically reducible organic nitro-compounds. Optimum conditions for crystal growth were found, the crystal surface was investigated by atomic force microscopy in tapping mode and single crystals were used for the preparation of quasi-cylindrical single crystal silver amalgam electrode (CAgAE). An electrochemical behavior of this alternative electrode material was investigated in aqueous media by direct current voltammetry, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and adsorptive stripping voltammetry (AdSV) using 4-nitrophenol as a model compound. Applicable potential windows of the CAgAE were found comparable with those obtained at a hanging mercury drop electrode, providing high hydrogen overpotential, and polished silver solid amalgam electrode. Thanks to the smooth single crystal electrode surface, the effect of the passivation is not too pronounced, direct DPV determination of 100 μmol l(-1) of 4-nitrophenol at CAgAEs in 0.2 mol l(-1) acetate buffer pH 4.8 provides a RSD around 1.5% (n = 15). DPV calibration curves of 4-nitrophenol are linear in the whole concentration range 1-100 μmol l(-1) with a limit of quantification of 1.5 μmol l(-1). The attempt to increase sensitivity by application of AdSV was not successful. The mechanism of 4-nitrophenol reduction at CAgAE was investigated by CV.

Use of microchip electrophoresis and a palladium/mercury amalgam electrode for the separation and detection of thiols

This paper describes the use of microchip electrophoresis, a palladium decoupler, and a downstream mercury/palladium (Hg/Pd) amalgam working electrode to separate and detect a mixture of thiols. While it is known that palladium forms an amalgam with mercury that enables the selective detection of thiols at a low potential, previous reports have used mercury/gold (Hg/Au) amalgam electrodes and there are no reports of using Hg/Pd electrodes for this purpose. The ability to use a Hg/Pd electrode greatly simplifies the fabrication procedure when a Pd decoupler is used to integrate microchip electrophoresis with electrochemical detection. A detailed comparison was made between the use of Hg/Au and Hg/Pd detection electrodes, with the Hg/Pd electrode having a similar performance in terms of voltammetry, sensitivity, and limit of detection. The resulting palladium decoupler and Hg/Pd electrode were used along with a lengthened serpentine channel to result in the separation and detection of a mixture containing homocysteine, cysteine, glutathione, and N-acetylcysteine. Finally, a microchip device that integrates on-chip pumping and injection valves with the Pd decoupler and Hg/Pd electrode was used to separate and detect glutathione from lysed red blood cells.