Solid Amalgam Research Articles

Application of renewable silver amalgam annular band electrode to voltammetric determination of vitamins C, B1 and B2

In this work, the design and results of applying silver liquid amalgam film–modified silver solid amalgam annular band electrode (AgLAF–AgSAE), refreshed before each measurement, to voltammetric determination of vitamins C (VC), B1 (VB1) and B2 (VB2) are presented. The method is based on adsorptive accumulation of analytes at the AgLAF–AgSAE in a phosphate buffer (VB1), phosphate buffer with Triton X-100 (VB2) and an alkaline borate buffer with Triton X-100 (VC). The analytical parameters and procedure of electrode activation were optimized. The calibration graphs obtained for vitamins C, B1 and B2 are linear, respectively, for concentration range 0.05–12, 0.01–0.1 and 0.05–3mgL−1. The detection limits were calculated and equaled 0.02, 0.003 and 0.009mgL−1, while repeatability of the peak current was 2%, 1% and 3%, respectively. These results are comparable with results obtained for polarographic determination of the same vitamins using mercury electrodes. Finally, the AgLAF–AgSAE was applied to the determination of vitamins in pharmaceutical samples and fruit juices with satisfactory results.

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.

A Comparative Electrochemical Behaviour Study and Analytical Detection of the p-Nitrophenol Using Silver Solid Amalgam, Mercury, and Silver Electrodes

This work reports a comparative electrochemical behaviour study and p-nitrophenol analytical detection using silver solid amalgam, hanging dropping mercury, and silver electrodes. For this, square wave voltammetry was employed, where the analytical responses and the redox mechanisms could be compared for reduction processes of 4-nitrophenol by analysis of the voltammetric responses. The analytical performance of the electrode was evaluated and detection and quantification limits, recovery percentages, repeatability, and reproducibility for the silver solid amalgam and hanging dropping mercury electrodes presented similar values; the results presented for the silver electrode indicated worse analytical parameters than the other electrodes. The results indicate that the silver solid amalgam electrode can be considered a suitable tool and an interesting alternative for the analytical determination of 4-nitrophenol, as well as for the determination of other biological and environmentally interesting compounds that present analytical responses on mercury surfaces.

Voltammetric determination of 6-nitrobenzimidazole in the presence of surfactants

Determination of 6-nitrobenzimidazole by differential pulse voltammetry at a hanging mercury drop electrode, a polished silver solid amalgam electrode and a mercury meniscus modified silver solid amalgam electrode was studied in the presence of the surfactants Triton X-100, cetyltrimethylammonium bromide and sodium dodecyl sulfate. It was found that only cetyltrimethylammonium bromide at polished silver solid amalgam electrode increases the voltammetric signal. This fact was used for the determination of 6-nitrobenzimidazole in the concentration range from 1 × 10–7 to 1 × 10–4 mol l–1 by differential pulse voltammetry at polished silver solid amalgam electrode in the presence of cetyltrimethylammonium bromide (concentration 1 × 10–4 mol l–1).

Electrocatalytic detection of polysaccharides at picomolar concentrations

Electroinactive polysaccharides (PS) modified by osmium(VI) complexes with nitrogenous ligands produce redox couples at carbon and mercury electrodes. We show that PS adducts with Os(VI) 2,2'-bipyridine produce at ~-1.2 V (against Ag/AgCl/3 M KCl electrode) an additional peak at mercury and solid amalgam electrodes. This peak is due to the catalytic hydrogen evolution, allowing detection of PS (such as dextran and mannan) at picomolar concentrations.

Utilização de eletrodos sólidos de amálgama para a determinação analítica de compostos orgânicos e inorgânicos

This review reports the use of solid amalgam electrodes in the electroanalytical determination of organic and inorganic compounds. The different types of amalgam electrodes are presented, and attention is paid to solid amalgam electrode, and here is presented details about the pre-treatment for activation and renovation and also possible modifications in its surface. The wide potential range, higher signal-to-noise ratio, mechanical stability enabling their application in flowing systems, and principally their resistance toward passivation, indicate that the solid amalgam electrodes are environmentally friendly alternatives to mercury electrodes, without loss in the sensitivity and reproducibility in voltammetric responses.

Voltammetric Determination of Selected Nitro Compounds at a Polished Silver Solid Amalgam Composite Electrode

AbstractVoltammetric behavior of selected biologically active organic nitro compounds, namely 2‐nitrofluorene, picric acid (2,4,6‐trinitrophenol) and metronidazole, has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam composite electrode (p‐AgSA‐CE). The optimum conditions have been found for their determination in a 1 : 1 mixture of methanol and aqueous Britton–Robinson buffer of pH 5.0 for 2‐nitrofluorene and in the aqueous Britton–Robinson buffer solutions of pH 2.0 and 4.0 for picric acid and metronidazole, respectively, with the limits of quantification (LQs) 4, 0.1 and 2 µmol L−1 (DCV at p‐AgSA‐CE) and 3, 1 and 4 µmol L−1 (DPV at p‐AgSA‐CE) for 2‐nitrofluorene, picric acid and metronidazole, respectively. An attempt to increase the sensitivity using adsorptive stripping voltammetry was not successful for all three test substances. For comparison, the UV‐vis spectrophotometric determinations of studied compounds have also been carried out in methanol for 2‐nitrofluorene (LQ≈1 µmol L−1) and in deionized water for picric acid (LQ≈3 µmol L−1) and metronidazole (LQ≈2 µmol L−1). Practical applicability of the newly developed voltammetric methods was verified on direct determination of the studied compounds in drinking and river waters with LQs around 10−6 mol L−1 for all the studied compounds.

