Mercury Film Glassy Carbon Research Articles

Extraction Induced by Microemulsion Breaking and Square Wave Voltammetry: A Promising Union to Monitor Cd, Pb and Cu in Biodiesel

A new approach involving square wave anodic stripping voltammetry was developed to simultaneously determine cadmium and lead and, in the same cell, sequentially copper, in biodiesel after extraction induced by microemulsion breaking. The composition of the water-in-oil microemulsion involved 10.50 mL biodiesel, 4.20 mL n-propanol and 0.30 mL of the 6.0 mol L-1 HNO3 solution. The extraction was carried out by adding 1.10 mL ultrapure water resulting in two well separated phases: an upper organic phase, and a lower aqueous phase containing the analytes. The apparatus comprised a portable potentiostat and a cell with an in situ plated mercury film glassy carbon electrode as working electrode. The limits of detection for Cd, Pb and Cu were 0.33, 0.48 and 0.66 μg L-1, respectively. The accuracy of the method was evaluated by recovery assays of spiked samples and by analyzing a standard reference material.

Stripping voltammetry for field determination of traces of copper in soil extracts and natural waters

Field analysis is becoming increasingly popular, owing to the commercial availability of portable instruments, fast response and cost-effectiveness. Nevertheless, field analysis requires a careful planning.Voltammetry is particularly suitable for the field determination of trace elements thanks to its sensitivity, simplicity of operation and instrument portability. Therefore, in this work, Anodic Stripping Voltammetry (ASV) was applied to the field determination of Cu(II), as a pilot analyte, in natural water and in a soil extract, and the experiment organization was carefully detailed. Four solid electrodes were previously tested in the laboratory and their performances in terms of precision, linearity, trueness and overall ease of operation were discussed. The well-known Mercury Film Glassy Carbon Electrode (MF-GCE) was selected for field measurements because it yielded the most satisfactory performances. Anyway, the suggestions given in this paper can be useful for other electrodes and other analytes; in particular, a list of the items that should be brought to the site where analysis will be carried out was proposed in order to provide a general guide for the organization of field measurements by voltammetry.

Use of Mercury Film Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotubes in Electrochemical Analysis of DNA

AbstractMercury film plated on a glassy carbon electrode modified with multiwalled carbon nanotubes (MF/MWNTs/GCE) was used for the analysis of single (ss) and double stranded (ds) DNA, as well as for Jurkat genomic DNAs methylated to different degrees. The results indicated that the DNA molecules adsorbed quite strongly on the MF/MWNTs/GCE surface allowing ex situ adsorption and produce well developed peaks (due to cytosine and adenine) by using adsorptive stripping (Ads, ex situ) square wave voltammetry (SWV). Also, SWV of Jurkat DNA mixtures methylated to different degrees revealed a linear decrease of the peak height with increasing methylation indicating an increase of structural rigidity.

DNA Hybridization at Magnetic Nanoparticles with Electrochemical Stripping Detection

AbstractA simple and practical method for electrochemical DNA hybridization assay has been developed to take advantage of magnetic nanoparticles for ssDNA immobilization and zinc sulfide nanoparticle as oligonucleotide label. Magnetic nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then amino silane was coated onto the surface of magnetite nanoparticles. The magnetic nanoparticles have the advantages of easy preparation, easy surface modification and low cost. The target ssDNA with the phosphate group at the 5′ end was then covalently immobilized to the amino group of magnetite nanoparticles by forming a phosphoramidate bond in the presence of 1‐ethyl‐3‐(3‐dimeth‐ylaminopropyl)carbodiimide (EDAC). The zinc sulfide (ZnS) nanoparticle‐labeled oligonucleotides probe was used to identify the target ssDNA immobilized on the magnetic nanoparticles based on a specific hybridization reaction. The hybridization events were assessed by the dissolution of the zinc sulfide nanoparticles anchored on the hybrids and the indirect determination of the dissolved zinc ions by anodic stripping voltammetry (ASV) at a mercury film glassy carbon electrode (GCE). The proposed method couples the high sensitivity of anodic stripping analysis for zinc ions with effective magnetic separation for eliminating nonspecific adsorption effects and offers great promise for DNA hybridization analysis.

