Study of the electrochemical reduction of amoebicide Teclozan and its amperometric determination in pharmaceutical formulations

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of Ionic Liquid on the Determination of Aromatic Amines as Contaminants in Hair Dyes by Liquid Chromatography Coupled to Electrochemical Detection

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

Electrochemical reduction and determination of Cibacron Blue F3GA at poly-L-lysine modified glassy carbon electrode

The oxidation of a reactive dye, Cibacron Blue F3GA, CB, (C.I. 61211), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode occurs in two steps at 2.0 < pH < 10 involving one electron transfer each to the amine group leading to the imide derivative. Stable films of poly-L-lysine (PLL) in the presence of glutaraldehyde (GA) 97.5%:2.5% on glassy carbon electrode can be used to detect low levels of dye using its oxidation peak at +0.75V by voltammetry. Linear calibration graphs were obtained for the CB reactive dye, from 1.0 X 10(-6) to 1.0 X 10(-5) mol L-1 in B-R buffer, pH 2.0, using a pre-concentration off-line during 10 min. The detection limit (3 sigma/slope) was calculated to be 4.5 X 10(-8) mol L-1. Films of PLL can readily be applied for the determination of CB dye bearing aminoanthraquinone as chromophore and chlorotriazinyl as reactive group at concentrations at least 100 times lesser than using a glassy carbon electrode without modification. The method described was applied for the determination of CB dye in tap water and raw water collected from the municipal treatment plant with a recovery of 89.2% +/- 5.4 and 88.0% +/- 6.5, respectively. (c) 2005 Elsevier Ltd. All rights reserved.

A disposaable electrochemical sensor for the rapid determination of levodopa

Levodopa (L-dopa), the biological precursor of catecholamines, is the most widely prescribed drug in the treatment of Parkinson's disease. The present work presents a proposal for the application of a gold screen-printed electrode an electrochemical sensor for monitoring L-dopa in stationary solution and a flow system. Using the electrooxidation of L-dopa at +0.63 V in acetate buffer pH 3.0 on a gold screen-printed electrode it is possible to obtain a linear calibration curve from 9.9 x 10(-5) to 1.2 x 10(-3) mol L-1 and a detection limit of 6.8 x 10(-5) mol L-1. Under amperometric conditions (E-app = 0.8 V; flow rate = 14.1 ml, min(-1); pH 3.0), an analytical calibration graph for L-dopa was obtained from 1.0 x 10(-6) mol L-1 6.6 x 10(-4) mol L-1 with a detection limit of 9.9 x 10(-7) mol L-1. The method was successfully applied to the determination of L-dopa in commercial dosage forms without any pre-treatment. (c) 2005 Elsevier B.V. All rights reserved.

Determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with electrochemical detection

The cyclic voltammetric behavior of acetaldehyde and the derivatized product with 2,4-dinitrophenylhydrazine (DNPHi) has been studied at a glassy carbon electrode. This study was used to optimize the best experimental conditions for its determination by high-performance liquid chromatographic (HPLC) separation coupled with electrochemical detection. The acetaldehyde-2,4-dinitrophenyl.hydrazone (ADNPH) was eluted and separated by a reversed-phase column, C-18, under isocratic conditions with the mobile phase containing a binary mixture of methanol/LiCl(aq) at a concentration of 1.0 x 10(-3) M (80:20 v/v) and a flow rate of 1.0 mL min(-1). The optimum condition for the electrochemical detection of ADNPH was +1.0 V vs. Ag/AgCl as a reference electrode. The proposed method was simple, rapid (analysis time 7 min) and sensitive (detection limit 3.80 mu g L-1) at a signal-to-noise ratio of 3:1. It was also highly selective and reproducible [standard deviation 8.2% +/- 0.36 (n = 5)]. The analytical curve of ADNPH was linear over the range of 3-300 mg L-1 per injection (20 mu L), and the analytical recovery was > 99%.

Electrochemical oxidation and voltammetric determination of the antimalaria drug primaquine

Primaquine, an antimalarial drug, presents a well-defined oxidation peak around +0.6V vs SCE at a glassy carbon electrode that can be used for its determination. Calibration graphs were obtained for primaquine in B-R buffer pH 4.0 from 3.00 x 10(-5) mol L-1 to 1.00 x 10(-2) mol L-1 using linear-scan voltammetry and 3.00 x 10(-5) mol L-1 to 1.00 x 10(-2) mol L-1 using differential pulse or square-wave voltammetry. The correspondent detection limits was 9.4 mu g mL(-1); 4.2 and 1.8 mu g mL(-1), respectively. All the voltammetric methods were applied with success in direct determination of the primaquine in commercial tablets without separation or extraction procedures.