Electrochemical behavior of folic acid on mercury meniscus modified silver solid amalgam electrode

Voltammetric behavior of folic acid and folates has been investigated using direct current voltammetry, differential pulse voltammetry and adsorptive stripping differential pulse voltammetry at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE). The optimum conditions have been found for their determination in a 1:9 mixture of methanol and aqueous acetate buffer, with the limit of detection about 0.5nmolL−1. RSD at this concentration level amounted to less than 4%. Practical applicability of the newly developed method was verified by analysis of three vitamin preparations and of two multivitamin juices.

A novel paste electrode based on a silver solid amalgam and an organic pasting liquid

The silver solid amalgam fine powder mixed with a proper pasting liquid, firstly introduced in this work, was found to be a new suitable electrode material for sensitive voltammetric determination of electrochemically reducible organic compounds. The optimal composition of the amalgam (mercury/silver ratio) and the formed paste (i.e., quality and quantity of pasting liquid and its ratio relative to amalgam) was tested by modern voltammetric methods using 4-nitrophenol as a model compound. This new non-toxic electrode material combines the advantages of an easily renewable paste electrode surface solving the problems connected with the passivation of the solid electrodes and of amalgam electrodes providing good mechanical stability, simple handling and preparation, wide potential window in cathodic potential range and sufficient sensitivity. The silver amalgam fine powder prepared in the weight ratio 60/40 (Hg/Ag) mixed with paraffin oil in the weight ratio 20:1 (w/w) was found to be the most convenient for the determination of 4-nitrophenol using differential pulse voltammetry with limit of detection 1 μmol l −1 in 0.2 mol l −1 acetate buffer pH 4.8.

The effect of composition of solid silver amalgam electrodes on their electrochemical response

The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed that the AgSAE 30/70 contained only one single phase (Ag2Hg3), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III) chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes.

Voltammetric Behavior of Methotrexate Using Mercury Meniscus Modified Silver Solid Amalgam Electrode

AbstractVoltammetric behavior of methotrexate (MTX), an important chemotherapeutic drug, has been investigated using electrochemical methods: cyclic voltammetry, direct current voltammetry and differential pulse voltammetry on a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE). The obtained results have been compared with those obtained using a hanging mercury drop electrode (HMDE). The optimal conditions for its determination have been found in a Britton‐Robinson buffer of pH 5 with the limit of detection equal to 1.8 nM. RSD at this concentration level amounted to less than 4 %. The proposed procedure of determination was verified on a real drug containing MTX.

Facile end-labeling of RNA with electroactive Os(VI) complexes

Ribose at the 3′-end of oligonucleotides (oligos) selectively modified by Os(VI)2,2′-bipyridine (bipy) produced two CV redox couples at pyrolytic graphite electrode. Using square wave voltammetry (SWV) 22-mer oligos can be detected down to 250 nM. At mercury electrodes the Os(VI)bipy-oligo adducts produced an electrocatalytic peak at ~−1.2 V allowing their determination down to picomolar concentrations. High specificity of Os(VI)bipy for ribose in nucleic acids and high sensitivity of the determination at mercury and solid amalgam electrodes give promise for new efficient methods of microRNA determination.

Preparation and Properties of Mercury Film Electrodes on Solid Amalgam Surface

AbstractA simple apparatus (electrolyzer) and a reliable procedure were developed for the preparation of mercury films of exactly defined thickness on a silver solid amalgam substrate. Constant concentration of Hg(II) in the electrolyzer is ensured by dissolution of an anode from silver paste amalgam. Small volume of electrolyte, which can be used repeatedly many times, and paste amalgam preventing the spillage of liquid mercury substantially decrease the danger of environmental contamination with mercury. Parameters and behavior of mercury film electrodes on silver solid amalgam substrate (MF‐AgSAE) were compared with polished silver solid amalgam electrode (p‐AgSAE) which does not contain liquid mercury, with mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and with hanging mercury drop electrode (HMDE). The height of anodic stripping voltammetric peaks divided by electrode area was highest for MF‐AgSAE and the width of those peaks, which determines the resolution of the method, was minimal at MF‐AgSAE. Available potential window of MF‐AgSAE in different supporting electrolytes is comparable with that of HMDE.

