Cathodic stripping voltammetric determination of ceftazidime with reactive accumulation at a poly-L-lysine modified hanging mercury drop electrode

Ceftazidime is hydrolysed only slowly at pH 10 at room temperature. This is indicated by a small cathodic stripping voltammetric peak obtained at pH 10 at a hanging mercury drop electrode at about -0.6 V which corresponds to the reduction of the hydrolysis product. This peak is enhanced more than tenfold by the addition of poly-L-lysine (PLL) to the electrolyte solution. The optimum accumulation potential is between 0 and -0.1 V: the size of the peak decreases steadily, however, as the accumulation potential is moved to more negative potentials and is about one-sixth the size for accumulation at -0.4 V. Existing knowledge of the organic chemistry of cephalosporins indicates that the accumulation must involve an aminolysis reaction of the unprotonated PLL with the beta-lactam ring of the ceftazidime. The limit of detection (3 sigma) in standard solutions was calculated to be 1 x 10(-10) mol l(-1). The detection limit in buffer solution containing 1% of urine was calculated to be 5 x 10(-9) mol l(-1), i.e. 5 x 10(-6) mol l(-1) in the urine. (C) 1999 Elsevier B.V. B.V. AU rights reserved.

Aspects of cathodic stripping voltammetry at the hanging mercury drop electrode and in non-mercury disposable sensors

Cathodic stripping voltammetry (CSV) and accumulation at the hanging mercury drop electrode are reviewed briefly. Proposals in a recent IUPAC technical report are considered. Three recent developments in CSV are discussed: the adaptation of CSV methods developed for use with the hanging mercury drop electrode for use with screen-printed carbon electrodes in disposable sensors, the use of reactive accumulation, and the chemometric use of kinetic methods of determination with pulse methods in CSV.

A Solid Film Electrode of Intermetallic Ag 2 Hg 3.02 for the Direct Determination of Folic Acid in Fresh and Processed Fruit Juices

AgSIE was used for the direct analysis of folic acid (FA), with a detection limit and lower level of quantitation of 6.8 x10-10 mol L-1 and 2.3 x 10 8 mol L-1. The analysis in fresh and processed fruits was done without any sample pretreatment. In strawberry and acerola juices, FA concentration level values were below the method detection limit. FA was detectable in peach (77.7 0.4 mg L-1 and 64.4 0.5 mgL-1), Persian lime (45.4 0.7 mg L-1), pineapple Hawaii (66.2 0.4 mgL-1), pear pineapple (35.3 0.6 mgL-1), cashew (54.4 0.5 mgL-1) , passion fruit (73.2 0.3 mgL-1), and apple (84.4 0.5 mg L-1 ).

Desenvolvimento de eletrodos modificados para determinação de compostos sulfurados em gasolina

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

(Table 2) Concentrations of dissolved Zn, Cd, Pb, and Cu in waters of the Baltic Sea

A method of determination of low concentrations of zinc, cadmium, lead, and copper dissolved in seawater and interstitial water with use of inversion voltammetry with AC solution conditions is described. The optimum conditions for measurements with accumulation on a mercury-film electrode with a silver substrate are presented. Detection limit is 0.2 ?g/l for zinc and 0.05 ?g/l for cadmium, lead, and copper. Large number of determinations can be carried out during expeditions at natural pH of seawater containing these four metals.

Fast ultrasound-assisted treatment of urine samples for chronopotentiometric stripping determination of mercury at gold film electrodes

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HCl and H2O2 for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators. (c) 2006 Elsevier B.V. All rights reserved.

