Sonoelectroanalytical detection of lead at a bare copper electrode

The sonochemically facilitated, mercury free detection of Pb²⁺ at a copper electrode has been investigated as a means of simplifying the quantification of this important analyte and to minimise the interference of copper ion. The procedure relies upon maximising the formation of Pb-Cu intermetallic compounds leading to the emergence of a single, easily quantifiable stripping signal. Linear responses to Pb²⁺ were obtained with a sensitivity comparable to that obtained at a bare glassy carbon electrode. Interference from Cu²⁺, Zn²⁺ and Cd²⁺ was assessed on the copper electrode with no appreciable change in the Pb²⁺ voltammetric profile observed. In contrast, bare glassy carbon showed a significant change in Pb²⁺ voltammetric profile as Cu²⁺ was added, due to the formation of intermetallic species.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

The determination of lead,copper and cadmium by anodic stripping voltammetry at a mercury thin-film electrode

The determination of lead, copper and cadmium by anodic stripping voltammetry at a wax-impregnated graphite electrode, pre-plated with mercury, has been investigated. Electrode preparation and cell design are discussed, and the effects of mercury loading and sample pH on electrode sensitivity are described. Detection limits and precision on aqueous samples are reported. Calibration graphs are linear for lead and cadmium, but non-linear for low concentrations of copper. The depression of peak current and shift of peak potential for copper in chloride media are described and an explanation is proposed. Precision and recovery of metal additions are reported for digested samples of whole blood.     

Amperometric detection of amino acids with a passivated copper electrode

The amperometric behaviour of a copper electrode towards amino acids is studied by means of a rotating disc electrode. A theoretical model describing the anodic background current in a buffer solution and the increase of the current caused by amino acids is checked experimentally. The influences of the amino acid concentration, the rotation speed of the electrode and the composition of the buffer solution are studied. It is proved that chemical dissolution of a passivating film on the electrode surface, which is enhanced by the complexation reaction between the amino acid and copper(II) ions, is the principle of the phenomena observed. The applicability to flow systems is demonstrated.     

The detection of nitrate using in-situ copper nanoparticle deposition at a boron doped diamond electrode.

Electrochemical deposition from a 0.1 M sodium sulphate solution, containing Cu2+ (adjusted to pH 3 with hydrochloric acid) produced a well defined copper nanoparticle deposit on the surface of a boron doped diamond electrode. Changing conditions such as potential (-0.8, -1.0 and -1.2 V), time (5, 2 and 0.5 s) and concentration of Cu2+ (500, 250 and 100 microM) was found to give copper nanoparticles of varying size and particle density. The electrocatalytic properties of the copper surface towards nitrate reduction were explored. An in-situ copper nanoparticle production method was developed for the detection of nitrate; this involves electrodeposition, followed by linear sweep voltammetry for the reduction of nitrate and then application of a stripping potential to renew the electrode surface. The linear sweep was discovered to have homogenised the size of the nanoparticles but their number density was still dependant on the initial conditions of deposition. Some particles were still present at the surface after the stripping potential had been applied but repetitions of the procedure showed these did not have an effect on subsequent deposits. Optimisation of the method lead to applying a deposition potential of -0.8 V, at a BDD electrode for 5 s in a 0.1 M sodium sulphate solution (pH 3) containing 100 microM Cu2+ followed by a linear sweep at 1 V/s; this yielded a limit of detection of 1.5 microM nitrate. The analytical applicability of the technique was evaluated for nitrate detection in a natural mineral water sample and was found to agree well with that stated by the manufacturer.     

Electrogenerated chemiluminescence at bare glassy carbon electrode in basic media

Electrogenerated chemiluminescence (ECL) with three peaks at bare glassy carbon electrode (GCE) was observed as potential scanning between 0 and 2.6 V vs. Ag/AgCl in basic media. The peak potentials were seated at ca. 1.36 V, 1.72 V and 2.34 V in the positive sweeping, denoted as from ECL-I to ECL-III, respectively. Mechanisms of such ECL phenomena were proposed. For ECL-I peaked at 1.36 V, it might attribute to the oxidation of surface functional groups that analogy to alcoholic hydroxyl connected to the skeleton of GCE (S–R–CH₂OH), and the following ECL-II at 1.72 V, to the further oxidation of their products (S–R–CHO) to carbonyl compound (S–R–COO⁻). While for ECL-III at a high positive potential ca. 2.34 V, it was supposed to be related to the formation of singlet O₂ and its further conversion to triplet state.     

Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine

A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with a detection limit of 4.0 × 10⁻⁷ M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10⁻⁵ M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry. The text was submitted by the authors in English.     

