Anastasios Voulgaropoulos

A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair

This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low mug l(-1) concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at -1.4 V on a rotating glassy carbon disk electrode. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from -1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 mug l(-1) for Cd and for Pb and 0.7 mug l(-1) for Zn at a preconcentration time of 10 min. Finally, BFEs were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS).

A study of Nafion-coated bismuth-film electrodes for the determination of trace metals by anodic stripping voltammetry

This work reports on the fabrication, characterization and applications of Nafion-coated bismuth-film electrodes (NCBFEs) for the determination of trace metals by anodic stripping voltammetry (ASV). A NCBFE was typically prepared by first applying a 5 microl drop of a 1% Nafion solution onto the surface of a glassy-carbon rotating-disk electrode. After evaporation of the solvent, the Bi film was plated on the electrode in situ(i.e. by spiking the sample with 1000 microg l(-1) of Bi(iii) and simultaneous electrolytic deposition of the metal ions and bismuth film on the electrode surface at -1.4 V) or ex-situ(i.e. by electrolytic deposition of the bismuth film in a separate solution containing 1000 microg l(-1) of Bi(iii), followed by the ASV measurement step in the sample solution). Various fabrication and operational parameters were thoroughly investigated and discussed in terms of their effect on the ASV signals. It was found that this voltammetric sensor was suitable for the determination of metals at trace levels by square-wave ASV (SWASV) due to its multi-element detection potential, improved analytical sensitivity, high resistance to surfactants, low cost, ease of fabrication, robustness, speed of analysis and low toxicity (as compared to traditional mercury electrodes). In the presence of 4 mg l(-1) of Triton X-100, the NCBFE afforded a 10-fold peak height enhancement for the Pb peak and a 14-fold enhancement for the Cd peak over a bare BFE while the determination of Zn was feasible only on the NCBFE. The limits of detection (at a signal-to-noise ratio of 3) were 0.1 microg l(-1) for Cd and Pb and 0.4 microg l(-1) for Zn for a deposition time of 10 min. Finally, the electrode was applied to different real samples (tap-water, urine and wine) for the analysis of trace metals with satisfactory results.

On-line stripping voltammetry of trace metals at a flow-through bismuth-film electrode by means of a hybrid flow-injection/sequential-injection system.

In this work, we describe an automated stripping analyzer operating on a hybrid flow-injection/sequential-injection (FIA/SIA) mode and utilizing a bismuth-film electrode (BiFE) as a flow-through sensor for on-line stripping voltammetry of trace metals. The instrument combines the advantages of FIA and SIA and is characterised by simplicity, low-cost, rapidity, versatility and low consumption of solutions. The proposed analytical flow methodology was applied to the determination of Cd(II) and Pb(II) by anodic stripping voltammetry (ASV) and of Ni(II) and Co(II) by adsorptive stripping voltammetry (AdSV). The steps of the rather complex experimental sequence (i.e. the bismuth-film formation, the analyte accumulation, the voltammetric stripping and the electrode cleaning/regeneration) were conducted on-line and the critical parameters related to the respective analytical procedures were investigated. In ASV, for a accumulation time of 180s the limits of detection for Cd(II) and Pb(II) were 2 and 1microg l(-1), respectively (S/N=3) and the relative standard deviations were 5.3% and 4.7%, respectively (n=8). In AdSV, for a total sample volume of 1000microl, the limits of detection for Ni(II) and Co(II) were 1microg l(-1) (S/N=3) and the relative standard deviations were 5.5% and 6.2%, respectively (n=8). The measurement frequency ranged between 15 and 20 stripping cycles h(-1). The results indicate that the BiFE is well suited as a flow-through detector for on-line stripping analysis and, by virtue of its low toxicity, can serve as a viable alternative to mercury-based flow-through electrodes.

Study of interactions between DNA-ethidium bromide (EB) and dna-acridine orange (AO), in solution, using hanging mercury drop electrode (HMDE)

The interaction of ethidium bromide (EB) and acridine orange (AO) with double stranded (ds), thermally denatured (ss) and supercoiled (sc) DNA, in solution, was studied by alternating current voltammetry (AC voltammetry) at the hanging mercury drop electrode (HMDE) in 0.3 M NaCl+50 mM sodium phosphate buffer (pH 8.5). Their interaction with DNA is shown to be time dependent and completely different. The changes at peak 2 (peak at -1.20 V) of dsDNA form and the appearance of peak 3 (peak at -1.42 V) in scDNA form are presented as criteria declaring the different mechanism of interaction of EB and AO with DNA. Additionally, the appearance of a new peak at around -0.44 V as a result of DNA and AO interaction, differentiates the studied behaviors. The comparison of the electrochemical behaviors of these compounds highlights the differences in the mechanism of interaction.

A study of the determination of the hypertensive drug captopril by square wave cathodic adsorptive stripping voltammetry.

