Hanging Drop Electrode Research Articles

A miniaturized atmospheric pressure glow microdischarge system generated in contact with a hanging drop electrode – a new approach to spectrochemical analysis of liquid microsamples

A newly developed atmospheric pressure glow discharge (APGD) microplasma system generated in contact with a hanging drop electrode (HDE) was investigated here in detail.

Amalgam Electrode-Based Electrochemical Detector for On-Site Direct Determination of Cadmium(II) and Lead(II) from Soils

Toxic metal contamination of the environment is a global issue. In this paper, we present a low-cost and rapid production of amalgam electrodes used for determination of Cd(II) and Pb(II) in environmental samples (soils and wastewaters) by on-site analysis using difference pulse voltammetry. Changes in the electrochemical signals were recorded with a miniaturized potentiostat (width: 80 mm, depth: 54 mm, height: 23 mm) and a portable computer. The limit of detection (LOD) was calculated for the geometric surface of the working electrode 15 mm2 that can be varied as required for analysis. The LODs were 80 ng·mL−1 for Cd(II) and 50 ng·mL−1 for Pb(II), relative standard deviation, RSD ≤ 8% (n = 3). The area of interest (Dolni Rozinka, Czech Republic) was selected because there is a deposit of uranium ore and extreme anthropogenic activity. Environmental samples were taken directly on-site and immediately analysed. Duration of a single analysis was approximately two minutes. The average concentrations of Cd(II) and Pb(II) in this area were below the global average. The obtained values were verified (correlated) by standard electrochemical methods based on hanging drop electrodes and were in good agreement. The advantages of this method are its cost and time effectivity (approximately two minutes per one sample) with direct analysis of turbid samples (soil leach) in a 2 M HNO3 environment. This type of sample cannot be analyzed using the classical analytical methods without pretreatment.

Influence of Environment on the Measurement of Rates of Charge Transport across AgTS/SAM//Ga2O3/EGaIn Junctions

This paper investigates the influence of the atmosphere used in the fabrication of top electrodes from the liquid eutectic of gallium and indium (EGaIn) (the so-called “EGaIn” electrodes), and in measurements of current density, J(V) (A/cm2), across self-assembled monolayers (SAMs) incorporated into Ag/SR//Ga2O3/EGaIn junctions, on values of J(V) obtained using these electrodes. A gas-tight measurement chamber was used to control the atmosphere in which the electrodes were formed, and also to control the environment in which the electrodes were used to measure current densities across SAM-based junctions. Seven different atmospheres—air, oxygen, nitrogen, argon, and ammonia, as well as air containing vapors of acetic acid or water—were surveyed using both “rough” conical-tip electrodes, and “smooth” hanging-drop electrodes. (The manipulation of the oxide film during the creation of the conical-tip electrodes leads to substantial, micrometer-scale roughness on the surface of the electrode, the extrusion of...

Speciation of Zinc Mixed Ligand Complexes in Salt Water Systems

Amalgam voltammetric method has been used to study heavy metal interaction in model lake water in KNO3 at 23¼C at concentration levels of genuine lake water of total ionic strength 1.44 M. Hanging drop amalgam electrode was prepared in situ before exchanging the medium containing Zn2+ ions for the sample solution with ligands of known concentrations. Half-wave potentials at the actual metal ion concentration in the lake and at a much lower one (10-2 times) were experimentally determined. Shifts in half-wave potentials are used to compute metal complex formation constants. The study reveals the existence of various species and a prediction is made of the distribution of the major labile complex species of Zn2+ present in the lake water. The concentration level of Zn2+ ions in the lake seems to play a role in determining the number of complexes formed and their stabilities. The results show that hydroxo/chloro and hydroxo/fluoro mixed ligand complexes have free Zn2+ ions as predominant species at the natural pH of the lake water and these systems are, therefore, potentially polluting. However, the contribution of OH- ions to the speciation of Zn is of no consequential effect because in its normal state, the [OH-] of the lake water is quite low and the aquatic life is, therefore, not threatened. The CO3 2- ions are the major contributors to the speciation of zinc in the lake water because the natural [CO3 2-] of 0.5 M is high. The normal lake water is thus, dominated by the carbonato complexes [ZnCO3Cl4]4-, [ZnCO3Cl2]2-, [ZnCO3Cl]- and to a less extent, ZnCO3. Keywords : Heavy metals, hanging drop electrode, amalgam voltammetry, speciation. Discovery and Innovation Vol. 19 (3) 2007: pp. 188-194

