Mercury Electrode Research Articles

Adsorption of guanine at the interface electrode-acetic buffer solution and its influence on zinc cation electroreduction

Guanine plays an important role in many biological processes since it constitutes the buildings blocks of DNA and RNA. Solutions of guanine were prepared to cover the range from 5 × 10−5 to 8 × 10−4 M. Adsorption of guanine on a mercury electrode in acetic buffers at pH 4 and pH 6 is described by means of the adsorption isotherms constants calculated from the surface pressure as a function of electrode potential and adsorbate bulk concentration. The adsorption parameters from the double layer were calculated based on the data from the differential capacity–potential curves. The entirely different change in the differential capacity in two applied acetate buffers in the absence of guanine results from different buffer composition, as in a solution with a pH 4 adsorption primarily involves acetic acid molecules, whereas in a buffer with a pH 6-acetate ions. The possibility to accurately determine E max and σ max parameters points to a physical character of guanine adsorption, which must be associated with the fact that adsorbed guanine molecules are vertically or diagonal oriented. Obtained R A (charge transfer resistance at formal potential) changes are minor and comply with changes in ΔE. Therefore, it may be concluded that in the tested range of guanine concentrations, it has no effect on kinetics of zinc cation depolarisation at a mercury electrode both in the buffer with pH 4 and pH 6.

Redox Processes of Guanine Moieties in DNA Heptamers Related to Hydrogen Evolution

AbstractThe paper is focused on the electrochemical investigation of DNA heptamers d(GCXXXGC) with different central triplets of nucleotides (XXX=GAA, AAA, CCC, GGG). On a hanging mercury electrode (HMDE), the reduction peaks of adenine (A) and cytosine (C) moieties are detectable, but those of guanine (G) moieties are covered by an intensive current of hydrogen evolution. Because cyclic voltammetry allows us to monitor only the oxidation processes of the G reduced species, the effect of hydrogen evolution reaction (HER) was studied by means of these anodic signals. For different vertex potentials (from −1.60 V to −1.85 V) and a different number of cycles (1–5), all heptamers in buffered solutions (pH 5.8) were tested and double‐peak G oxidation signals (GI and GII) evaluated. The different structures of the heptamers in solutions are confirmed by NMR spectra. Both the impact of hydrogen evolution into the production of 7,8‐dihydroguanine moieties forming together with hydrogen in negative potentials and the catalytic effect of heptamers on hydrogen evolution are discussed.

Electrochemical sensing of concanavalin A and ovalbumin interaction in solution

In an attempt to develop a label- and reagent-free electrochemical method for the detection of lectin-glycoprotein interactions, we tested lectin-concanavalin A (ConA), glycoprotein-ovalbumin (Ova) and their complex using chronopotentiometric stripping (CPS) analysis and a hanging mercury drop electrode. Incubation of ConA with Ova resulted in an increase of the CPS peak H of the complex as compared to the CPS peaks of individual Ova and ConA proteins. Qualitatively similar results were obtained with other glycoprotein-lectin couples (ConA-RNase B and lectin from Sambucus nigra-fetuin). Using the CPS method, we were able to follow the course of complex formation in solution. Comparable responses of Ova, ConA and ConA-Ova complex were obtained not only at the mercury electrode but also with solid amalgam electrodes, which are more suitable for parallel analysis. It can be anticipated that electrochemical methods, namely CPS, will find application in glycomics and proteomics.

Investigation of The Electrode Pathway of Quinoline Azo Dye Compound via Convolutive Voltammetry and Digital Simulation

The electrochemical behavior and the electrode reaction of quinolone azo dye compound was investigated using convolutive cyclic voltammetry at mercury electrode in 50% (v/v) ethanolic Britton-Robinson solutions of pH 2.5 – 12.0. Four electrons slow reduction wave was consumed in acidic and alkaline solutions corresponding to the reduction of the more easily N = N center. A second more cathodic irreversible , pH – dependent, 2-electron wave represents the reduction of quinolone ring. Cyclic voltammetry and convolution transforms were used to determine the kinetic parameters of the electroactive species.The extracted electrochemical parameters were confirmed via digital simulation.Controlled potential coulometry technique was used for calculation the overall number of electrons involved in electrode reaction.