Stripping Chronopotentiometry with Dry‐Preservable Supporting Electrolyte

AbstractThe determination of some toxic metals by stripping chronopotentiometry with a supporting solution having an unconventional composition has been investigated with the aim of using such components in disposable measuring cells preservable in dry state and quite ready for use, only needing addition of a small volume of sample. The new supporting solution is prepared with a solid strong acid, p‐toluenesulfonic acid, in the place of the inorganic acids commonly used to improve the cation availability. The other components are, as usual, sodium chloride, which fixes the potential of the screen‐printed silver – silver chloride reference electrode, and mercury(II) chloride as the plating agent. This supporting solution has been tested in batch measurements with the mercury film glassy carbon electrode as well as with screen‐printed carbon‐ink electrodes, either with mercury film or bare. The physical shape of the mercury layer electrolytically deposited on screen‐printed carbon‐ink electrodes from a supporting solution containing 0.1 M p‐toluenesulfonic acid and 0.1 M sodium chloride has been investigated by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) microanalysis. In chronopotentiometric stripping p‐toluenesulfonic acid performs as well as the usual inorganic strong acids, particularly in terms of sensitivity. At 0.1 mol dm−3 it proved very suitable for the determination of toxic metals, in particular lead(II), at levels down to a few μg dm−3. The overall results appear promising and can open new avenues for preparing disposable cells for on‐field stripping chronopotentiometric determination of toxic metals.

Stripping potentiometry of indium in aqueous chloride solutions

Stripping potentiometry (SP) has been used effectively for the determination of trace levels of several metal species in solution. Indium ion, which can be readily reduced and has a high solubility in mercury, can be determined directly using SP. The reduction potential of indium is located between those of lead and cadmium, necessitating optimization of several experimental parameters for successful quantitative analysis. A method for the SP of In(III) is presented which utilizes constant current stripping analysis (CCSA) at a mercury-film glassy carbon electrode in KCl solutions in the presence of Pb(II) and Cd(II).

Polypyrrole Coated Mercury Film Electrodes for Sono-ASV Analysis of Cadmium and Lead

The feasibility of using reduced polypyrrole (PP), poly(acenaphtho[1,2-c]pyrrole) (PANP), and poly(4,9-dihydro-o-benzenonaphtho[2,3-c] pyrrole) (PDBNP) coated mercury thin film glassy carbon electrodes for the anodic stripping voltammetric determination of cadmium and lead in the presence of ultrasound is examined. The magnitude of the stripping peak for a given solution of cadmium and lead in 0.1 M acetate buffer at the polymer coated electrodes was found to follow the order of PDBNP>PANP>PP. This is rationalized in terms of the structure of the polymer chains. The influence of surfactants on the stripping response was investigated. Four types of surfactant were examined: sodium dodecyl sulfate (SDS), Triton X-100 (TX), bovine serum albumin (BSA), and dodecyl pyridinium chloride (DPC). While each was found to have a deleterious effect on peak height, it was found that the PDBNP coated electrode performed well in the presence of SDS solution. The three mercury film glassy carbon electrodes were found to be mechanically resistant under sonication as shown by atomic force microscopy (AFM).

Membrane electrodes can modulate the electrochemical response of redox proteins—direct electrochemistry of cytochrome c

Membrane (carbon or gold) electrodes constructed from dialysis membranes varying in cutoff and charge are used to investigate the electrochemical behavior of c-type cytochromes, especially cytochrome c. It is shown from cyclic voltammetry experiments that cytochrome c exhibits direct electrochemical responses at negatively charged membrane (graphite-, glassy carbon-, mercury film glassy carbon-, and gold) electrodes. Different factors (pre-treatment of the membrane, effect of positively charged species, ionic strength, pH, effect of the entrapped layer thickness) have been examined. The electrochemical response of multiheme cytochromes c3 at the membrane electrode is also investigated. It is demonstrated that the electrochemistry of cytochrome c at the membrane electrodes is essentially governed by favorable electrostatic interactions, and that other factors (especially adsorption and the presence of denatured forms) do not play a dominant role. A discussion on the electrochemistry of c-type cytochromes is given.

Substituted catechols as complexing agents for the determination of bismuth, lead, copper and cadmium by adsorptive stripping voltammetry

Copper, cadmium, lead and bismuth (> 5 μg ml −1) are determined by adsorptive cathodic stripping voltammetry (AdCSV) on a mercury film glassy carbon electrode, using catechol, 4-methylcatechol, 4- t-butylcatechol and resorcinol as complexing ligands. Complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4- t-butylcatechol showed the lowest current response. Cadmium showed a different behaviour from the other three metals in that the highest current response was observed with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper.