<b>Speciation of cadmium mixed ligand complexes in salt water lakes</b>

Amalgam voltammetry has been used to study heavy metal interaction in model lake water in KNO3 at 23 oC at concentration levels of genuine lake water. The hanging drop amalgam electrode was prepared in situ before exchanging the medium for the sample solution. Half-wave potentials at two metal ion concentrations were measured, one at the actual concentration in the lake while the other at a much lower one. The experimentally determined shifts in half-wave potentials are used to compute several formation constants. At the natural [CO32-] of 0.5 M in the lake, the main contributor to the speciation of cadmium is [Cd(CO3Cl2)]2-. At high [Cd2+], the DPASV detects the presence of free Cd2+ ions, hence, potential polluting effect, while the amalgam reports [Cd(CO3)2Cl)]3- to be dominant above [CO32-] = 0.8 M. There is a variation in the number of complexes detected, their stabilities and percentage distribution in the two methods. Cd2+ ion concentration also affects the number of complexes formed and their stabilities. KEY WORDS: Heavy metals, Hanging drop electrode, Amalgam voltammetry, Speciation, Cadmium mixed ligand complexes Bull. Chem. Soc. Ethiop. 2003, 17(1), 85-94.

The mechanism of the electrochemical reaction of lysozyme at the mercury electrode

Abstract The mechanism of the electrochemical reaction of lysozyme (Ly(SS)4) at the mercury hanging drop electrode (HMDE) was investigated in Na2HPO4 + citric acid (pH 5). A pair of broader cathodic and anodic peaks appears at the same potential. The peak potential is −0.47 V vs. SCE. When a fresh mercury drop of the HMDE is pre-equilibrated with the stirred solution for a certain time at a potential about 0 V vs. SCE, only a sharp narrow cathodic peak is observed at the same potential as the peak without the pre-equilibrium and there is no peak corresponding to its anodic process. In the two eases, the mechanism of the electrochemical reaction is different. The reaction scheme without the pre-equilibrium between the mercury electrode and the solution containing lysozyme can be written as follows: Ly(SS)4(soln) ⇌ Ly(SS)4(ads); Ly(SS)4(ads) + 2H+ + 2e− ⇌ Ly(SS)2(ads). In the case with the pre-equilibrium the reaction mechanism may be: Ly(SS)4(soln) ⇌ Ly(SS)4(ads); Ly(SS)4(ads) + Hg ⇌ Ly(SS)3(SS2−)Hg2+ (ads);Ly(SS)3(SS2−)Hg2+ (ads) + 2H+ + 2e− → Ly(SS)3(SH)2(ads) + Hg; Ly(SS)3(SH)2(ads) 1− 2H+ − 2e− ⇌ Ly(SS)4(ads). The two kinds of reaction proceed on the disulfide bond at the position of 6–127, because it is at the edge of the dimensional structure of the molecule of lysozyme.

Trace Analysis of Iron in Environmental Water and Snow Samples from Poland

Abstract A voltammetric method for the determination of iron at detection limit of 4 μg/l is described, using the catalytic current of the reduction of the Fe(III)-triethanolamine (TEA) complex in the presence of bromate ions. the determination was performed at a mercury hanging drop electrode without preconcentration, using the TEA alkaline solution as a supporting electrolyte and the differential pulse technique. A peak current for the Fe(III)-TEA catalytic reduction was observed at a potential of-1.0 V (Ag/AgCl saturated electrode). the influence of TEA, BrO3 and NaOH concentrations on the peak height was studied. It was found that a 100-fold excess of Mn, a 50-fold excess of Cr(VI) and Zn did not interfere in the determination. This method was applied to the determination of iron in water, snow and waste water samples.