In this work, the determination of captopril (CPL) was studied by square wave cathodic adsorptive stripping voltammetry (SWCAdSV) on a hanging mercury drop electrode (HMDE). CPL was adsorptively preconcentrated on the mercury surface as a sparingly soluble mercury salt under stirring of the solution and then the accumulated species was reduced by a cathodic square wave voltammetric scan. The reduction current was related to the CPL concentration in the sample. The chemical and instrumental parameters affecting the response were investigated and optimized for the CPL determination. The calibration curve was linear from 0.5 to 180 microg l(-1) of CPL (depending on the preconcentration time), the limit of detection at a S/N ratio of 3 was 0.5 microg l(-1) with 300 s of preconcentration and the relative standard deviation was 3.2% at the 20 microg l(-1) level (with 120 s of preconcentration, n=8). The method was applied to the determination of CPL in two pharmaceutical formulations with recoveries of 97.9 and 98.8%. Finally, the potential for applying the proposed method to the determination of CPL in biological media is briefly discussed.

Study of interactions between actinomycin D and DNA on carbon paste electrode (CPE) and on the hanging mercury drop (HMDE) surface

The interaction of actinomycin (ACTD) with double stranded (ds) calf thymus DNA and single stranded (ss) DNA was studied at the carbon paste electrode surface by means of transfer voltammetry in 0.2 M phosphate buffer solution (pH 7.4). Accordingly the interaction of actinomycin (ACTD) with ds calf thymus DNA, ss DNA and supercoiled (sc) DNA was studied using hanging mercury drop electrode in 0.3 M NaCl, and 50 mM sodium phosphate buffer (pH 8.5). The different electrochemical behaviours are presented and compared in the article.

Analysis of sulphonated azodyes and their degradation products in aqueous solutions treated with a new electrochemical method

Aqueous solutions of four sulphonated azodyes, Reactive Orange 91, Reactive Red 184, Reactive Blue 182 and Reactive Black 5, containing 0.2 mol/L of electrolyte were treated in a laboratory scale electrolytic cell with a new electrochemical method intended for the textile wastewater treatment. The electrochemical process was monitored by means of absorbance of UV-Vis light and chemical oxygen demand values. Carbon fleece was used as a cathode, and platinated titanium was used as an anode. Reversed-phase high-performance liquid chromatography coupled with photodiode array and mass spectrometric detectors was applied for the analysis of dyes, their impurities and degradation products after the electrochemical treatment. Dihexylammonium and triethylammonium acetate as ion-pairing reagents, or alternatively ammonium acetate as an ion-exclusion suppressing reagent, were used to improve the separation.

Amperometric determination of cyanides at the low ppb level by automated preconcentration based on gas diffusion coupled to sequential injection analysis.

A simple, sensitive method for determining free cyanides is described. The assay is based on automated gas diffusion of the analyte using sequential injection analysis (SIA) coupled to amperometric detection on a silver working electrode. The effects of varying several parameters affecting the analytical procedure (including the flow rates of the donor and acceptor streams, the concentrations of the reagents and the sample volumes) were studied. The validity and quality of the method were also assessed, by examining its linearity, limits of detection and quantitation, precision, selectivity to potentially interfering substances. Its sensitivity can be enhanced by applying a simple preconcentration step, following which limits of detection were found to be 0.05-0.12 microgL(-1). Application of the proposed assay to the analysis of tap, mineral and table water samples spiked at concentrations ranging from 1 to 10 microgL(-1) CN(-), yielded satisfactory recoveries (88-112%).

Coupling of sequential injection with liquid chromatography for the automated derivatization and on-line determination of amino acids.

The principle of sequential injection (SI) was exploited to develop a fully automated pre-column derivatization procedure combined on-line to liquid chromatography (LC). Using SI-LC derivatization 14 amino acids were determined fluorimetrically in pharmaceuticals with o-phthaldialdehyde (OPA) as the derivatization reagent. The SI system was used for the handling of samples and reagents, on-line mixing and introduction to the LC injection system. Chemical (pH and reagents concentrations) and instrumental variables (sample and reagent volumes, reaction time and flow rate) were optimized to attain the highest reaction yield and detector signal. Reversed phase chromatographic resolution of 14 amino acids was achieved within 35min using gradient elution. The automated operation of the coupled SI-LC system resulted in very satisfactory performance. The method was applied for the simultaneous determination of amino acids in pharmaceutical formulations.

Synthesis and characterization of LiMn2O4 for use in Li-ion batteries

Lithiated spinel manganese dioxide was synthesised from electrochemical MnO 2 and Li2CO 3 with deficiency or excess lithium (Li x Mn 2 O 4 , 0.8 <x < 1.3) for use in Li/Li x Mn 2 O 4 and Li-ion cells. Micron-sized Li 1.05 Mn 2 O 4 prepared at 730°C showed high Li utilization, excellent cyclability and good rate capability with an initial discharge capacity of 123 mA h/g and 10% discharge capacity reduction after 20 cycles. Different types of commercial carbonaceous materials were also investigated with respect to their electrochemical performance vs. Li. Unoptimised Li-ion cells, using Li 1.05 Mn 2 O 4 prepared at 730°C as the cathode material, EC-DMC-LiPF 6 electrolyte and carbon fibres, showed promising performance characteristics.