Stripping Potentiometry of Lead, Cadmium and Copper at a Nafion Coated Glassy Carbon Electrode with Encapsulated Mercury Acetate

The stripping potentiometric determination of lead, cadmium and copper with mercury film glassy-carbon electrodes coated with a Nafion membrane was investigated. The mercury film was plated using either mercury(II) acetate encapsulated within the Nafion membrane or a mercury(II) solution. Dissolved dioxygen was used as the stripping agent. The electrodes showed promising properties, particularly robustness and response repeatability. A linear dependence of the stripping time on concentration was found in the μg l−1 concentration range (s.d. of intercept ≤ 0.3 μg l−1, r.s.d. of slope ≤ 1%, for both lead and cadmium).

Voltammetric determination of the metal complexing capacity in model solutions

Determination of the metal complexing capacity (MCC) has been carried out in model solutions of 0.55 mol l −1 NaCl using anodic stripping voltammetry by two different working electrode assemblies: Static Mercury Drop Electrode (SMDE) and Thin Mercury Film Glassy Carbon Disk Electrode (TMFGCDE). The separation of the reduction potentials of free ions and labile copper(II) complexes vs. the inert one (Cu-EDTA) at SMDE is achieved by the addition of l mg l −1 of Triton-X-100. The appropriate deposition potential for copper complexing capacity (CuCC) determination has been established from the pseudopolarograms. TMFGCDE yields better separation of those reduction processes, when thinner film of mercury is applied without addition of surfactants. The determination limit of 10 −7 mol l −1 CuCC with SMDE was found. The results obtained with model solution show lower CuCC values than expected. This can be attributed to the partial dissociation of an inert Cu-EDTA complex during the transport through a rather thick diffusion layer formed with SMDE devices. The determination limit of 10 −8 mol l −1 MCC (Cd, Pb, Cu) with TMFGCDE was found. The MCC values obtained in the model solution were higher than expected due to the cell's ‘blank capacity’.

Determination of metal–organic complexation in natural waters by SWASV with pseudopolarograms

AbstractA novel electrochemical method is described for the examination of metal–organic complexation in natural waters. The technique is based upon the comparison of square wave anodic stripping voltammetry (SWASV) ‘pseudopolarograms’ (current vs. deposition potential plots) for natural samples with those obtained for metal complexation with selected ‘model’ binding ligands at constant ionic strength. For electrochemically active zinc species in seawater, the pseudopolarogram approach allowed the estimation of thermodynamic stability constants (KML) within a stability constant window of approximately 104–106 M−1 up to ≥ 1015 M−1. For a natural rainwater sample, the pseudopolarogram indicated only one zinc class, probably a mixture of ‘free’ and/or inorganically complexed species. In an application to a coastal seawater sample, three species were identified: (1) weakly complexed, log KZnL = 4.14 ± 0.92 M−1; (2) moderately complexed, log KZnL = 7.77 ± 0.62 M−1; (3) strongly complexed, log KZnL = 11.45 ± 0.95 M−1. Results are compared to those obtained using complexometric titration with SWASV at a thin mercury film–glassy carbon rotating disk (TMF–GCRD) electrode. The latter detected a single strong complexing ligand (or ligand class), with [L′] = 15.25 ± 0.04 nM and log K′ZnL ≥ 10.9 M−1.

Application of galvanic stripping analysis to trace determination of tin

A simple, rapid and reliable procedure for the determination of tin by galvanic stripping analysis is described. The determination includes (i) preconcentration of tin onto preformed mercury film glassy carbon electrode, and (ii) re-oxidation in open-circuit position by advantageously utilizing the localized galvanic couple formation (in the absence of external electrical field or oxidant in solution). The details of the development of such a procedure and its application to the determination of tin in pure zinc materials are discussed.

The differential pulse anodic stripping voltammetry of copper and lead and their determination in EDTA extracts of soils with the mercury film glassy carbon electrode

The differential pulse anodic stripping voltammetry of copper and lead at the mercury film glassy carbon electrode is discussed. The mercury film prevents the occurrence of a monolayer stripping peak for copper. The influence of antimony and bismuth on the anodic stripping voltammetric behaviour of copper and lead is discussed. An interaction between copper and antimony distorts the copper stripping peak and gives rise to an intermediate peak. The method described is suitable for determining copper and lead simultaneously in EDTA extracts of soils.