Determination of hydrazine in polyvinylpyrrolidone by derivatization and square wave voltammetry

A rapid and precise method has been developed for the determination of hydrazine in polyvinylpyrrolidone (PVP). Hydrazine is converted to salicylaldazine by reaction with salicylaldehyde. After extraction, the azine is reduced at −1.56 V versus the SCE at the hanging drop electrode. Detection is accomplished using square wave voltammetry and comparison to an external salicylaldazine standard. The described procedure can detect as little as 70 ng/g hydrazine in PVP.

ChemInform Abstract: Electrochemical Kinetics of Bismuth Sulfide Formation on Bismuth Amalgam.

AbstractOn a hanging drop electrode of bismuth amalgam in aqueous NaHCO3 solution containing HS‐, a monolayer of bismuth sulfide is formed having a charge densitiy of 430 μC cm‐2 (potential sweep experiments), which is in close agreement with the value predicted from the (010) plane of orthorhombic bismuth sulfide, with chains of (Bi4S6)n on the electrode surface.

Electrochemical kinetics of bismuth sulphide formation on bismuth amalgam

A monolayer of bismuth sulphide was formed anodically on a hanging drop electrode of bismuth amalgam in aqueous NaHCO 3 solution containing HS − at 20°C. Potential sweep experiments showed a monolayer current peak with a charge density of 430 μC cm −2, in close agreement with the value predicted from the (010) plane of orthorhombic bismuth sulphide, with chains of (Bi 4S 6) n on the electrode surface. The monolayer peaks of HgS were suppressed by prior formation of the Bi 2S 3 monolayer, and a mixed film of Bi 2S 3 and Bi 2O 3 formed at a higher overpotential. Galvanostatic transients gave a small nucleation peak, followed by growth at a constant overpotential until the monolayer was complete. Potentiostatic transients showed an asymmetric current peak indicating that the mechanism of monolayer formation involves instantaneous nucleation followed by expansion and overlap of two-dimensional centres.

The long lasting sessile drop mercury electrode—a new approach to measurements at high negative potentials

The performance of the long lasting sessile drop mercury electrode ( llsdme) as a working electrode for various electrochemical techniques was studied. Dimethylpyrrolydinium [ E 1 2 ≈ −2.7 V ( sce)] and 2,4,6-trimethylpyridine [ E 1 2 ≈ −2.85 V ( sce)] were used as substrates in DMF as the solvent and tetrabutylammonium fluoroborate as the electrolyte. Measurements obtained with various working electrodes were compared and the llsdme was found to be more reliable than the dropping mercury or hanging drop electrodes.

The partition of amines between water and an organic solvent phase

The partition of a series of protonated amines (aniline, benzylamine, 2-phenylethylamine and related compounds) between water and nitrobenzene was investigated using electrochemical approaches (cyclic voltammetry and differential pulse stripping voltammetry) which made it possible to infer the transport and thermodynamic parameters of the partition process. Micromolar concentrations of the protonated amines in the aqueous phase can be determined by DPSV at the electrolyte hanging drop electrode. The function of an amine as the proton acceptor in the facilitated proton transfer across the water/organic solvent phase was discussed.

The partition of amines between water and an organic solvent phase

The partition of a series of protonated amines (aniline, benzylamine, 2-phenylethylamine and related compounds) between water and nitrobenzene was investigated using electrochemical approaches (cyclic voltammetry and differential pulse stripping voltammetry) which made it possible to infer the transport and thermodynamic parameters of the partition process. Micromolar concentrations of the protonated amines in the aqueous phase can be determined by DPSV at the electrolyte hanging drop electrode. The function of an amine as the proton acceptor in the facilitated proton transfer across the water/organic solvent phase was discussed.

