Surface Of Mercury Drop Electrode Research Articles

Electrochemical characterization of Cobalt(II)-Complexes involved in marine biogeochemical processes. I. Co(II)-4-nitrocatechol and Co(II)-Humate

Cobalt (II) as an important micronutrient for numerous biological processes in marine environment, has been tested in model aqueous solutions with naturally occurring ligands 4-nitrocatecol (4NC) and humic acid (HA) by voltammetry and spectrophotometry. Irreversible, two-electron reduction processes of Co(II)–4NC and Co(II)-HA complexes adsorbed on the mercury drop surface, depending on accumulation time and composition of the solution (cCo, c4NC,cHA and pH), were detected. Complexes Co:L = 1:1 stability constants formed only in the solution, were determined by spectrophotometry and amout to log KCo(II)4NC = 3.98 (pH = 8.2) and log KCo(II)4NC = 5.76 (pH = 6.5), and log KCo(II)HA = 3.80 (pH = 8.2). Co:L = 1:2 complexes Co(II)-(4NC)2 at pH 6.5 and 8.2 and Co(II)-(HA)2 at pH 8.2, formed at the mercury drop electrode surface as hydrophobic specia, were detected only by voltammetric measurements. Conditional stability constants were calculated by the CLE/ACSV method: log KCo(II) (4NC)2 = 21.86 (pH = 8.2), log KCo(II) (4NC)2 = 21.11 (pH = 6.5) and log KCo(II) (HA)2 = 11.32 (pH = 8.2).

Adsorption of cationic surfactants on covered hanging mercury drop electrode surface of variable area

Cetyldimethylbenzylammonium chloride (CDBACl) or cetyltrimethylammonium bromide (CTAB) is preadsorbed on mercury and used as substrate. The adsorptive stripping voltammetry with the two-step procedure is used. The mercury droplet with the preadsorbed surfactant is expanded in aqueous solutions of KCl, KBr, CTAB, CDBACl, or cetylethyldimethylammonium bromide (CEDAB). The surface area was increased from 0.0022cm2 up to 0.0571cm2. The surfactant molecules are maintained close to each other and in the vicinity of the electrode by the applied electric field. The expanding of the droplets resulted in a reorientation of the adsorbed molecules depending on the surfactant surface concentration. In some cases, condensed films were observed. Differences were noticed in the adsorption and desorption potential region. A linear increase in the capacitance current with the surface area was found in all cases up to a maximum increase in the surface area. Partly disorganized films were also observed. In some cases, defects were noticed during expansion. In one case, fractal structure was observed.

Electrochemical interfacial adsorption mechanism of polyphenolic molecules onto Hanging Mercury Drop Electrode surface (HMDE)

The electrochemical interfacial adsorption of a series of polyphenolic molecules (i.e. polyhydroxybenzoic acids) at the Hanging Mercury Drop Electrode (HMDE)–electrolyte interfaces were investigated using Square Wave-Adsorption Cathodic Stripping Voltammetry (SW-AdCSV) at pH 7.5. Polyhydroxybenzoic acids bearing one 4-hydroxybenzoic acid, two 3,4-dihydroxybenzoic acid (protocatechuic) or three 3,4,5-trihydroxybenzoic acid (gallic) OH-groups at positions C3, C4 and C5 on the benzene ring were studied. The complex interfacial electrochemical behaviour of these molecules has been deconvoluted to (i) adsorption evens and (ii) redox formations at the HMDE interface. The approach presented is based on the comparative analysis of the SW-AdCSV signals in conjunction with the molecular structure of the molecules. Accordingly, theoretical calculations, involving nonlinear-fit, resulted in the identification of the interfacial reaction mechanism of adsorbed gallic acid on the HMDE.

Preconcentration of the lipid-lowering drug lovastatin at a hanging mercury drop electrode surface

Adsorption and reduction of lovastatin were investigated by cyclic and square-wave voltammetry on a hanging mercury drop electrode in aqueous solutions over a wide pH range (4–9). The electroreduction of lovastatin proceeds via a surface EC mechanism in the whole pH range investigated. Using adsorptive stripping voltammetry, the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 6 at −1.49 V which can be used to determine trace amount of lovastatin. The linear concentration range of application was 1.0 × 10−8–1.0 × 10−7 M by using an accumulation potential of −0.5 V and a 90 s pre-concentration time. The method has been successfully applied for the determination of lovastatin in a spiked human serum sample.

