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ABSTRACT: In this study, a novel method was proposed for the selective determination of tryptophan (TRP) in blood serum in the presence of tyrosine. This method is based on the electrochemical reduction of 2-amino-3-(5-oxo-3,5-dihydro-2H-indol-3-yl)-propionic acid (5-O-3,5DH-TRP) formed by the oxidation of TRP on the electrochemically treated pencil graphite (ETPG) electrode surface at a suitable potential value. The parameters affecting the TRP determination were deeply investigated. The optimal pH value was determined as 3. The highest reduction current intensity was obtained at the accumulation potential and time values of +0.95 V and 120 s, respectively. The reduction peak current values of 5-O-3,5DH-TRP versus TRP concentration at the ETPG electrode showed linearity in the range from 0.5 μM to 50.0 μM (R(2)=0.9962) with a detection limit of 0.05 μM (S/N=3). The reduction peak intensity of 5-O-3,5DH-TRP on the ETPG electrode showed no significant change in the presence of different interfering substances. The analytical application of the proposed novel method was successfully tested by using human blood serum samples.
Biosensors & bioelectronics 10/2011; 31(1):26-31. · 5.43 Impact Factor
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ABSTRACT: The removal of Clopyralid (CLPYD) from aqueous solutions was performed by the electro-Fenton process in which hydroxyl radicals are produced electrocatalytically and used to degrade the persistent organic pollutants. The decay kinetics well fitted to pseudo-first order reaction and absolute rate constant of the oxidation reaction of CLPYD was determined as (4.4 ± 0.2) × 108 M–1 s–1. The oxidation intermediates of CLPYD were identified by HPLC and IC analysis. Based on these intermediates, a general oxidation mechanism was proposed in acid medium. Mineralisation ability of the system was followed by the chemical oxygen demand (COD) analysis. The obtained results showed that the CLPYD aqueous solutions were efficiently mineralised during the electro-Fenton treatment.
Intern. J. Environ. Anal. Chem. 03/2010; 90(Nos. 3–6):478-486.
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ABSTRACT: Preparation of electrochemically treated pencil graphite (ETPG) electrode and its application for the determination of DA in the presence of ascorbic (AA) and uric (UA) acids were investigated. Several important parameters were worked to control the performance of the ETPG electrode which showed a high selectivity and sensitivity toward DA. A linear relationship was obtained for dopamine (DA) over the concentration range of 0.01 and 5.0 μM with a detection limit of 0.31 nM in the presence of AA and UA. The fabrication reproducibility of the ETPG electrodes (n=10) showed an acceptable reproducibility with a RSD of 2.0% for 5.0 μM DA. The determination of DA in blood serum without any pretreatment and dilution has been reported for the first time in this work.
Electroanalysis 09/2009; 21(21):2363 - 2370. · 2.87 Impact Factor
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ABSTRACT: Preparation of a polypyrrole nanofiber (PPyNF) modified pencil graphite (PG) electrode and its usage in the electrochemical DNA biosensors was investigated. The electrodes (PPyNF/PG1 and PPyNF/PG2) were prepared from a solution containing 0.1 M pyrrole, 0.1 M Na2CO3 and 0.1 M LiCIO4 by using potentiostatic and potentiodynamic methods. PPyNF/PG2 electrodes which were prepared by potentiostatic procedure showed higher responses for the oxidation of ds-DNA than the PPyNF/PG1 electrodes prepared by potentiodynamic methods. Immobilization of the ds-DNA on PG and PPyNF/PG surfaces was performed at a constant potential, +0.5 V, for 300 s in 0.5 M ABS (pH 4.8) containing 15 μg mL−1 ds-DNA and 20 mM LiCIO4. The oxidation peak potentials of the ds-DNA bases, guanine and adenine, were shifted to more cathodic values by using PPyNF/PG electrodes. The oxidation signal of the guanine base of ds-DNA was decreased in the presence of methylene blue.