The direct and indirect determination of traces of copper, lead and cadmium in mercury by voltammetry at the hanging mercury drop electrode

Direct and indirect method of determining traces of copper, lead and cadmium in mercury are proposed. In the direct method, a small portion of the mercury under test is introduced into the hanging drop electrode, the anodic voltammogram is recorded, and the concentration of the contaminants in the mercury phase are determined from the heights of the anodic peaks. The detection limits for this method are 2 × 10 −7 mol dm −3 for lead and cadmium and 4 × 10 −7 mol dm −3 for copper. The use of the pulse technique gives a fivefold improvement in the detection limits for lead and cadmium. In the indirect method, the contaminating metals are oxidized from mercury to an appropriate supporting electrolyte, and the determination is completed in the same electrolytic cell by anodic stripping voltammetry at a hanging mercury drop electrode. The detection limits for this procedure are 1 × 10 −8 and 2 × 10 −9 mol dm −3 for the voltammetric and differential pulse techniques respectively; the time required is 30–40 min.

Reactions of bases of nucleic acids with mercury electrode. anodic pulse-polarographic currents of pyrimidine bases and their derivatives

Anodic currents of pyrimidine bases were studied by using differential and normal pulse polarography, cyclic voltammetry, and classical polarography in alkaline medium. All pyrimidine bases occurring usually in nucleic acids (cytosine, uracil, thymine, 5-methylcytosine, and hydroxymethylcytosine) gave anodic DPP peaks, NPP and d.c. polarographic waves at potentials close to 0 V due to the formation of sparingly soluble salts with mercury. Nucleosides and nucleotides derived from cytosine, uracil, and thymine were inactive. The mentioned bases and other pyrimidine derivatives (isocytosine, uracil-5-carboxylic acid, uracil-6-carboxylic acid (orotic acid), 2-amino-4,6-dioxypyrimidine, 2-amino-4,6-dioxy-5-methylpyrimidine, 4-amino-2,6-dioxy-pyrimidine, and 5-amino-2,4-dioxypyrimidine) gave anodic peaks and cathodic stripping peaks during reversal of the potential sweep on a hanging drop electrode, whereas 2-aminopyrimidine and 2-hydroxypyrimidine were inactive; the concentrations used were 5 . 10-6 - 5 . 10-5M. The bahaviour of cytosine, uracil, and thymine in DPP and NPP was studied at various concentrations of the bases, pH values, pulse amplitudes, etc. Differences between the behaviour of uracil and thymine were large at higher concentrations at which the electrode surface was fully covered, and they were explained on the assumption of a different adsorption behaviour of these compounds and a large tendency of uracil to form a film on the electrode.

The contribution of electrochemical reactions to sulfur transfer from electrode to slag in electroslag remelting

In order to assess the contribution of electrochemical reactions to refining reactions, such as sulfur removal, in electroslag remelting, electrochemical experiments which simulate conditions at the electrode/slag, and liquid metal pool/slag interfaces have been carried out. Liquid copper electrodes and a CaO-Al2O3-CaF2 electrolyte were used. The experimental technique involved chronopotentiometry at constant current. Sulfur reversion from slag to metal is shown to be a diffusion controlled, reversible electrochemical process involving two electrons. On the other hand sulfur transfer from metal to slag occurs both by the diffusion controlled electrochemical reaction and the direct exchange reaction. A hanging drop electrode system was used to simulate conditions at the electrode/slag interface. Further experiments on the hanging drop electrode with and without applied current showed that direct reaction was a minor contribution to sulfur removal. The results are compared to findings from industrial practice.

A micro method for direct determination of ionic fluoride in body fluids with the hanging drop fluoride electrode

A simple method for direct determination of ionic fluoride in 5 μl samples of body fluids with the hanging drop fluoride electrode, using sodium acetate buffer (pH 4.8) is described. The hanging drop electrode should prove useful in experimental investigations employing small laboratory animals and in clinical laboratories.

