Quantification of N-acetylcysteine in pharmaceuticals using cobalt phthalocyanine modified graphite electrodes

Flow injection analysis (FIA) with amperometric detection was employed for the quantification of N-acetylcysteine (NAC) in pharmaceutical formulations, utilizing an ordinary pyrolytic graphite (OPG) electrode modified with cobalt phthalocyanine (CoPc). Cyclic voltammetry was used in preliminary studies to establish the best conditions for NAC analysis. In FIA-amperometric experiments the OPG-CoPc electrode exhibited sharp and reproducible current peaks over a wide linear working range (5.0 x 10(-5)-1.0 x 10(-3) mol L(-1)) in 0.1 mol L(-1) NaOH solution. High sensitivity (130 mA mol(-1) cm(2)) and a low detection limit (9.0 x 10(-7) mol L(-1)) were achieved using the sensor. The repeatability (R.S.D.%) for 13 successive flow injections of a solution containing 5.0 x 10(-4) mol L(-1) NAC was 1.1%. The new procedure was applied in analyses of commercial pharmaceutical products and the results were in excellent agreement with those obtained using the official titrimetric method. The proposed amperometric method is highly suitable for quality control analyses of NAC in pharmaceuticals since it is rapid, precise and requires much less work than the recommended titrimetric method. (C) 2010 Elsevier B.V. All rights reserved.

Electrocatalytic behavior of glassy carbon electrodes modified with multiwalled carbon nanotubes and cobalt phthalocyanine for selective analysis of dopamine in presence of ascorbic acid

This work describes the development, electrochemical characterization and utilization of a cobalt phthalocyanine modified carbon nanotube electrode for the quantitative determination of dopamine in 0.2 mol L-1 phosphate buffer contaminated with high concentration of ascorbic acid. The electrode surface was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy which showed a modified surface presenting a charge transfer resistance of 500 Omega, against the 16.46 k Omega value found for the bare glassy carbon surface. A pseudo rate constant value of 5.4 x 10(-4) cm s(-1) for dopamine oxidation was calculated. Voltammetric experiments showed a shift of the peak potential of DA oxidation to less positive value at 390 mV as compared with that of a bare GC electrode at 570 mV. The electrochemical determination of dopamine, in presence of ascorbic acid in concentrations up to 0.1 mol L-1 by differential pulse voltarnmetry, yielded a detection limit as low as 2.56 x 10(-7) mol L-1.

Electrochemical and spectroscopic characterization of screen-printed gold-based electrodes modified with self-assembled monolayers and Tc85 protein

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

Label-free DNA detection of hepatitis C virus based on modified conducting polypyrrole films at microelectrodes and atomic force microscopy tip-integrated electrodes

We present a new strategy for the label-free electrochemical detection of DNA hybridization for detecting hepatitis C virus based on electrostatic modulation of the ion-exchange kinetics of a polypyrrole film deposited at microelectrodes. Synthetic single-stranded 18-mer HCV genotype-1-specific probe DNA has been immobilized at a 2,5-bis(2-thienyl)-N-(3-phosphoryl-n-alkyl)pyrrole film established by electropolymerization at the previously formed polypyrrole layer. HCV DNA sequences (244-mer) resulting from the reverse transcriptase-linked polymerase chain reaction amplification of the original viral RNA were monitored by affecting the ion-exchange properties of the polypyrrole film. The performance of this miniaturized DNA sensor system was studied in respect to selectivity, sensitivity, and reproducibility. The limit of detection was determined at 1.82 x 10(-21) mol L-1. Control experiments were performed with cDNA from HCV genotypes 2a/c, 2b, and 3 and did not show any unspecific binding. Additionally, the influence of the spacer length of 2,5-bis(2-thienyl)-N-(3-phosphoryl-n-alkyl)pyrrole on the behavior of the DNA sensor was investigated. This biosensing scheme was finally extended to the electrochemical detection of DNA at submicrometer-sized DNA biosensors integrated into bifunctional atomic force scanning electrochemical microscopy probes. The 18-mer DNA target was again monitored by following the ion-exchange properties of the polypyrrole film. Control experiments were performed with 12-base pair mismatched sequences.

Study of zinc hexacyanoferrate-modified platinum electrodes using electrochemical quartz crystal microbalance

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Characterization of electrodes chemically modified with Mn(III) porphyrin/polypyrrole films as catalytic surfaces for an azo dye

In this study we describe the electrochemical behavior of 5,10,15,20-tetrakis(2'-aminophenylporphyrin)manganese(III) chloride supported on a glassy carbon electrode, as well as the electrochemical preparation and characterization of thin films based on pyrrole-3-carboxylic acid. The electrocatalytic action of the electrode modified with the Mn(III) porphyrin toward an azo dye was tested, and the characteristic strong interaction between the incorporated metalloporphyrin and RR120 dye was verified. Copyright (c) 2006 Society of Porphyrins & Phthalocyanines.