Electroanalysis 09/2007; 19(21):2208 - 2216. · 2.87 Impact Factor
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ABSTRACT: Electro-Fenton process has been widely used in the treatment of organic pollutants lately. Its oxidation efficiency mainly depends on the electrode materials. In this study, boron doped diamond (BDD), carbon sponge (CS) and platinum (Pt) electrodes were used at four different configurations as anode and cathode. The oxidation efficiencies of BDD anode and CS cathode were investigated together for the first time in the electro-Fenton process. Propham was used as the model pollutant. The obtained results indicate that the decay rate of propham and the mineralization rate of propham aqueous solutions were highest in the case of BDD and CS electrodes as expected. The obtained mineralization current efficiency (MCE) value was 81% at 100 mA in the presence of 0.2 mM Fe3+ for 30 min electrolysis. The oxidative degradation intermediates of propham showed different accumulation characteristics in all configurations. The oxamic acid resisted to mineralization but it rapidly degraded in the presence of BDD anode.
Applied Catalysis B: Environmental. 89:620-626.
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ABSTRACT: This study aims the removal of a carbamate herbicide, propham, from aqueous solution by direct electrochemical advanced oxidation process using a boron-doped diamond (BDD) anode. This electrode produces large quantities of hydroxyl radicals from oxidation of water, which leads to the oxidative degradation of propham up to its total mineralization. Effect of operational parameters such as current, temperature, pH and supporting electrolyte on the degradation and mineralization rate was studied. The applied current and temperature exert a prominent effect on the total organic carbon (TOC) removal rate of the solutions. The mineralization of propham can be performed at any pH value between 3 and 11 without any loss in oxidation efficiency. The propham decay and its overall mineralization reaction follows a pseudo-first-order kinetics. The apparent rate constant value of propham oxidation was determined as 4.8×10−4 s−1 at 100 mA and 35 °C in the presence of 50 mM Na2SO4 in acidic media (pH: 3). A general mineralization sequence was proposed considering the identified oxidation intermediates.
Water Research.
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ABSTRACT: The degradation of the picloram, a widely used herbicide, has been undertaken by the electrochemical advanced oxidation process, namely electro-Fenton in aqueous solution. This process generates catalytically hydroxyl radicals that are strong oxidizing reagents for the oxidation of organic substances. Degradation kinetics of picloram was investigated. Kinetic results evidence a pseudo first-order degradation, with a rate constant of reaction between picloram and hydroxyl radicals of (2.73 ± 0.08) × 109 M−1 s−1. The effect of applied current and catalyst concentration on the degradation and mineralization of picloram was also investigated. The optimum applied current and catalyst concentration values for the degradation of picloram was determined as 300 mA and 0.2 mM Fe3+, respectively. Mineralization of picloram was followed by the total organic carbon (TOC) analysis. At the end of 8 h of electrolysis, 95% of the initial TOC was removed. Several degradation products were identified by using HPLC, LC–MS, GC–MS, and IC analysis. The identified by-products allowed to propose a mineralization pathway for the picloram degradation.
Journal of Hazardous Materials.
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ABSTRACT: The removal of a carbamate herbicide, propham, from aqueous solution has been carried out by the electro-Fenton process. Hydroxyl radical, a strong oxidizing agent, was generated catalytically and used for the oxidation of propham aqueous solutions. The degradation kinetics of propham evidenced a pseudo-first order degradation. The absolute rate constant of second order reaction kinetics between propham and OH was determined as (2.2 ± 0.10) × 109 m−1 s−1. The mineralization of propham was followed by the organic carbon (TOC) removal. The optimal Fe3+ concentration was found as 0.5 mM at 300 mA. The 94% of initial TOC of 0.25 mM propham solution was removed in 8 h at the optimal conditions by using the cathode area to solution volume ratio of 3.33 dm−1. The maximum mineralization current efficiency values were obtained at 60 mA in the presence of 0.5 mM Fe3+. During the electro-Fenton treatment, several degradation products were formed. These intermediates were identified by using high performance liquid chromatography, liquid chromatography–mass spectrometry, gas chromatography–mass spectrometry and ion chromatography analysis. The identified by-products allowed proposing a pathway for the propham mineralization.
Chemosphere.