Voltammetric Determination of Genotoxic Nitro Derivatives of Fluorene and 9‐Fluorenone Using a Mercury Meniscus Modified Silver Solid Amalgam Electrode

AbstractVoltammetric behavior of selected genotoxic nitro compounds (2‐nitrofluorene, 2,7‐dinitrofluorene, 2‐nitro‐9‐fluorenone and 2,7‐dinitro‐9‐fluorenone) has been investigated using direct current voltammetry (DCV), differential pulse voltammetry (DPV) and adsorptive stripping differential pulse voltammetry (AdSDPV) at a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE). The optimum conditions have been found for their determination in a 1 : 1 mixture of methanol and aqueous Britton–Robinson buffer solution, with the limits of quantification, (LOQ), 2, 0.3, 0.5, and 0.5 μmol L−1 (DCV at m‐AgSAE) and 0.2, 0.2, 0.4, and 0.2 μmol L−1 (DPV at m‐AgSAE) for 2‐nitrofluorene, 2,7‐dinitrofluorene, 2‐nitro‐9‐fluorenone, and 2,7‐dinitro‐9‐fluorenone, respectively. An attempt at increasing the sensitivity using AdSDPV at m‐AgSAE was successful only for 2‐nitrofluorene (LOQ=2 nmol L−1). Practical applicability of the newly developed methods was verified on direct determination of the studied compounds in drinking and river waters with LOQs ~ 10−7 mol L−1 for all the studied compounds.

Voltammetric Determination of Aliphatic Phthalate Esters at a Hanging Mercury Drop Minielectrode and a Meniscus Modified Silver Solid Amalgam Electrode

AbstractA new simple, fast and sensitive differential pulse voltammetric method was developed for the determination of different aliphatic phthalates. Dibutyl phthalate, diethyl phthalate, didecyl phthalate, and diallyl phthalate can be determined in 0.1 M tetramethylammonium bromide in methanol using a hanging mercury drop minielectrode and a meniscus modified silver solid amalgam electrode. Optimum conditions were found including concentration and composition of supporting electrolyte and solvent, scan rate, pulse amplitude, pulse width, etc. Linear calibration curves were obtained for 10−5 and 10−6 M and for hanging mercury drop minielectrode also for 10−7 M.

Voltammetric determination of ketoconazole using a polished silver solid amalgam electrode

This paper describes the use of a polished silver solid amalgam electrode (p-AgSAE), evaluation of its electrochemical behaviour and the development of an electroanalytical procedure for the determination of ketoconazole (KC) in pharmaceutical formulations. The experimental and voltammetric conditions were evaluated and the best responses were obtained in BR buffer (pH 12.0) with f = 100 s −1, a = 25 mV and ΔE s = 2 mV. Under these conditions, the voltammetric response of KC presented a well-defined and quasi-reversible reduction peak at around −1.46 V vs. Ag/AgCl/Cl − at 3.0 mol L −1. Analysis of a purified laboratory electrolyte using the proposed methodology allowed for responses that were directly proportional to KC concentration, and the analytical sensitivity was comparable to published results using mercury electrodes and solid surfaces, such as carbon paste, gold and platinum electrodes. The recovery percentages in pure electrolyte, as well as tablet, shampoo and cream samples, showed values from 90 to 105%, demonstrating that the voltammetric methodology proposed is suitable for determining KC in complex samples. The method has excellent robustness and specificity for analytical purposes, minimises toxic residues due to the use of liquid mercury, and avoids adsorptive processes related to the use of other solid surfaces.

Rapidly renewable silver amalgam annular band electrode for voltammetry and polarography

This work describes a novel type of working electrode for use in voltammetry and polarography — the renewable silver liquid amalgam film–modified silver solid amalgam annular band electrode (AgLAF–AgSAE). The electrode is produced by mechanically refreshing the silver liquid amalgam film (AgLAF) before each measurement. The main constituents of the electrode are: a specially constructed silver solid amalgam annular band electrode (AgSAE), two silicon O-rings, silver liquid amalgam and a polypropylene electrode body. Contaminants from the analyzed solution are removed and the AgSAE surface is covered with a thick layer of fresh amalgam while pulling the AgSAE into the sensor body. During movement in the reverse direction AgLAF is formed and homogenized. The time needed to refresh the film is less than 1 s. The electrode is characterized by excellent surface repeatability (∼ 1%) and long-term stability (over ten thousand measurement cycles).

Fabrication and Characterization of Solid Mercury Amalgam Electrodes for Protein Analysis

Gold and carbon electrodes have been largely used as transducers in protein and DNA sensors and arrays. Liquid mercury electrodes, with potential windows allowing detection of DNA and protein reduction processes at highly negative potentials, were considered as useless in such arrays. Here, we show that solid amalgam electrode (SAE) arrays can be prepared as a substitution of liquid mercury in the analysis of the above biomacromolecules. Vacuum metal sputtering on a glass substrate, photolithography, and galvanic mercury amalgam formation were used for fabrication of an inexpensive disposable electrode array. The resulting ultrathin (less than 1 microm) amalgam microelectrodes were characterized with respect to influence of the electrode composition and size on the reproducibility and stability of electrochemical signals. Further characterization was performed using electron microscopy and the well-established ruthenium electrochemistry. Final, optimized, design was applied in protein analysis employing the recently described electrocatalytic chronopotentiometric peak H.

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

AbstractIn 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).