Unraveling the Role of Sulfur Compounds in Acid Rain Formation: Experiments on a Wetted Glass pH Electrode

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11 immobilized with Nafion film has been studied by means of cyclic voltammetry and rotating disk electrode techniques. The modified electrode shows high catalytic activity toward the reduction of both O-2 and H2O2. The rate constants of Oz and H2O2 reduction at the modified electrode have been measured and compared. It is found that O-2 undergoes a four-electron reduction at the modified electrode and the catalytic activity for the reduction of O-2 is dependent on the pH of the solutions.

Abnormal IR spectra of CO adsorbed on the surface of glass carbon electrode modified with polypyrrole film with platinum microparticles

Abnormal IR spectra of CO adsorbed at the surface of glass carbon electrode modified with polypyrrole film with Pt microparticles are reported.

Potentiometric determination of captopril in pharmaceutical formulations

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

Amperometric urea biosensors based on the entrapment of urease in polypyrrole films

Urease (Urs) was immobilized in electrochemically prepared polypyrrole (PPy) and the resulting films were characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet visible spectroscopy (UV-VIS). The enzymatic activity of Urs entrapped in the PPy matrix was confirmed by the catalytic conversion of urea into carbon dioxide and ammonia, when urea was detected amperometrically at different concentrations in standard samples and commercial fertilizers. The PPy/Urs biosensors exhibited selectivity, a relatively high efficiency at urea concentrations below 3.0 mmol L-1, and a sensitivity to urea of 2.41 mu A cm(-2) mmol(-1) L (C) 2011 Elsevier Ltd. All rights reserved.

New methodology for pH measurements in fuel ethanol using glass electrode

Studies carried out with glass electrode in anhydrous ethanol and ethanol-water solutions for measuring pH values have shown that this parameter depends on the solution composition, the contact time with the solution, the utilized temperature, and the type of electrolyte used. It was also observed that the glass electrode behavior in an acid medium differs from an alkaline medium. These studies provided correction factors for pH values from 2 to 12, allowing the realization of proper measurements of the hydrogen ionic activity in the ethanol-water and anhydrous ethanol solutions. However, these correction factors could not be applied to the fuel ethanol. Alternatively, a new method was developed for the correction of the pH values, which can be applied in hydrous and anhydrous fuel ethanol samples. Copyright © 2011 by ASTM International.

pH-dependent conformational changes of ferricytochrome c induced by electrode surface microstructure

pH-dependent processes of bovine heart ferricytochrome c have been investigated by electronic absorption and circular dichroism (CD) spectra at functionalized single-wall carbon 'nanotubes (SWNTs) modified glass carbon electrode (SWNTs/ GCE) using a long optical path thin layer cell. These methods enabled the pH-dependent conformational changes arising from the heme structure change to be monitored. The spectra obtained at functionalized SWNTs/GCE reflect electrode surface microstructure-dependent changes for pH-induced protein conformation, pK(a) of alkaline transition and structural microenvironment of the ferricytochrome c heme. pH-dependent conformational distribution curves of ferricytochrome c obtained by analysis of in situ CD spectra using singular value decomposition least square (SVDLS) method show that the functionalized SWNTs can retain native conformational stability of ferricytochrome c during alkaline transition.

The electronic detail of a digital pH-meter

This paperwork presents the complete circuitry used to build a microcontroller-based pH-meter. Key control software is also discussed. An industry-standard glass combination electrode has been employed for pH detection. Electrode parameter extraction procedure is presented. Good measurement results, with 1 % error, have been attained. Copyright© (2006) by the International Measurement Federation (IMEKO).

Guide to best practices for ocean CO2 measurements

CHAP 1 - Introduction to the Guide CHAP 2 - Solution chemistry of carbon dioxide in sea water CHAP 3 - Quality assurance CHAP 4 - Recommended standard operating procedures (SOPs) SOP 1 - Water sampling for the parameters of the oceanic carbon dioxide system SOP 2 - Determination of total dissolved inorganic carbon in sea water SOP 3a - Determination of total alkalinity in sea water using a closed-cell titration SOP 3b - Determination of total alkalinity in sea water using an open-cell titration SOP 4 - Determination of p(CO2) in air that is in equilibrium with a discrete sample of sea water SOP 5 - Determination of p(CO2) in air that is in equilibrium with a continuous stream of sea water SOP 6a - Determination of the pH of sea water using a glass/reference electrode cell SOP 6b - Determination of the pH of sea water using the indicator dye m-cresol purple SOP 7 - Determination of dissolved organic carbon and total dissolved nitrogen in sea water SOP 7 en Español - Determinacion de carbono organico disuelto y nitrogeno total disuelto en agua de mar SOP 11 - Gravimetric calibration of the volume of a gas loop using water SOP 12 - Gravimetric calibration of volume delivered using water SOP 13 - Gravimetric calibration of volume contained using water SOP 14 - Procedure for preparing sodium carbonate solutions for the calibration of coulometric CT measurements SOP 21 - Applying air buoyancy corrections SOP 22 - Preparation of control charts SOP 23 - Statistical techniques used in quality assessment SOP 24 - Calculation of the fugacity of carbon dioxide in the pure gas or in air CHAP 5 - Physical and thermodynamic data Errata - to the hard copy of the Guide to best practices for ocean CO2 measurements