Recent Applications of Mercury Electrodes for Monitoring of Pesticides: A Critical Review

AbstractThis critical review deals with possibilities and limitations of mercury electrodes in the field of voltammetric and amperometric determination of submicromolar concentrations of various electrochemically reducible pesticides. Attention is mostly focused on the last 10 years to show that even now mercury based electrodes are unsurpassed sensors for this purpose.

The octyltrimethylamonium bromide adsorption at the electrode/NaClO4 solution interface

The behaviour of octyltrimethylammonium bromide electrosorption on the mercury electrode in 1 mol/L NaClO4 was determined by means of double layer differential capacity measurements. The adsorption constants were derived from surface pressure data as a function of electrode charge density and cationic surfactant bulk concentration. Adsorption of octyltrimethylammonium bromide was analyzed using constants obtained from Frumkin, corrected Flory-Huggins and virial isotherms. It was found that the repulsive interactions for electrode charges close to 0 were the weakest between the adsorbed cations C11H26N+. In these conditions the surface concentration of the studied surfactant was the greatest.

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.

From mercury to nanosensors: Past, present and the future perspective of electrochemistry in pharmaceutical and biomedical analysis

Polarography was the first developed automated method of voltage-controlled electrolysis with dropping mercury electrode (DME). Then, hanging mercury drop and static mercury drop electrodes were added as an alternative indicator electrode. In this way, polarography turned formally into voltammetry with mercury electrodes in the electroreduction way. Solid electrodes such as noble metal and carbon based electrodes can be used for the investigation of the compounds for both oxidation and reduction directions, which is called voltammetry. The voltammetric and polarographic techniques are more sensitive, reproducible, and easily used electroanalytical methods that can be alternative to more frequently used separation and spectrometric methods. Furthermore, in some cases there is a relationship between voltammetry and pharmaceutical samples, and the knowledge of the mechanism of their electrode reactions can give a useful clue in elucidation of the mechanism of their interaction with living cells. The voltammetric and polarographic analysis of drugs in pharmaceutical preparations are by far the most common use of electrochemistry for analytical pharmaceutical problems. Recent trends and challenges in the electrochemical methods for the detection of DNA hybridization and pathogens are available. Low cost, small sample requirement and possibility of miniaturization justifies their increasing development.

Electrocapillary measurements by drop-time technique: Comparison of calibration methods

This paper considers the drop-time technique in electrocapillary measurements and focuses on calibration methods required to convert the drop-time t of a mercury electrode into the value of the interfacial tension γ. The relationships between t and γ, described in the literature, are reviewed and six calibration methods identified. On the basis of high-precision drop-time electrocapillary measurements carried out in 0.1moll−1 KCl aqueous solution, with γ values known from the absolute measurement method, the performance of the calibration methods, expressed in terms of measurement bias and uncertainty, is evaluated and compared. Better performance is observed for the methods that involve a nonlinear model such as γ=αtβ fitted to calibration data, instead of a single-point linear calibration commonly used. The measurement uncertainty U⩽0.12mNm−1 evaluated with these advanced calibration approaches corresponds to the level of accuracy achieved with the classical capillary electrometer.

Glycine adsorption on a mercury electrode modified by neodymium

Ranges of neodymium reduction potentials in aqueous solutions of potassium chloride at pH = 2 and in solutions containing glycine were determined by differential pulse polarography. The glycine complex with neodymium is not formed in the range of the amino acid concentration 0.001–0.12 M. Glycine adsorption on a mercury electrode and on an electrode modified with neodymium was studied by the cyclic voltammetry method.

Inhibition corrosion of zinc in concentrated alkaline electrolyte by combination of organic and inorganic compounds

Background. Zinc is widely used in chemical current sources (CCS) with alkaline electrolytes. One of the promising ways of self-discharge reduction and the service life improvement of the CCS is the use of zinc corrosion inhibitors. However, nowadays there is only a small number of known compounds that inhibit the corrosion of zinc alkaline, and the mechanism of the protective action of poorly understood.Objective. The objective is to study the influence of nitrohen-, oksyhen- and sulfur-containing organic compounds and their combinations with inorganic matter on corrosion of zinc in concentrated alkaline electrolyte, identifying the mechanism of their protective effect.Methods. The research was carried out by mass-metrical, volum-metrical and electrochemical methods with sheet (brand U0) and powder zinc10 M in KOH and in the same solution with inhibiting additives. Adsorption studies were performed by method of electro-capillary curve removal on a mercury electrode. Mixture state of organic and inorganic compounds was studied by NMR spectroscopy. Zinc surface state was studied by Auger spectroscopy coupled with ion etching after corrosion tests.Results. Combinations of polyoxyethylenealkyl ethers (FC VIS-15, DS-10, OP-4) and benzotriazole with salts of calcium and magnesium show high protective properties during zinc corrosion in10 M KOH. Protection degree of zinc electrode if any exists reaches 75 %. Inhibitors inhibit the process of hydrogen evolution in alkaline electrolytes but they do not affect significantly on anodic dissolution of zinc.Conclusions. There is the improvement of protective effect of organic inhibitors if there is calcium and magnesium in alkaline solutions. The obtained results indicate the prospects of using studied corrosion inhibitors in chemical power sources with zinc anode and alkaline electrolyte.