Determination of aldehydes and ketones in fuel ethanol by high-performance liquid chromatography with electrochemical detection

A new methodology was developed for analysis of aldehydes and ketones in fuel ethanol by high-performance liquid chromatography (HPLC) coupled to electrochemical detection. The electrochemical oxidation of 5-hydroxymetkylfurfural, 2-furfuraldehyde, butyraldehyde, acetone and methyl ethyl ketone derivatized with 2,4-dinitrophenylhydrazine (DNPH) at glassy carbon electrode present a well defined wave at +0.94 V; +0.99 V; +1.29 V; +1.15 V and +1.18 V, respectively which are the basis for its determination on electrochemical defector. The carbonyl compounds derivatized were separated by a reverse-phase column under isocratic conditions with a mobile phase containing a binary mixture of methanol /LiClO4(aq) at a concentration of 1.0 x 10(-3) mol L-1 (80:20 v/v) and a flow-rate of 1.1 mL min(-1). The optimum potential for the electrochemical detection of aldehydes-DNPH and ketones-DNPH was +1.0 V vs. Ag/AgCl. The analytical curve of aldehydes-DNPH and ketones-DNPH presented linearity over the range 5.0 to 400.0 ng mL(-1), with detection limits of 1.7 to 2.0 ng mL(-1) and quantification limits from 5.0 to 6.2 ng mL(-1), using injection volume of 20 mu L. The proposed methodology was simple, low time-consuming (15 min/analysis) and presented analytical recovery higher than 95%.

Construction and application of an electrochemical sensor for paracetamol determination based on iron tetrapyridinoporphyrazine as a biomimetic catalyst of P450 enzyme

This work describes the construction and application of a biomimetic sensor for paracetamol determination in different samples. The sensor was prepared by modifying a glassy carbon electrode surface with a Nafion (R) membrane doped with FeTPyPz. The best performance of the sensor in 0.1 mol L-1 acetate buffer was at pH 3.6. Under these conditions, an oxidation potential of paracetamol was observed at 445 mV vs. Ag vertical bar AgCl. The sensor presented a linear response range between 4.0 and 420 mu mol L-1, a sensitivity of 46.015 mA L mol(-1) cm(-2), quantification and detection limits of 4.0 mu mol L-1 and 1.2 mu mol L-1, respectively. A detailed investigation about its electrochemical behavior and selectivity was carried out. The results suggested that FeTPyPz presents catalytic properties similar to P450 enzyme for paracetamol oxidation. Finally, the sensor was applied for paracetamol determination in commercial drugs and for the monitoring of its degradation in an electrochemical batch reactor effluent.

A New Indirect Electrochemical Method for Determination of Ozone in Water Using Multiwalled Carbon Nanotubes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrochemical sensor highly selective for estradiol valerate determination based on a modified carbon paste with iron tetrapyridinoporphyrazine

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spectrophotometric determination of manganese in steels by on-line electrochemical oxidation

The aim of this work is to propose a flow spectrophotometric procedure for manganese determination in steel based on electrochemical oxidation of Mn(II) to Mn(VII) at a Pt electrode surface by means of the catalytic effect of Ag(I). The on-line oxidation step was obtained by injecting sample and electrolyte solution directly into an electrolytic cell. After electrolysis, the injectate was homogenized by bubbling air. The permanganate ions produced were passed through the spectrophotometer where absorbance was monitored at 545 nm. Effects of direct current, silver concentration, timing, flow rates, concentration and composition of support electrolyte were investigated. Direct current and silver content manifested themselves as the most relevant parameters. For determination of manganese in the 5.00 - 150 mg L -1 range (r=0,9998) and 60 s electrolysis time, the sample throughput was 20 h -1. Accuracy was assessed by analyzing ten steel standard reference materials. Results are precise (R.S.D. <3%) and in agreement with certified values of reference materials and with standard methods at 95% confidence level.

Determination of the phthalocyanine textile dye, reactive turquoise blue, by electrochemical techniques

Turquoise blue 15 (AT15) is a reactive dye widely used in the textile industry to color natural fibers. The presence of these dyes in effluent and industrial wastewater is of considerable interest due ecotoxicological and environmental problems. The electrochemical reduction of this dye has been investigated in aqueous solution using cyclic voltammetry, controlled potential electrolysis and cathodic stripping voltammetry. Optimum conditions for dye discoloration by controlled potential electrolysis use an alkaline medium. Using cathodic stripping voltammetry a linear calibration graph was obtained from 5.00×10-8 mol L-1 to 1.00×10 -6 mol L-1 of AT15 at pH 4.0, using accumulation times of 180 and 240 s and an accumulation potential of 0.0 V. The proposed method was applied in direct determination of the dye in tap water and in textile industry effluent.