Ex Situ Scanning Electrochemical Microscopy (SECM) Investigation of Bismuth- and Bismuth/Lead Alloy Film-Modified Gold Electrodes in Alkaline Medium

Scanning electrochemical microscopy (SECM) in feedback mode was employed to characterise the reactivity and microscopic peculiarities of bismuth and bismuth/lead alloys plated onto gold disk substrates in 0.1 molL(-1) NaOH solutions. Methyl viologen was used as redox mediator, while a platinum microelectrode was employed as the SECM tip. The metal films were electrodeposited ex situ from NaOH solutions containing either bismuth ions only or both bismuth and lead ions. Approach curves and SECM images indicated that the metal films were conductive and locally reactive with oxygen to provide Bi(3+) and Pb(2+) ions. The occurrence of the latter chemical reactions was verified by local anodic stripping voltammetry (ASV) at the substrate solution interface by using a mercury-coated platinum SECM tip. The latter types of measurements allowed also verifying that lead was not uniformly distributed onto the bismuth film electrode substrate. These findings were confirmed by scanning electron microscopy images. The surface heterogeneity produced during the metal deposition process, however, did not affect the analytical performance of the bismuth coated gold electrode in anodic stripping voltammetry for the determination of lead in alkaline media, even in aerated aqueous solutions. Under the latter conditions, stripping peak currents proportional to lead concentration with a satisfactory reproducibility (within 5% RSD) were obtained.

Thermal analysis and electrochemical study of Hg reactions on Pt-30% Ir alloy electrode

Thermogravimetry (TG), cyclic voltammetry (CV) and other analytical techniques were used to study the reactions of mercury with Pt-30% Ir alloy. The results allowed to suggest that an electrodeposited mercury film interacts with the substrate and when subjected to heat or electrochemical removal at least four mass loss steps or five peaks appeared during the mercury desorption process. The first two steps were attributed to Hg(0) removal probably from the bulk and from the adsorbed monolayer which wets the electrode surface. These two processes are responsible for peaks D and F in the cyclic voltammograms. The last two peaks (G, H) in CV were ascribed to the intermetallic compound decomposition. In TG curves, the last two steps were attributed to the PtHg4 (third step), and PtHg2 decomposition followed by Hg removal from the subsurface. The PtHg2 was formed by an eutectoide reaction: PtHg -> PtHg2+Hg(Pt-Ir). The Hg diffused to the subsurface was not detectable by cyclic voltammetry.

Scanned stripping chronopotentiometry at bismuth film rotating disc electrodes: a method for quantitative dynamic metal speciation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A systematic procedure to enhance reproducibility of SWASV cycles in the determination of toxic metals in real samples

This work presents for the first time a systematic study on the optimization of the electrochemical cleaning time of a mercury film when it is used as a working electrode material in the analysis of toxic metals, such as Pb2+, used as model metal, in real samples by SWASV. The optimization study for the film’s cleaning time aimed at attaining a Pb2+ minimum value in the film after the re-oxidation step of the pre-concentrated metal, given the impossibility of complete removal of traces of the electroactive species from the film. This value was kept constant in each concentration range studied ensuring thus that all assays were performed in initial identical conditions. An assay performed on a synthetic sample was taken as reference. In it, given the absence of matrix effects, and after the electrochemical cleaning step, a direct proportionality was observed between the residual amounts of Pb2+ in the film (which for the cleaning time used was never completely removed) and Pb2+ concentration in the solution. This fact determined a high correlation between Pb2+ peak current and Pb2+ concentration which was not observed when real samples (tree leaves) were analyzed. This behavior may result from the presence of the interfering surfactants always present in real samples of complex matrix. Cleaning time optimization was performed for the following Pb2+ concentration ranges in the real samples of complex matrix: 0.006-0.020, 0.020-0.080, 0.060-0.200 and 0.100-0.600 ppb. As expected, in order to obtain identical levels of film’s cleaning efficiency, the need for longer cleaning times has been observed for higher concentrations. The optimized cleaning times for the concentration ranges under study were 120, 150, 180 e 300 s, respectively.

Estabilização de solo contaminado com zinco usando zeólitas sintetizadas a partir de cinzas de carvão

The effect of synthetic zeolites on stabilizing Zn-contaminated soil using 0.01 mol L-1 CaCl2 leaching solution in batch experiments was investigated. The zeolites were synthesized from coal ash by hydrothermal treatment with alkaline solution. The additive enhanced the sorption capacity of the soil and reduced leaching. Zinc leaching was reduced by more than 80% using a minimum of 10% additive. The higher cation exchange capacity of the zeolite/soil mixtures and higher pH were responsible for stabilizing Zn in soil. The poly(2-aminobenzenesulfonic acid)-coated mercury thin-film electrode was used for the determination of zinc.

