Estudo voltamétrico do complexo de cobre(II) com o ligante vermelho de alizarina S, adsorvido na superfície do eletrodo de grafite pirolítico Voltammetric study of complex of copper (II) with alizarin red S ligand, absorbed on surface of pyrolytic graphite electrode

<abstract language="eng">The alizarin red S (ARS) has been used as a spectrophotometric reagent of several metals for a long time. Now this alizarin has been used as modifier agent of electrodes, for voltammetric analyses. In this work cyclic voltammetry experiments was accomplished on closed circuit, with the objective of studying the voltammetric behavior of alizarin red S adsorbed and of its copper complex, on the surface of the pyrolytic graphite electrode. These studies showed that ARS strongly adsorbs on the surface of this electrode. This adsorption was used to immobilize ions copper(II) from the solution

Graphite electrodes modified by 8-hydroxyquinolines and its application for the determination of copper in trace levels

Surface modification by 8-hydroxyquinoline-5-sulfonic acid (8-HQS) or 8-hydroxyquinoline (8-HQ) on a graphite electrode through irreversible adsorption is reported in this paper. Cyclic voltammetry was used to characterize the surface behavior. The modified surface exhibited an affinity to chelating Cu(II) in the solution, forming a Cu(II) complex, which was employed for Cu(II) trace analysis. Of the metals Zn, Ni, Pb, Co, and Cd, none presented interference until excess concentration of 10 times. Significant interference could be observed from Co(II), Cd(II) and Fe(II) for an excess concentration of 100 times on the analyte. A differential pulse voltammetry, combined with a preconcentrating-stripping process and a standard addition method was used for the analysis. A detection limit for trace copper determination in water, such as 5.1<FONT FACE=Symbol></FONT>10-9 mol L-1, was obtained

Electrochemical Behavior of Ruthenium-Hexacyanoferrate Modified Glassy Carbon Electrode and Catalytic Activity towards Ethanol Electrooxidation

Ruthenium-based hexacyanoferrate (RuHCF) thin film modified glassy carbon electrode was prepared by drop evaporation method. The RuHCF modified electrode exhibited four redox couples in strong acidic solution (pH 1.5) attributed to Fe(CN)6 3- ion and three ruthenium forms (Ru(II), Ru(III) and Ru(IV)), characteristic of ruthenium oxide compounds. The modified electrode displayed excellent electrocatalytic activity towards ethanol oxidation in the potential region where electrochemical processes Ru(III)-O-Ru(IV) and Ru(IV)-O-Ru(VI) occur. Impedance spectroscopy data indicated that the charge transfer resistance decreased with the increase of the applied potential and ethanol concentration, indicating the use of the RuHCF modified electrode as an ethanol sensor. Under optimized conditions, the sensor responded linearly and rapidly to ethanol concentration between 0.03 and 0.4 mol L-1 with a limit of detection of 0.76 mmol L-1, suggesting an adequate sensitivity in ethanol analyses. Printed in Brazil - ©2013 Sociedade Brasileira de Química

Development of a Novel and Simple Electroanalytical Procedure for the Determination of Copper in Biofuel Employing a Sensor Based on Vulcan Functionalized with Carbazone

<div><p>A novel and simple electroanalytical method for the determination of Cu2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH4)2SO4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu2+ concentrations in the range from 6 to 190 nmol L-1 (r = 0.998), with a detection limit of 1.2 nmol L-1. The sensor was successfully applied for the determination of Cu2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method.</p></div

Simple voltammetric determination of iron in ethanol and biodiesel using a bismuth film coated glassy carbon electrode

Square-wave adsorptive stripping voltammetry (SWAdSV) was used to determine iron in ethanol and biodiesel using a bismuth-film electrode (BiFE) prepared onto the surface of a glassy carbon electrode (GCE) by electrochemical deposition to promote the reduction of Fe (III) previously complexed with 1-(2-pyridylazo)-2-naphthol (PAN) directly in the electrochemical cell. The supporting electrolyte was composed by mixture of acetate buffer (0.1 mol L−1, pH 4.5) and ethanol (40/60% v/v) into which 500 µL of a 0.1 mmol L−1 stock solution of PAN was added as complexing agent. The Fe (III)-PAN complex presented a well-defined current peak at −0.7 V. For biodiesel, a treatment with tetramethylammonium hydroxide (TMAH) was proposed as an efficient mean to minimized matrix interferences. A limit of detection of 6.0 × 10−8 mol L−1 (0.06 µmol L−1) and limit of quantification of 2.0 × 10−7 mol L−1 (0.2 µmol L−1) were obtained for Fe(III). Under the optimized conditions, there were no significant interferences from Cu(II), Al(III), Mn(II), Cr(III), Cd(II), Zn(II) and Ni(II) and Pb(II) while Ni(II) interfered significantly. The analytical curves produced linear responses with equations I (µA) = (-1.315 × 10−7 ± 5.158 × 10−8) + (-0.238 ± 0.01) [Fe (III)] (µmol L−1), R2 = 0.992 and I (µA) = (-6.836 × 10−7 ± 1.124 × 10−8) + (-0.408 ± 0.013) [Fe (III)] (µmol L−1), R2=0.998 for pure ethanol and biodiesel, respectively. The method produced satisfactory results in quantifying original quantities of Fe(III) in fuel ethanol (5.65 ± 0.71 µmol L−1) and biodiesel (1.28 ± 0.25 µmol L−1) at a 95% confidence limit (n = 3)