Anodic oxidation of formaldehyde on Pt-modified SnO2 thin film electrodes prepared by a sol-gel method

Pt-modified SnO2 electrodes were prepared onto titanium substrates in the form of thin films of similar to2 mum at different temperatures in the range from 200 to 400degreesC. Surface morphology was examined by scanning electron microscopy (SEM). It was found that Pt-SnO2 sol-gel layers are significantly rough and have a low porosity. X-ray diffraction (XRD) studies showed that the films consist of Pt nanoparticles with average size varying from about 5 to 10 nm, depending on the preparation temperature, and amorphous tin oxide. X-ray photoelectron spectroscopy (XPS) was employed to determine the superficial composition of the electrodes and demonstrated the presence of Sn4+ in all the samples. XPS spectra of the Pt 4f electrons showed the presence of Pt in the zero-valence state as well as in ionic forms. The general electrochemical behavior was characterized by cyclic voltammetry in 1 mol l(-1) HClO4 and the electrocatalytic activity towards the oxidation of formaldehyde was investigated by potential sweeps and chronoamperometry. The results obtained show that the Pt-SnO2/Ti system exhibits a significant catalytic activity for the oxidation of formaldehyde, with an onset potential below 0.1 V. (C) 2004 Elsevier Ltd. All rights reserved.

Selective UV-filter detection with sensors based on stainless steel electrodes modified with polyaniline doped with metal tetrasulfonated phthalocyanine films

This work describes the construction and application of two amperometric sensors for sensitive UV-filter determination. The sensors were prepared using stainless steel electrodes in which polyaniline (PANI) was electrochemically polymerized in the presence of nickel (NiPcTS) or iron (FePcTS) tetrasulfonated phthalocyanines. The sensor surface characterizations were carried out using atomic force microscopy (AFM). The PANI/NiPcTS sensor was selective for the chemical UV-filter p-aminobenzoic acid (PABA) and the PANI/FePcTS sensor was selective for octyldimethyl-PABA (ODP), both in a mixture of tetrahydrofuran (THF) and 0.1 mol L(-1) H(2)SO(4) at a volume ratio of 30 : 70, and with an applied potential of 0.0 mV vs. Ag vertical bar AgCl. A detailed investigation of the selectivity was carried out for both sensors, in order to determine their responses for ten different UV filters. Finally, each sensor was successfully applied to PABA or ODP quantification in sunscreen formulations and water from swimming pools.

Nanostructured screen-printed electrodes modified with self-assembled monolayers for determination of metronidazole in different matrices

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

The oxidation of hydroxylamine on Pt-, and Pd-modified Au electrodes in aqueous electrolytes: Electrochemical and in situ spectroscopic studies

The electrooxidation of hydroxylamine, NH2OH, in 0.1 M phosphate buffer (PB, pH = 7) on Pt-, and Pd-modified Au electrodes prepared by galvanic displacement of underpotential deposited Cu, was investigated by electrochemical techniques and three and in situ vibrational probes, substrate-induced surface enhanced Raman scattering, SI-SERS, surface enhanced infrared absorption, SEIRAS, and Fourier transform infrared reflection-absorption, IRAS, spectroscopies. Analyses of the results obtained made it possible to identify at low overpotentials, solution phase (sol) and adsorbed (ads) nitric oxide, NO, as well as solution phase nitrous oxide, N2O. As the potential was increased, the peak(s) ascribed to NO(ads) gained in intensity and new features associated with NO2−(ads) and NO2−(sol) were clearly discerned. Further excursion toward higher potentials yielded an additional peak assigned to NO2(ads). This behavior is analogous to that found for bare Au electrodes in a potential region in which the metal is at least partially oxidized under otherwise the same experimental conditions.

Multi-walled carbon nanotubes modified screen-printed electrodes for cisplatin detection

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electroanalytical detection of pindolol: comparison of unmodified and reduced graphene oxide modified screen-printed graphite electrodes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Mechanistic changes observed in heavy water for nitrate reduction reaction on palladium-modified Pt(hkl) electrodes

Reduction of nitrate on palladium-modified platinum single-crystal electrodes has been investigated both voltammetrically and spectroscopically in acidic media (pH = 1). Results obtained in H2O and D2O solvents are compared for the three crystallographic orientations. FTIR and differential electrochemical mass spectrometry (DEMS) results clearly indicate that the isotopic substitution of the solvent has a large effect in the mechanism of the reaction, changing the nature of the detected products. For Pt(111)/Pd and Pt(100)/Pd, N2O is detected as the main product of nitrate reduction when D2O is used as solvent, while no N2O is detected when the reaction is performed in H2O. For Pt(110)/Pd, N2O is detected in both solvents, although the use of D2O clearly favours the preferential formation of this product. The magnitude of voltammetric currents is also affected by the nature of the solvent. This has been analysed considering, in addition to the different product distribution, the existence of different transport numbers and optical constants of the solvent.