Редокс-свойства биядерных рений-платиновых винилиденовых комплексов с фосфорсодержащими лигандами

The redox properties of new binuclear μ-vinylidene complexes Cp(CO)2RePt(μ-C = C2HPh)LL′ [L = СO, L′ = PPh3 (1); L = СO, L′ = P(OPr)3 (2); L = L′ = PPh3 (3); L = L′ = P(OPr)3 (4)] were studied by electrochemical methods at a platinum, a glassed carbon and a dropping mercury electrodes in acetonitrile solutions. It was established that one-electron oxidation of 3 and 4 results in a cleavage of the Re-Pt and Pt-C1 bonds affording vinylidene complex Cp(CO)2RePt = C = CHPh and [PtLL′] fragments. In contrast to complexes 3 and 4, one-electron oxidation of 1 and 2 is reversible, indicating the greater electrochemical stability of lasts relative to 3 and 4.

Switching central trinucleotide sequences of DNA heptamer regulates adsorption on mercury electrode

The article aims to present an electrochemical investigation of DNA heptamers d(GCNNNGC) with a different central trinucleotide sequence (NNN = GAA, AAA, CCC, and GGG, where A, C, and G is adenine, cytosine, and guanine, respectively). In phosphate-acetate buffer at pH 5.8 all heptamers were adsorbed on a hanging mercury electrode, and these adsorbed heptamers underwent reduction and oxidation. The voltammetric reduction peaks of A and C moiety and oxidation peaks of G moiety at different concentrations (0.25–10 µmol dm−3) were analyzed. It was found that the changes in the central trinucleotide sequence of the heptamers result in altered adsorption ability at a charged phase interface. An electron transfer process in an adsorptive state was evidenced by the elimination voltammetric procedure. For the evaluation of adsorption efficiency of the heptamers the Langmuir adsorption model was applied and the adsorption coefficient b was calculated.

Parametric signal fitting of highly asymmetric voltammograms by using the exponentially modified Gaussian (EMG) function

A new multivariate curve resolution method is proposed according to the parametric signal fitting (PSF) strategy for the analysis of overlapping and highly asymmetric voltammetric signals. The method is based on the fitting of the well-known exponentially modified Gaussian (EMG) function, which had been previously used for the resolution of coeluted chromatographic peaks. The main advantage of this function is that one of the adjustable parameters is just the area under the peak, which is a magnitude more reliable than the peak height in the case of electrochemical systems providing highly asymmetric voltammograms. After a preliminary test with simulated data, the proposed method has been successfully applied to the experimental system Cd(II)–cysteine in both mercury and carbon screen-printed electrodes.

Development and Validation of Chronopotentiometric Method for Imidacloprid Determination in Pesticide Formulations and River Water Samples.

A new electrochemical method for determination of imidacloprid using chronopotentiometry on thin film mercury and glassy carbon electrode was presented. The most important experimental parameters of chronopotentiometry were examined and optimized with respect to imidacloprid analytical signal. Imidacloprid provided well-defined reduction peak in Britton-Robinson buffer on thin film mercury electrode at −1.0 V (versus Ag/AgCl (KCl, 3.5 mol/L)) and on glassy carbon electrode at −1.2 V (versus Ag/AgCl (KCl, 3.5 mol/L)). The reduction time was linearly proportional to concentrations from 0.8 to 30.0 mg/L on thin film mercury electrode and from 7.0 to 70.0 mg/L on glassy carbon electrode. The detection limits were 0.17 mg/L and 0.93 mg/L for thin film mercury and glassy carbon electrode, respectively. The estimation of method precision as a function of repeatability and reproducibility showed relative standard deviations values lower than 3.73%. Recovery values from 97.3 to 98.1% confirmed the accuracy of the proposed method, while the constancy of the transition time with deliberated small changes in the experimental parameters indicated a very good robustness. A minor influence of possible interfering compounds proved good selectivity of the method. Developed method was applied for imidacloprid determination in commercial pesticide formulations and river water samples.