Specific influence of electrolysis potential on the Zn-peak in chronovoltamperometry on the HMDE

Summaryo1.Adsorption on the Hg hanging drop electrode, established during the preliminary electrolysis, influences the Ep and σ of the anodic peak during the subsequent stripping process.2.In the particular case of zinc ions in alkaline solutions, at a low electrolysis potential (Eel), Zn(OH)2 is formed as an intermediate and is adsorbed at the electrode interface. At higher potentials this layer disappears. These potentials are ca. — 1.92 V (SCE) in 0.1–1 N KOH or — 1.82 V (SCE) in 1.5–3 N KOH. The influence of this layer in the stripping process is similar to that of other adsorbed layers, e.g. of gelatine.3.The effect described is of importance in the selection of optimum conditions in the technique of anodic stripping voltammetry.4.Although observed in the case of zinc ions, the effect described may also occur in other systems. Therefore a study of the influence of Eel on Ep and σ is always advisable and should not be limited to the influence on h. Adsorption on the Hg hanging drop electrode, established during the preliminary electrolysis, influences the Ep and σ of the anodic peak during the subsequent stripping process. In the particular case of zinc ions in alkaline solutions, at a low electrolysis potential (Eel), Zn(OH)2 is formed as an intermediate and is adsorbed at the electrode interface. At higher potentials this layer disappears. These potentials are ca. — 1.92 V (SCE) in 0.1–1 N KOH or — 1.82 V (SCE) in 1.5–3 N KOH. The influence of this layer in the stripping process is similar to that of other adsorbed layers, e.g. of gelatine. The effect described is of importance in the selection of optimum conditions in the technique of anodic stripping voltammetry. Although observed in the case of zinc ions, the effect described may also occur in other systems. Therefore a study of the influence of Eel on Ep and σ is always advisable and should not be limited to the influence on h.

Specific influence of electrolysis potential on the Zn-peak in chronovoltamperometry on the HMDE

Summary o 1. Adsorption on the Hg hanging drop electrode, established during the preliminary electrolysis, influences the Ep and σ of the anodic peak during the subsequent stripping process. 2. In the particular case of zinc ions in alkaline solutions, at a low electrolysis potential (Eel), Zn(OH)2 is formed as an intermediate and is adsorbed at the electrode interface. At higher potentials this layer disappears. These potentials are ca. — 1.92 V (SCE) in 0.1–1 N KOH or — 1.82 V (SCE) in 1.5–3 N KOH. The influence of this layer in the stripping process is similar to that of other adsorbed layers, e.g. of gelatine. 3. The effect described is of importance in the selection of optimum conditions in the technique of anodic stripping voltammetry. 4. Although observed in the case of zinc ions, the effect described may also occur in other systems. Therefore a study of the influence of Eel on Ep and σ is always advisable and should not be limited to the influence on h.

Adsorption of camphor, camphene, pinene, naphthalene and nonylic acid at the mercury-solution interface

The equilibrium capacitance of the interface between mercury and solutions containing camphor has been measured as a function of potential with a hanging drop electrode by using a low frequency (45 Hz) a.c. bridge. The data show that the capacitance in the region of adsorption is always that of a monolayer of adsorbed camphor, independent of its bulk concentration. The capacitance-potential curve for the solution saturated with camphor shows the usual desorption peaks if equilibrium measurements are made at millivolt intervals near the critical potentials of desorption. From a theoretical analysis of the capacitance data, the molecular area on adsorption as well as the adsorption potential for camphor have been calculated. It is shown that camphene and α-pinene are adsorbed like camphor at the mercurysolution interface with phase transition, whereas naphthalene is adsorbed without any phase transition. The capacitance curve for nonylic acid adsorption at the mercury-solution interface is not characterised by any hysteresis if measurements are made at equilibrium on an initially clean surface. A bridged carbon atom in a surfactant, as also a long hydrocarbon chain, seem to give condensed monolayers on adsorption.