Interaction of echinomycin with guanine: electrochemistry and spectroscopy studies

The interaction of antitumor antibiotic, echinomycin (Echi) with guanine (Gua) was thoroughly investigated by adsorptive transfer stripping cyclic voltammetry, ultraviolet and visible adsorption spectra (UV/Vis) and Fourier-transform infrared spectroscopy (FTIR). Electrochemistry provided a simple tool for verifying the occurrence of interaction between Echi and Gua. Echi could be accumulated from the solution and give well-defined electrochemical signals in 0.1 M phosphate buffer solution (pH 7.0) only when Gua was present on the surface of the electrochemically pretreated glass carbon electrode (GCE), suggesting a strong binding of Echi to Gua. All the acquired spectral data showed that a new adduct between Echi and Gua was formed, and two pairs of adjacent intermolecular hydrogen bonds between the Ala backbone atoms in Echi and Gua (Ala-NH to Gua-N3 and Gua-NH2 to Ala-CO) played a dominating role in the interaction. Electrochemistry coupled with spectroscopy techniques could provide a relatively easy way to obtain useful insights into the molecular mechanism of drug-DNA interactions, which should be important in the development of new anticancer drugs with specific base recognition.

Microperoxidase-11 modified electrode and its electrocatalytic activity on the reduction of O-2 and H2O2

Microperoxidase-11 (MP-11) was immobilized on the surface of a silanized glass carbon electrode by means of the covalent bond with glutaraldehyde. The measurements of cyclic voltammetry demonstrated that the formal redox potential of immobilized MP-11 was -170 mV. which is significantly more positive than that of MP-11 in a solution or immobilized on the surface of electrodes prepared with other methods. This MP-11 modified electrode showed a good electrocatalytic activity and stability for the reduction of oxygen and hydrogen peroxide.

pH Limitations in environmental geochemical monitoring

Senior thesis written for Oceanography 445

On an Electrode Modified by a Supramolecular Ruthenium Mixed Valence (Ru(II)/Ru(III)) Diphosphine-Porphyrin Assembly

Three novel polymetallic ruthenium (III) meso-tetra(4-pyridyl)porphyrins containing peripheral ""RuCl(3)(dppb)"" moieties have been prepared and characterized. The X-ray structure of the tetraruthenated {NiTPyP[RuCl(3)(dppb)](4)} porphyrin complex crystallizes in the triclinic space group FT. This structure is discussed and compared with the crystal data for the mer-[RuCl(3)(dppb)(py)]. The {TPyP[RuCl(3)(dppb)](4)} and {CoTPyP[RuCl(3)(dppb)](4)} porphyrins were used to obtain electrogenerated films on ITO and glass carbon electrode surfaces, respectively. Such tetraruthenated porphyrins form films of a mixed-valence species {TPyP[Ru(dppb)](4)(mu Cl(3))(2)}(2)(4n2+) and {CoTPyP[Ru(dppb)](4)(mu Cl(3))(2)}(2n)(4n2+) on the electrode surface. The modified electrode with {CoTPyP[RuCl(3)(dppb)](4)} is very stable and can be used to detect organic substrates such as catechol.

Stripping voltammetry of mercury(II) with a chemically modified carbon paste electrode containing silica gel functionalized with 2,5-dimercapto-1,3,4-thiadiazole

The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2,5-dimercapto-1,3,4-thiadiazole (DTTPSG-CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range -0.2 to +0.8 V (vs. Ag/AgCl), (0.02 mol L-1 KNO3; nu=20 mV s(-1)) show two peaks one at about 0.0 V and other at 0.31 V. However, the cathodic wave peak, around 0.0 V, is irregular and changes its form in each cycle. This peak at about 0.0 V is the reduction current for mercury(II) accumulated in the DTTPSG-CPE. The anodic wave peak at 0.31 V is well-defined and does not change during the cycles. The resultant material was characterized by cyclic and differential pulse anodic stripping voltammetry performed with the electrode in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. The precision for six determinations (n=6) of 0.05 and 0.20 mg (L)-(1) Hg(II) was 2.8 and 2.2% (relative standard deviation), respectively. The method was satisfactory and used to determine the concentration of mercury(II) in natural waters contaminated by this metal.