Electrochemical Renewal of Stationary Mercury Drop or Meniscus Electrodes

AbstractWe show that a liquid mercury drop electrode surface can be electrochemically renewed without mechanical detachment of the drop. Voltammetric experiments with a mechanically renewed stationary (hanging) mercury drop or meniscus electrode (SME) and an electrochemically renewed SME are compared. The measurements were performed with two surface active organic depolarizers, i.e., 2‐aminoanthraquinone and dithiothreitol and surface inactive Cd(NO3)2. The results show that efficient purely electrochemical renewal of the electrode surface of SME for voltammetric purposes is possible.

Simultaneous determination of Pt and Rh by catalytic adsorptive stripping voltammetry, using hexamethylene tetramine (HMTA) as complexing agent

Characteristics of the adsorption/electro-reduction of Pt/Rh hexamethylene tetramine (HMTA) complex on static mercury drop electrode surface were studied. Cyclic voltammetry was carried out to get the insight about the mechanistic behaviour of the catalytic current obtained in the voltammetric scan of Pt/Rh HMTA complex in acidic solution. Adsorptive stripping voltammetry using HMTA as the complexing agent was found to be highly sensitive method for the determination of Pt/Rh. Voltammetric measurements were carried out using hanging mercury drop electrode (HMDE) as the working electrode, a glassy carbon rod as the counter and an Ag/AgCl/KCl saturated as the reference electrode. Various electrochemical parameters like deposition potential, deposition time, concentration of the ligand, supporting electrolyte etc. were optimized. The detection limit of Pt and Rh was found to be 4.38 pML −1 and 2.80 pML −1, respectively for the deposition time of 30 s. Simultaneous determination of Pt(II) and Rh(III) in water samples was possible. The method was found to be free from the commonly occurring interfering ions such as Cu(II), Cd(II), Zn(II), Pb(II), Cr(III), Cr(VI), Fe(III), Fe(II), Ni(II) and Co(II). Spike recovery tests for both Pt and Rh in tap water and sea water samples were also carried out. The method has been verified by analyzing certified reference material (WMG-1).

Mathematical Modelling of the Electrode Process of Azithromycin Using Cyclic Voltammetry at Hanging Mercury Drop Electrode

A theoretical treatment is presented to predict the kinetic behaviour of azithromycin at the surface of hanging mercury drop electrode using cyclic voltammetry. A model is developed to incorporate the occurrence of adsorption of the oxidized and reduced species of azithromycin at the surface of mercury drop electrode. An analytical solution was obtained using MATHEMATICA (V-3, Wolfram Research, Inc.) to predict the cyclic voltammetric profiles by calculating the currents resulting after applying variable potentials ranging –1.9 to –1.3 V versus Ag/AgCl. Simulation runs at different initial concentrations of azithromycin and different scan rates showed good agreement with experimental findings. However, this model should be modified to describe a multilayer adsorption with irreversible electrochemical reaction.

Differential-pulse voltammetric determination of low μg l−1 cyanide levels using EDTA, Cu(II) and a hanging mercury drop electrode

The proposed method for cyanide determination at the ultratrace level by differential pulse voltammetry is based in the sensitivity enhancement obtained when both Cu(II) and EDTA are present in the background electrolyte. Comparison of the detection limits and linear dynamic ranges using the conventional borate (pH 9.75), and the proposed borate-EDTA–Cu(II) background electrolytes was carried out. Best results have been obtained with the addition of 0.5mmoll−1 EDTA and 0.02mmoll−1 of Cu(II), which allow a detection limit of 1.7μgl−1 CN− (65nmoll−1 — absolute detection limit 34ng) with a precision better than ±2% for a 40μgl−1 level. Calibration range extended from detection limit up to 100μgl−1. Cyclic voltammetry indicates that the measured cyanide peak is obtained when the electrogenerated CuCN adsorbed onto the hanging mercury drop electrode surface, is oxidised at positive going potential scan. The method has been successfully applied to various industrial waste waters such as metal-finishing waste waters, water/sand mixtures from cleaning processes of coke production, leachates from wastes obtained from electrolytic cells of aluminium production, and liquors from gold extraction industry. Results obtained by the proposed method showed good agreement with those obtained by the standard methods (ion-selective potentiometry and the spectrophotometric pyridine method).