Electrochemical and Theoretical Studies of Some Aromatic Oxime Derivatives Carrying –C=O and –NH–R′ Groups in the α- Position

The electrochemical reduction behavior of a series of aromatic oxime derivatives was characterized by voltammetry on a mercury electrode. Oxime compounds have both carbonyl and amino groups next to the functional oxime group and carry different substituent groups on the benzene side ring. Square wave voltammetry and differential pulse voltammetry revealed a strong pH dependency of the reduction peak potential and currents, while cyclic voltammetry revealed an irreversible nature of the electrode reaction. Substituent effects on the reduction of substances were closely related to their molecular structures estimated by theoretical Hartree-Fock calculations. The structure-reduction potential and pKa-substituent relationships are discussed.

An electrochemical study on interaction of copper ions with three isomers, picolinic, nicotinic and isonicotinic acids at physiological pH

The electrochemical behaviors of copper ions complexed with picolinic, nicotinic and isonicotinic acids (2-, 3- and 4-pyridinecarboxylic acids) in Britton–Robinson buffer (pH 7.4) was studied by polarographic and voltammetric techniques on a mercury electrode. This study showed that the reduction of complexed copper ions in the presence of nicotinic acid (NA) was carried out in two one-electron steps [Cu(II)/Cu(I) and Cu(I)/Cu(0)] whereas this cathodic process in the presence of picolinic acid (PA) or isonicotinic acid (INA) occurred in one two-electron step [Cu(II)/Cu(0)]. The stability of the Cu(I) complex can be sourced from the positions of carboxylate substituents on these isomeric ligands, binding to the copper center.

Rapid Screening Method for Detecting Ethinyl Estradiol in Natural Water Employing Voltammetry

17α-Ethinyl estradiol (EE2), which is used worldwide in the treatment of some cancers and as a contraceptive, is often found in aquatic systems and is considered a pharmaceutically active compound (PhACs) in the environment. Current methods for the determination of this compound, such as chromatography, are expensive and lengthy and require large amounts of toxic organic solvents. In this work, a voltammetric procedure is developed and validated as a screening tool for detecting EE2 in water samples without prior extraction, clean-up, or derivatization steps. Application of the method we elaborate here to EE2 analysis is unprecedented. EE2 detection was carried out using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) with a hanging mercury drop electrode (HMDE) in pH 7.0 Britton-Robinson buffer. The electrochemical process of EE2 reduction was investigated by cyclic voltammetry at different scan rates. Electroreduction of the hormone on a mercury electrode exhibited a peak at −1.16 ± 0.02 V versus Ag/AgCl. The experimental parameters were as follows: −0.7 V accumulation potential, 150 s accumulation time, and 60 mV s−1 scan rate. The limit of detection was 0.49 μg L−1 for a preconcentration time of 150 s. Relative standard deviations were less than 13%. The method was applied to the detection of EE2 in water samples with recoveries ranging from 93.7 to 102.5%.

The Atomic scale structure of liquid metal-electrolyte interfaces.

Electrochemical interfaces between immiscible liquids have lately received renewed interest, both for gaining fundamental insight as well as for applications in nanomaterial synthesis. In this feature article we demonstrate that the atomic scale structure of these previously inaccessible interfaces nowadays can be explored by in situ synchrotron based X-ray scattering techniques. Exemplary studies of a prototypical electrochemical system - a liquid mercury electrode in pure NaCl solution - reveal that the liquid metal is terminated by a well-defined atomic layer. This layering decays on length scales of 0.5 nm into the Hg bulk and displays a potential and temperature dependent behaviour that can be explained by electrocapillary effects and contributions of the electronic charge distribution on the electrode. In similar studies of nanomaterial growth, performed for the electrochemical deposition of PbFBr, a complex nucleation and growth behaviour is found, involving a crystalline precursor layer prior to the 3D crystal growth. Operando X-ray scattering measurements provide detailed data on the processes of nanoscale film formation.

A simple and rapid electrochemical sensing method for metribuzin determination in tap and river water samples

This paper describes an electroanalytical method for the determination of metribuzin using a thin film mercury electrode by chronopotentiometry.