Low potential electropolymerization of thiophene at a copper oxide electrode

Conductive polythiophene (PT) film was electrochemically deposited onto a copper electrode covered with an oxide film from distilled BF₃–diethyl ether (BFEE) solution containing 15 mM thiophene, and the oxidation potential of thiophene was relatively low (1.0 V versus Ag|AgCl). The obtained film was homogenous and flexible, and could be easily cut into any shape as desired.     

Voltammetric determination of sorbite at a mechanically renewed copper electrode

Potentials and currents of D-sorbitol oxidation peaks as a function of polarization conditions for a copper electrode in situ renewed by mechanically cutting a 0.5-μm surface layer are studied by direct-current cyclic voltammetry. Oxidation peaks of sorbite emerge in cyclic voltammograms recorded in alkaline supporting electrolytes (0.05–0.10 M KOH and NaOH solutions) upon scanning the potential to the anodic region (E _p = 0.50–0.58 V) and in the reverse direction (E _p = 0.60–0.62 V). The shape and parameters of these peaks depend on the concentration of KOH, because of the different copper oxides involved in the oxidation of sorbite formed at the electrode surface. The regeneration of the electrode surface is the necessary condition for good reproducibility of the peak parameters. The signals obtained on the surface of the unrenewed electrodes are almost halved and less reproducible. The calibration graph of the current of the sorbite oxidation peak as a function of its concentration is linear in the range from 5 × 10⁻⁴ to 1 × 10⁻² M.     

Carbon nanofiber electrode array for the detection of lead

A nanoelectrode array of vertically aligned carbon nanofibers was evaluated for the detection of Pb^2 + by anodic stripping voltammetry. The achieved detection limit of 1.73 nM is well below the environmental guidelines. The approach provides a safer alternative to the mercury electrodes commonly used for the detection of heavy metals.     

Potentiometric detection in ion chromatography using a metallic copper indicator electrode

Summary A metallic copper electrode housed in a suitable flowcell is shown to be a sensitive and versatile potentiometric detector for ion chromatography. This electrode may be used for direct or indirect detection of many inorganic anions and cations and also for organic acids. In the direct detection mode, electrode response is based on either complexation of copper ions at the electrode surface by eluted species, or on oxidation and reduction reactions for eluted species which are strong oxidants or reductants. Direct detection is therefore applicable to such species as amino acids, organic acids, chloride, bromide, iodide, chlorate, bromate and iodate. Indirect detection is possible for anions which do not complex copper ions, provided a copper complexing ligand (such as phthalate) is used in the eluent; cations which complex this ligand are also detectable. Indirect detection may be used for species such as nitrite, nitrate, acetate, formate, succinate, benzoate, alkaline earth ions and transition metal ions. Electrode calibration relationships are discussed and sample separations are presented, together with some typical detection limits attainable in the direct and indirect detection modes.Presented in part at a National Symposium on Ion Chromatography, held at the University of New South Wales, Kensington, Australia, Nov. 21, 1984.     

Capillary electrophoresis with end-capillary potentiometric detection using a copper electrode.

Potentiometric end-capillary detection in capillary electrophoresis has the advantage of relatively easy miniaturisation without having to compromise the concentration sensitivity. Potentiometric end-capillary detection using a copper electrode is also attractive because of the sensitive detection of many inorganic and organic UV-transparent ions and the ability to work in both direct and indirect mode. In this work, detection of a number of common anions in a tartrate electrolyte at pH 3 was studied. The influence of the end-capillary detection geometry on the detection performance was investigated. An end-capillary detection cell allowing the separation capillary to be changed without the need to realign the detection electrode was constructed and fitted into a commercial CE apparatus. Under the optimal configuration, which was a 25 microm diameter copper electrode aligned coaxially with a 25 microm capillary and positioned at a distance of about 25 microm from the capillary end, excellent peak shapes were achieved and comparison with simultaneous on-capillary photometric detection showed no additional peak broadening. Good sensitivity was obtained, resulting in concentration limits of detection (LODs) in the low microM range and mass LODs in the low amol range. Examples of separations of inorganic and organic anions are presented and the analytical potential of the detection method is assessed.     

Sensitive capillary electrophoretic determination of mercury species with amperometric detection at a copper electrode after cation exchange preconcentration

A capillary electrophoretic method for the separation of four mercury species with amperometric detection was developed. Inorganic Hg2+, methyl-, ethyl-, and phenyl-mercury were complexed with L-cysteine and separated in a counterelectroosmotic mode in an electrolyte solution comprised of 20 mM sodium tetraborate at pH 9.5. Amperometric detection of separated species was achieved at passivated copper electrode under electrocatalytic oxidation conditions. The four mercury species were separated in less than 8 min with LODs ranging from 170 to 450 microg/L. Cation exchange preconcentration was used to decrease the LODs down to 1.7 microg/L.     