Ruthenium oxide hexacyanoferrate modified electrode for hydrogen peroxide detection

A sensor for H2O2 amperometric detection based on a Prussian blue (PB) analogue was developed. The electrocatalytic process allows the determination of hydrogen peroxide at 0.0 V with a limit of detection of 1.3 mu mol L-1 in a flow injection analysis (FIA) configuration. Studies on the optimization of the FIA parameters were performed and under optimal FIA operational conditions the linear response of the method was extended up to 500 mu mol L-1 hydrogen peroxide with good stability. The possibility of using the developed sensor in medium containing sodium ions and the increased operational stability constitute advantages in comparison with PB-based amperometric sensors. The usefulness of the methodology was demonstrated by addition-recovery experiments with rainwater samples and values were in the 98.8 to 103% range.

Indirect cathodic-stripping voltammetric determination of ceftazidime as a mercury salt

At accumulation potentials close to +0.1 V at a hanging mercury drop electrode, ceftazidime is accumulated at pH 9.5, probably in a hydrolysed or otherwise chemically altered form, in an anodic process to give an adsorbed mercury salt. The accumulation of this mercury salt allows the indirect cathodic-stripping voltammetric determination of ceftazidime using the reduction peak of the mercury salt at -0.70 V. The high sensitivity of the method coupled with high sample dilution allows ceftazidime to be determined in milk samples at the 28 mu g ml(-1) level without prior separation. In order to determine lower levels of ceftazidime in milk (ca. 10 ng ml(-1)) a separation process would be required. (C) 1998 Elsevier B.V. B.V. All rights reserved.

Evaluation of color removal and degradation of a reactive textile azo dye on nanoporous TiO2 thin-film electrodes

The feasibility of the photobleaching of a textile azo dye, reactive orange 16 (C.I. 17757), in aqueous solution using titanium dioxide thin-film electrodes prepared by the sol-gel method was investigated. The best conditions for maximum photoelectrocatalytic degradation were found to be pH > 10 for Na2SO4 medium and pH < 6 for NaCl. In both situations, an applied potential of +1.0 V and low dye concentration are recommended, when 100% of color removal is obtained after 20 min of photoelectrocatalysis. The effects of side reaction pathway on the degradation rate of dye in sulfate and chloride medium were presented and the best performance are optimized to situations closed to that verified in the textile effluent. The influence of variables as applied potential, pH, supporting electrolyte and dye concentration on the kinetics of photoelectrochemical degradation also were investigated. Oxalic acid is identified by HPLC and UV-Vis spectrophotometric methods as the main degradation product generated after 180 min of photoelectrocatalysis of 4 x 10(-5) mol l(-1) dye in sodium sulphate pH 12 and NaCl pH 4.0 and a maximum reduction of 56 and 62% TOC was obtained, respectively. (C) 2004 Elsevier Ltd. All rights reserved.

Electrodeposited thin mercury films on Pt-Ir alloy electrodes

Mercury thin films prepared by electrochemical deposition on Pt-Ir alloy and after partial removing of mercury at different temperatures were studied by means of an interferometric surface mapping microscope and by X-ray photoelectronic spectroscopy. Mercury film samples having mercury partially removed by anodic stripping at a potential more positive than the corresponding peak in the voltammogram were also studied using the same techniques. For blank samples the surface topographic studies showed well defined grain boundaries. Mercury film samples when heated up to different temperatures showed as material is removed and that the surface roughness decreases as the temperature increases. For samples heated up to 800 degrees C the surface roughness is approximately the same that for the blank. A model for the interphase of volumetric mercury electrodeposited on a Pt-Ir alloy has been proposed using samples both electrochemically and thermally removed of their Hg coatings. The model includes a layered three-region structure, containing at least two Pt-Hg intermetallics: PtHg4 and PtHg2. A substrate modified region, iridium rich, has also been detected. (C) 1999 Elsevier B.V. S.A. All rights reserved.