Voltammetry of compounds confined at the hanging mercury drop electrode surface

With the introduction of PC-driven analytical voltammetric instrumentation, the investigation of several useful voltammetric characteristics of electroactive compounds has become much easier, increasing the possibilities of discrimination in analysis. In this work some suggestions are given for the development of strategies to apply in the systematic study of compounds adsorbed on a hanging mercury drop electrode (HMDE). This would establish their behaviour under different experimental conditions for analytical purposes. Although indications of reactant adsorption can be easily detected with normal-pulse voltammetry (NPV), this technique is not as appropriate as square-wave voltammetry (SWV) for analytical purposes. The different effects of SW frequency and amplitude on signals obtained with two quinoxalines were studied. Based on their different electrochemical reversibilities (dimethylquinoxaline (DMQ) reversible, and hydroxyquinoxaline (HOQ) irreversible), these two compounds could be determined simultaneously, in spite of their similar peak potentials. A marked effect of the surfactant tetraphenylphosphonium chloride (TPPC) on the peak potential of the azo colouring matter, azorubine, was also observed. A noticeable increase in peak height occurs at relatively low frequencies, in contrast to the (expected) reduced peak height at high frequencies. Finally the possibility of avoiding the time consuming need to remove oxygen is also considered. At high SW frequencies the interference of oxygen is drastically reduced. DMQ at concentrations as low as 10 −7 M could be determined without oxygen removal by using a SW frequency higher than 100 Hz. A direct application was made to the voltammetric determination of diacetyl in brandy: this involved prior derivatization of the compound with o-phenylenediamine to form DMQ.

Square-wave voltammetry of copper–phenanthroline–tributylphosphate complex

The mechanism of synergetic adsorptive accumulation of copper(II)–phenanthroline–tributylphosphate (Cu–phen–TBP) complex at the mercury drop electrode surface has been described. The behaviour and characteristics of the CuII mixed ligand complex was studied and the relationship between the properties of square-wave response and the parameters of a charge transfer and of the excitation signal are discussed. Square-wave voltammetric response of the Cu-phen-TBP complex are analysed according to the theoretical results.

A square‐wave voltammetry in a cathodic stripping mode

AbstractA model of cathodic stripping square‐wave voltammetry (SWV) of insoluble mercuric salt accumulated at the mercury drop electrode surface is developed. Theoretical relationships between the properties of responses and the parameters of both the redox reaction and the SWV signal are analyzed. Both reversible and quasireversible redox reactions are considered. The nature of quasireversible maximum is discussed. Numerical simulations are compared qualitatively with the SW stripping voltammograms of electrodeposited HgS.

ChemInform Abstract: POLAROGRAPHY OF AMMONIUM 1‐PYRROLIDINECARBODITHIOATE AND AMMONIUM 2‐CARBOXY‐1‐PYRROLIDINECARBODITHIOATE AT THE DROPPING MERCURY ELECTRODE

Direct current and alternating current polarographic behaviors of ammonium 1-pyrrolidinecarbodithioate (APCD) and ammonium 2-carboxy-1-pyrrolidinecarbodithioate (ACPCD) were investigated at the dropping mercury electrode. APCD showed an adsorption pre-wave (−0.70 V vs. SCE) and one-electron oxidation wave (−0.42 V). ACPCD showed only an adsorption wave (−0.65 V). These results were also confirmed by the investigation of the electrocapillary curves and the current-time curves. The surface excess of APCD or ACPCD on the surface of mercury drop electrode at the potential which the adsorption process was observed were 5.76×10−10 mol/cm2 and 2.62×10−10 mol/cm2, respectively.

Polarography of Ammonium 1-Pyrrolidinecarbodithioate and Ammonium 2-Carboxy-1-pyrrolidinecarbodithioate at the Dropping Mercury Electrode

Abstract Direct current and alternating current polarographic behaviors of ammonium 1-pyrrolidinecarbodithioate (APCD) and ammonium 2-carboxy-1-pyrrolidinecarbodithioate (ACPCD) were investigated at the dropping mercury electrode. APCD showed an adsorption pre-wave (−0.70 V vs. SCE) and one-electron oxidation wave (−0.42 V). ACPCD showed only an adsorption wave (−0.65 V). These results were also confirmed by the investigation of the electrocapillary curves and the current-time curves. The surface excess of APCD or ACPCD on the surface of mercury drop electrode at the potential which the adsorption process was observed were 5.76×10−10 mol/cm2 and 2.62×10−10 mol/cm2, respectively.