Electrochemical reduction of nitroprusside on a glassy carbon electrode modified by poly-L-lysine films

The present work describes the preparation and characterization of polyelectrolyte coatings of poly-L-lysine (PLL) to modify a glassy carbon electrode and its application to the pre-accumulation of nitroprusside (NP). The effects of the coating on the electrochemical reduction of NP were investigated. The performance of the modified electrode indicates that the drug can be immobilized by electrostatic interaction and the voltammetric signal monitored at all pH values in the range of 2-12. The strong interaction between NP and PLL stabilizes the complex on the electrode surface and minimizes the chemical reaction of lost CN- ions as a subsequent reaction of electron transfer, which could improve the action mechanism of NP.

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.

Study of the Electrochemical Behavior of Histamine Using a Nafion (R)-Copper(II) Hexacyanoferrate Film-Modified Electrode.

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

Potentiometric study using chemically modified silica gel with pyridinium as membrane for ClO4 - ions

A potentiometric sensor for the perchlorate anion was developed by mixing chemically modified silicagel with pyridinium perchlorate, with an epoxy polymer and graphite. The electrode showed Nernstian response between 1.0 × 10-2 and 1.0 × 10-3M perchlorate concentrations. The electrode showed high selectivity to this ion at solutions pH between 5.5 and 8.0. The presence of IO4 -, NO3 -,Br-, IO3 -, Cl- and SO4 2- ions in the solutions, had only small interference in the electrode response in the range mentioned. © 1995 Springer-Verlag.

Study of the electrochemical behavior of histamine using a Nafion®-copper (II) hexacyanoferrate film-modified electrode

A study on the electrochemical behavior of histamine species in aqueous medium is described. A glassy carbon electrode chemically modified with copper (II) hexacyanoferrate (CuHCFe) film and covered with Nafion® film was employed. The interaction between the analyte and the CuHCFe film can be demonstrated by a decrease in both the cathodic and anodic peak currents at 0.68V (vs. Ag/AgCl), attributed to the film and the appearance of new peak current at 0.47V. Cyclic voltammetric parameters obtained for histamine indicate the formation of stable complex between histamine adsorbed at the electrode surface. The dependence of peak currents on the concentration of the analyte is not linear in the employed work range, indicating the presence of a coupled chemical reaction in the electrodic process. © 2010 by ESG.

A new hybrid polyhedral cubic silsesquioxane chemically modified with 4-amino-5-(4-pyridyl)-4H-1,2,4-triazole-3-thiol (APTT) and copper hexacyanoferrate(III) for voltammetric determination of nitrite

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

Simple and direct potentiometric determination of potassium ions in biodiesel microemulsions at a glassy carbon electrode modified with nickel(II) hexacyanoferrate nanoparticles

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

Voltammetric Behavior of a Chemically Modified Silsesquioxane with 4-Amino-5-Phenyl-4h-[1,2,4]-Triazole-3-Thiol and its Application for Detection of L-Dopamine

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

Determination of furanic aldehydes in sugarcane bagasse by high-performance liquid chromatography with pulsed amperometric detection using a modified electrode with nickel nanoparticles

A glassy carbon electrode chemically modified with nickel nanoparticles coupled with reversed-phase chromatography with pulsed amperometric detection was used for the quantitative analysis of furanic aldehydes in a real sample of sugarcane bagasse hydrolysate. Chromatographic separation was carried out in isocratic conditions (acetonitrile/water, 1:9) with a flow rate of 1.0 mL/min, a detection potential of -50 mV vs. Pd, and the process was completed within 4 min. The analytical curves presented limits of detection of 4.0 × 10(-7) mol/L and 4.3 × 10(-7) mol/L, limits of quantification of 1.3 × 10(-6) and 1.4 × 10(-6) mol/L, amperometric sensitivities of 2.2 × 10(6) nA mol/L and 2.7 × 10(6) nA mol/L for furfural and 5-hydroxymethylfurfural, respectively. The values obtained in this sample by the standard addition method were 1.54 ± 0.02 g/kg for 5-hydroxymethylfurfural and 11.5 ± 0.2 g/kg for furfural. The results demonstrate that this new proposed method can be used for the quick detection of furanic aldehydes without the interference of other electroactive species, besides having other remarkable merits that include excellent peak resolution, analytical repeatability, sensitivity, and accuracy.

Is the poly (methylene blue)-modified glassy carbon electrode an adequate electrode for the simple detection of thiols and amino acid-based molecules?

This paper describes the preparation, characterization, and use of poly (methylene blue) (PMB)-modified glassy carbon electrodes (GCE) (GCE-PMB) in the detection of the thiols L-cysteine (L-CySH) and N-acetyl cysteine (Acy), and the herbicide glyphosate (GLYP) in pH 5.3 aqueous solution. The polymer film prepared by electropolymerization showed different characteristics such as robustness, stability, and redox properties satisfactorily. The surface coverage concentration (Gamma) of PMB was found to be 7.90 x 10(-9) - mol cm(-2). Moreover, we observed strong adhesion of the polymer film to the electrode surface. The results using GCE-PMB as a sensor indicated that this modified electrode exhibited electrocatalytic activity toward the detection of thiols and glyphosate in 0.1 mol L-1 KO (pH 5.3). Meanwhile, strong adsorption of the analytes on the GCE-PMB electrodes was also observed. Otherwise, using a low concentration (1 x 10(-4) mol L-1) of L-cysteine and N-acetyl cysteine and 8.9 x 10(-6) mol L-1 of glyphosate, separately, it was possible to observe a well-defined electrochemical response, thus providing an opportunity to further understand the applicability of PMB as a sensor for amino acid-based molecules. (C) 2012 Elsevier B.V. All rights reserved.