Study of electrochemical oxidation and determination of albendazole using a glassy carbon-rotating disk electrode

In this work, electrochemical oxidation of albendazole (ABZ) was carried out using a glassy carbon-rotating disk electrode. Development of electroanalytical methodology for ABZ quantification in pharmaceutical formulations was also proposed by using linear sweep voltammetric technique. Electrochemical oxidation is observed for ABZ at E 1/2 = 0.99:V vs. Ag/AgCl sat, when an anodic wave is observed. Kinetic parameters obtained for ABZ oxidation exhibited a standard heterogeneous rate constant for the electrodic process equal to (1.51 ± 0.07) ± 10 -5:cm:s -1, with a αn a value equal to 0.76. Limiting current dependence against ABZ concentration exhibited linearity on 5.0 ± 10 -5 to 1.0 ± 10 -2:mol:l -1 range, being obtained a detection limit of 2.4 ± 10 -5:mol:l -1. Proposed methodology was applied to ABZ quantification in pharmaceutical formulations. © 2005 Elsevier SAS. All rights reserved.

Electrochemical reduction and voltammetric determination of diloxanide furoate in non-aqueous medium

The electrochemical reduction of diloxanide furoate (DF) in acetonitrile on glassy carbon electrode was studied in this work. It was observed that DF is reduced after a reversible one-electron transfer followed by an irreversible chemical reaction, diagnosed as C-Cl bond cleavage. Its reduction was followed by linear (LSV), differential pulse (DPV) and square wave voltammetry (SWV). Analytical curves were obtained for DF determination using all the investigated voltammetric techniques. For LSV was obtained a linear range (LR) from 5.0 × 10-4 to 1.0 × 10-2 mol L-1, with detection limit (DL) of 1.5 × 10-4 mol L-1 and sensitivity (S) of 2.1 × 104 μA mol-1 L. The analytical parameters obtained by DPV were: LR = 5.0 × 10-4 to 2.2 × 10-3 mol L-1, DL = 7.8 × 10-5 mol L-1, S = 3.7 × 104 μA mol-1 L. For SWV were obtained a LR = 7.5 × 10-6 to 1.2 × 10 -3 mol L-1, DL = 5.5 × 10-6 mol L -1 and S = 2.8 × 105 μA mol-1 L. Thus, the SWV was the most sensible technique, which can be used for DF determination at low concentration levels. Statistics methods were used to evaluate the analytical procedure, where recovery around to 100% was obtained for all voltammetric techniques. Relative standard deviations were lower than 5.0% (N=5). The obtained t values evaluating all the three voltammetric methods were less than the tabulated ones, indicating that there are no evidences of systematic error. ©2005 Sociedade Brasileira de Química.

Electrochemical behavior and voltammetric determination of pyrazinamide using a poly-histidine modified electrode

Pyrazinamide (Pyrazinecarboxamide-PZA) is a drug that is used to treatment tuberculosis. In the present work, the voltammetric behavior of PZA was studied using a screen-printed modified electrode (SPCE). The modified electrode was constructed using poly-histidine films, and it showed an electrocatalytic effect, thus promoting a decrease in PZA reduction potential and improving the voltammetric response. Cyclic voltammetry and electrochemical impedance spectroscopy techniques have been employed in order to elucidate of the electrodic reaction. The results allowed the proposal that in the PZA reduction, a further chemical reaction occurs that corresponds to a second-order process which is subsequent to the electrode reaction. In addition, a sensitive voltammetric method was developed, and it was successfully applied for PZA determination in human urine samples. The best response was found using SPCE modified with poly-histidine prepared by histidine monomer electropolymerization (SPCE/EPH). The electroanalytical performance of the SPCE/EPH was investigated by linear sweep (LSV), differential pulse (DPV), and square wave voltammetry (SWV). A linear relationship between peak current and PZA concentrations was obtained from 9.0 × 10-7 to 1.0 × 10-4 mol L-1 by using DPV. The limit of detection at 5.7 × 10 -7 mol L-1 was estimated, and a relative standard deviation of the 5.0 × 10-6 mol L-1 of PZA of 10 measurement was 3.7%. © 2012 Elsevier B.V. All rights reserved.