Comparison of linear scan and differential pulse anodic stripping voltammetry at a thin mercury film glassy carbon electrode

The use of the differential pulse mode in anodic stripping voltammetry with an electrode consisting of a thin mercury film deposited in situ on a glassy carbon support leads to detection limits which are 3–5 times lower than if a simple linear scan is used at the same electrode. If the glassy carbon electrode has a high base current, the improvement in detection limit with differential pulse will be even greater. Differential pulse peak currents, however, are more susceptible to interference by surface-active substances, and undetected adsorption/desorption effects can cause serious errors. Precautions which are necessary to maintain a glassy carbon electrode in good condition are described.

Anodic stripping voltammetry in a flow-through cell with fixed mercury film glassy carbon disc electrodes part II. The differential mode (D.A.S.V.)

Anodic stripping voltammetry in a flow-through cell with fixed mercury film glassy carbon disc electrodes part II. The differential mode (D.A.S.V.)

Anodic stripping voltammetry in a flow-through cell with fixed mercury film glassy carbon disc electrodes part II. the differential mode (D.A.S.V.)

Differential anodic stripping voltammetry at a fixed glassy carbon disc electrode covered by a thin mercury film, was adapted for use in a flow-through cell. Improved sensitivity, arising from virtually perfect compensation of background currents, is demonstrated by presenting the application of the method to the determination of heavy metal ions (hydrates and/or in a labile complex form), in the 0.1–1 ng ml −1 concentration range, in sea water, using short (1–6 min) deposition periods. Good precision of results is maintained; calibration curves, within the a.m. concentration range, are linear. Due to simplicity and stability, the system seems well suited for continuous monitoring in aqueous media.

Anodic stripping voltammetry in a flow-through cell with a fixed mercury film glassy carbon disc electrode. Part I

Anodic stripping voltammetry at a glassy carbon disc electrode covered by a thin mercury film was adapted for use in a flow-through cell. The resulting system is characterized by extreme simplicity of set-up and operation, high sensitivity and excellent precision and stability. Its performance was tested via the determination of hydrated or labile complex ions of heavy metal ions in sea water, using short (2–10 min) deposition periods. The dependence of the stripping peak charge on metal ion concentration, length of deposition period, solution flow rate and other variables was examined and the reliability of the results obtained were evaluated under conditions resembling continuous monitoring.

Anodic stripping voltammetry in a flow-through cell with a fixed mercury film glassy carbon disc electrode. Part I

Anodic stripping voltammetry at a glassy carbon disc electrode covered by a thin mercury film was adapted for use in a flow-through cell. The resulting system is characterized by extreme simplicity of set-up and operation, high sensitivity and excellent precision and stability. Its performance was tested via the determination of hydrated or labile complex ions of heavy metal ions in sea water, using short (2–10 min) deposition periods. The dependence of the stripping peak charge on metal ion concentration, length of deposition period, solution flow rate and other variables was examined and the reliability of the results obtained were evaluated under conditions resembling continuous monitoring.

Electrochemical Studies on Complexation and Speciation of Copper(II) in ppb Level with 1,10-Phenanthroline in Aqueous Media

Complexation and speciation of copper (II) in ppb level with 1,10-phenanthroline (L) in aqueous media have been investigated by differential pulse anodic stripping voltammetry using thin mercury film glassy carbon electrode (TMFGCE). The work was carried out at constant ionic strength of 0.01 mol dm-3 using NaNO3 at ambient temperature. The pH was kept constant at 9.12 ± 0.10 by the addition of borate buffer. Applying the concept of DeFord and Hume, the stability constants of different species of copper with 1,10-phenanthroline were calculated from the variation of peak potential and diffusion current of simple and complexed metal ions under the present experimental conditions. It was found that copper(II) form three complexes (1:1, 1:2 and 1: 3; metal : ligand) with 1,10-phenanthroline. The overall stability constant of copper complexes, MLn can be defined as βMLn= [MLn ]/[M2+][L]n in which M2+ = Cu2+ and L = 1,10-phenanthroline; n is an integer. The values of the stability constant of different copper complexes with 1,10-phenanthroline were found to be 109.33, 1015.10 and 1020.48 for CuL, CuL2 and CuL3, respectively (the overall charges were omitted for simplicity). The high values of overall stability constant indicate that the complexes are highly stable. Using the values of stability constant of copper complexes and hydrolysis constant of copper, the percentage of all possible copper species under present experimental conditions were calculated. Keywords: Electrochemical; Speciation; Complexation; Copper 1,10-phenanthroline. DOI: http://dx.doi.org/10.3329/bjsir.v46i2.8188 Bangladesh J. Sci. Ind. Res. 46(2), 219-224, 2011