Electrochemical reactions at a copper electrode in copper-conducting solid electrolytes

Potentiostatic measurements are used to show that, depending on the overvoltage sign, either electrochemical deposition or dissolution of copper occurs at the Cu/Cu₄RbCl₃I₂ interface at overvoltages η > 8–10 mV. At η = 10–100 mV, the reaction rate is limited by the formation and expansion of dissolution centers at the copper surface during anodic polarization and crystallization centers, during cathodic polarization. At η > 120 mV, the reaction rate is limited by charge transfer; the exchange current density is 2.7 mA cm^?2 and the anodic transfer coefficient is ～0.45. Under anodic polarization, formation of electron holes in the electrolyte occurs in parallel with the copper anodic dissolution. Therefore, nonstoichiometry of the electrolyte emerges in the near-electrode layer and divalent copper accumulates there.     

Effect of silver ions on codischarge of copper and silver at a platinum electrode at the copper underpotentials

Codischarge of copper and silver ions at potentials more positive than the equilibrium potential of the Cu⁺²/Cu system is studied by the voltammetry technique. At the Ag⁺ concentrationc below 10^-7 M, silver ions make no noticeable impact on the formation of a Cu_ad monolayer but decelerate that of supermonolayers of Cu at almost equilibrium potentials. Atc ≥ 4 × 10^-5 M, voltammograms indicate the concurrent adsorption of Cu_ad and Ag_ad and the nucleation and deposition of phase Ag     

Determination of uranium by adsorptive stripping voltammetry at a lead film electrode

An adsorptive stripping voltammetric procedure for the determination of U(VI) at an in situ plated lead film electrode is described. The U(VI) complex with cupferron was accumulated from an acetate buffer solution of pH 4.2 at the potential −0.65 V. The measurements were carried out from undeaerated solutions. The calibration graph for an accumulation time of 180 s was linear from 5 × 10⁻¹⁰ to 2 × 10⁻⁸ mol L⁻¹. The detection limit was 2 × 10⁻¹⁰ mol L⁻¹, the relative standard deviation for 2 × 10⁻⁸ mol L⁻¹ U(VI) was 4.3%. The proposed procedure was validated in the course of U(VI) determination in water certified reference materials.     

Anodic stripping voltammetry at a mercury film electrode: baseline concentrations of cadmium,lead, and copper in selected natural waters

A simple, rapid, and inexpensive anodic stripping voltammetric method with a mercury thin film electrode is reported for the establishment of baseline concentrations of cadmium, lead, and copper in natural waters. The procedure for routine surface preparation of wax-impregnated graphite mercury film electrodes requires about 30 min. Concentrations in the 0.006–6 μg l^-1 range are determined by linear d.c. voltage sweeps; the total time for a plating and stripping cycle is 6 min or less. The need for pressure-digesting samples for copper determinations is demonstrated. The a.s.v. results correlate well with corresponding analyses performed by graphite-furnace atomic absorption spectrometry.     

An adsorptive stripping voltammetry of nickel and cobalt at a solid lead electrode

For the first time, a solid lead electrode (PbE) was exploited for adsorptive stripping voltammetric determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent. The calibration graphs for Ni(II) and Co(II) were linear from 0.059 to 0.59 µg L^?1 and from 0.029 to 0.29 µg L^?1 (accumulation time 120 s), respectively. The analytical parameters such as the detection limit and separation of analytical signals obtained at the solid lead electrode were comparable with those obtained using a lead film electrode while better in comparison to those reported before for the bismuth film or solid bismuth electrodes. Co(II) could be determined in the presence of a large excess of Ni(II) and Zn(II). The proposed electrode was applied to determine Co(II) and Ni(II) traces in certified reference material and a natural water sample with satisfactory results.     

Sheath-flow electrochemical detection of amino acids with a copper wire electrode in capillary electrophoresis

Here, we report the detection of native amino acids using a sheath-flow electrochemical detector with a working electrode made of copper wire. A separation capillary that was inserted into a platinum tube in the detector acted as a grounded electrode for electrophoresis and as a flow channel for sheath liquid. Sheath liquid flowed outside the capillary to support the transport of the separated analytes to the working electrode for electrochemical detection. The copper wire electrode was aligned at the outlet of the capillary in a wall-jet configuration. Amino acids injected into the capillary were separated following elution from the end of the capillary and detection by the copper electrode. Three kinds of copper electrodes with different diameters-50, 125, and 300 μm-were examined to investigate the effect of the electrode diameter on sensitivity. The peak widths of the analytes were independent of the diameter of the working electrode, while the 300-μm electrode led to a decrease in the signal-to-noise ratio compared with the 50- and 125-μm electrodes, which showed no significant difference. The flow rate of the sheath liquid was also varied to optimize the detection conditions. The limits of detection for amino acids ranged from 4.4 to 27 μM under optimal conditions.