Detection of exocytosis at individual pancreatic beta cells by amperometry at a chemically modified microelectrode.

Amperometry at a carbon fiber microelectrode modified with a composite of ruthenium oxide and cyanoruthenate was used to monitor chemical secretions of single pancreatic beta cells from rats and humans. When the insulin secretagogues glucose, tolbutamide, and K+ were applied to the cell, a series of randomly occurring current spikes was observed. The current spikes were shown to be due to the detection of chemical substances secreted from the cell. Chromatography showed that the primary secreted substance detected by the electrode was insulin. The current spikes were strongly dependent on external Ca2+, had an average area that was independent of the stimulation method, and had an area distribution which corresponded to the distribution of vesicle sizes in beta cells. It was concluded that the spikes were due to the detection of concentration pulses of insulin secreted by exocytosis.

Charge carrier exchange at chemically modified graphene edges: A density functional theory study

Heteroatom doping on the edge of graphene may serve as an effective way to tune chemical activity of carbon-based electrodes with respect to charge carrier transfer in an aqueous environment. In a step towards developing mechanistic understanding of this phenomenon, we explore herein mechanisms of proton transfer from aqueous solution to pristine and doped graphene edges utilizing density functional theory. Atomic B-, N-, and O- doped edges as well as the native graphene are examined, displaying varying proton affinities and effective interaction ranges with the H3O+ charge carrier. Our study shows that the doped edges characterized by more dispersive orbitals, namely boron and nitrogen, demonstrate more energetically favourable charge carrier exchange compared with oxygen, which features more localized orbitals. Extended calculations are carried out to examine proton transfer from the hydronium ion in the presence of explicit water, with results indicating that the basic mechanistic features of the simpler model are unchanged.

Chemically modified ribbon edge stimulated H2 dissociation: A first-principles computational study

First-principles computational studies indicate that (B, N, or O)-doped graphene ribbon edges can substantially reduce the energy barrier for H2 dissociative adsorption. The low barrier is competitive with many widely used metal or metal oxide catalysts. This suggests that suitably functionalized graphene architectures are promising metal-free alternatives for low-cost catalytic processes.

Nano-confined synthesis of highly ordered mesoporous carbon and its performance as electrode material for electrochemical behavior of riboflavin (vitamin B2) and dopamine

Highly ordered mesoporous carbon (MC) has been synthesized from sucrose, a non-toxic and costeffective source of carbon. X-ray diffraction, N2 adsorption–desorption isotherm and transmission electron micrograph (TEM) were used to characterize the MC. The XRD patterns show the formation of highly ordered mesoporous structures of SBA15 and mesoporous carbon. The N2 adsorptiondesorption isotherms suggest that the MC exhibits a narrow pore-size distribution with high surface area of 1559 m2/g. The potential application of MC as a novel electrode material was investigated using cyclic voltammetry for riboflavin (vitamin B2) and dopamine. MC-modified glassy carbon electrode (MC/GC) shows increase in peak current compared to GC electrode in potassium ferricyanide which clearly suggest that MC/GC possesses larger electrode area (1.8 fold) compared with bare GC electrode. The electrocatalytic behavior of MC/GC was investigated towards the oxidation of riboflavin (vitamin B2) and dopamine using cyclic voltammetry which show larger oxidation current compared to unmodified electrode and thus MC/GC may have the potential to be used as a chemically modified electrode.

Iminodiacetic acid functionalized polypyrrole modified electrode as Pb(II) sensor: Synthesis and DPASV studies

An electrochemical lead ion sensor has been developed by modification of carbon paste electrode (CPE) using polypyrrole functionalized with iminodiacetic acid (IDA-PPy) containing carboxyl group. The electrochemical response of Pb2+ ion on the IDA-PPy modified CPE has been evaluated and the controling parameters have been optimized using differential pulse anodic stripping voltammetry (DPASV). The IDA-PPy modified CPE shows a linear correlation for Pb2+ concentrations in the range of 1 x 10(-6) to 5 x 10(-9) M and the lower detection limit of Pb2+ has been found to be 9.6 x 10(-9) M concentration. Other tested metal ions, namely Cu2+, Cd2+, Co2+, Hg2+, Ni2+ and Zn2+, do not exhibit any voltammetric stripping response below 1 x 10(-7) M concentration. However, the Pb2+ response is affected in the presence of molar equivalents or higher concentrations of Cu2+, Cd2+ and Co2+ ions in binary systems with Pb2+, consequent to their ability to bind with iminodiacetic acid, while Hg2+, Ni2+ and Zn2+ do not interfere at all. A good correlation has been observed between the lead concentrations as analyzed by DPASV using IDA-PPy modified CPE and atomic absorption spectrophotometry for a lead containing industrial effluent sample. (C) 2014 Elsevier Ltd. All rights reserved.