Analytical & Bioanalytical Electrochemistry
Volume:5 Issue: 6, Dec 2013

In the present work, mercury thin film modified carbon microelectrodes were tested towards detection of the pharmacological compounds acemetacin and indomethacin. The compounds were characterized electrochemically by adsorptive stripping differential pulse and square wave voltammetry (AdSDPV and AdSSWV). Best results were obtained via AdSDPV for both compounds (Acemetacin: LOD=1.05×10-7 M, LOQ=3.51×10-7 M; Indomethacin: LOD=1.34×10-7 M, LOQ=4.47×10-7 M). These results are comparable to earlier reports using classical hanging drop mercury electrodes, but with environmental advantages due to the limited mercury amount that is used and the easy way to recover it. Detection and quantification limits are lower than the obtained with currently used analytical techniques.

Double Potential Step Chronoamperometry (DPSC) was used to determine the rate constants for the homogeneous reactions of alcohols with the superoxide ion (O2-) at different temperatures in two room temperature ionic liquids (RTILs). The technique was first tested by determining the pseudo first order rate constant for reduction of azobenzene to hydroazobenzene that, in turn, undergoes the benzidine rearrangement. Our results were in good agreement with values reported in the literature using DPSC and conventional kinetic methods. The activation energy for the oxidation of benzyl alcohol is 19.1 kJ/mol in [bmim][HFP]; which is in good agreement with the value reported in the literature. The corresponding values of S, H and G  for the reaction of superoxide ion with benzhydrol in [bdmim][HFP] calculated at T=45C are –0.49 kJ/mole, 22.4 kJ/mole, and 177.9 kJ/mole, respectively. The second order rate constant for the oxidation of benzyl alcohol at 10C in RTIL in [bmim][HFP] was determined to be 1.3 L mol-1 s-1. The pseudo first order rate constant for the homogeneous reaction of O2 with different primary and secondary alcohols in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][HFP]) and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][HFP] at different temperatures was measured. The pseudo first order rate constant for the reaction of O2- with benzhydrol in [bdmim][HFP] at T= 49, 57, 65, 84 C were found to be 60, 72, 92, 148 L mol-1 s-1. The pseudo first order rate constant for the reaction of O2- with benzhydrol in [bmim][HFP] at T=27, 40 and 80 C were found to be 53,74, 201 L mol-1 s-1.The Arrhenius plot was then used to determine the activation energy and pre-exponential factor for the corresponding reactions.

This study presents a comparative investigation of two dimensionally stable anodes (DSA®) of nominal composition Ti/Ru0.3Ti0.7O2 and Ti/Ir0.3Ti0.7O2, prepared by thermal decomposition at high temperature. The materials were studied by scanning electron microscopy (SEM), cyclic voltammetry and Tafel measurements to obtain informations about their surface and electrocatalytic properties towards O2 evolution reaction. The stability of the samples was investigated under accelerated conditions. It has been observed that the coating surface with 30% mole IrO2 possesses more rough structure with less cracks. Furthermore, it had excellent electrocatalytic activity for the oxygen evolution. Accelerated stability tests showed long lifetime for Ti/Ir0.3Ti0.7O2 electrode. On the other hand, besides the excellent improvement of catalytic activity, the stability of the Ir containing electrode increases compared to the Ru containing one.

The [xCuI:(1-x)Ag2CdI4] fast ionic conductors with various compositions corresponding to x=0.2, 0.4, 0.6 and 0.8 mol. wt % have been prepared by solid state reaction. The fast ionic conductors are characterized by X-ray powder diffraction, FTIR, DTA, DSC, TGA studies. The transmittance spectra of the fast ionic conductors [xCuI:(1-x)Ag2CdI4] (x=0.2, 0.4, 0.6 and 0.8 mol. wt. %) have been measured in the mid-infrared range to investigate the structure of the cadmium iodate anion [(CdI4)2-] matrix and the nature of sites hosting the charge carrier copper ions. X-ray powder diffraction, DTA, DSC, TGA studies was also carried out for confirming doping effect in the formation of composite in which the interface layer plays an important role in controlling the bulk properties of the material.

Abstract-Stable superoxide ion O2- is electrochemically generated in five room temperature ionic liquids namely 1-hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim] [btfmsi], 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [bdmim] [btfmsi], N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [N-Bu-N-MePyrr] [btfmsi], 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [bdmim] [BF4]. Cyclic voltammetry studies were used to check for the short-term stability of O2- in these RTIL’s. In the absence of impurities, especially water, the O2- is stable in these three RTIL’s in the timescale of the cyclic voltammetry. The formal potential for the O2/ O2- couple is found to be -0.86 V vs. Ag/AgCl reference electrode. Hydrophobicity, Viscosity, Oxygen Solubility and Electrical Conductivity were found to be key parameters in the generation of stable superoxide ions in RTILs.

Silver oxyfluoride modified silver electrode was prepared and used to electrocatalytic oxidation of methanol. Fluoride can form a complex with silver ion, and thus be used to modify a silver electrode surface. The electrocatalytic activity of the modified electrode for the oxidation of methanol, in aqueous basic solution was studied by using cyclic voltammetry. Results showed that, silver oxyfluoride modified electrode can improve the activity of Ag towards the oxidation of this small organic molecule. The exchange current density (j0) were 20.37, 10.38 and 1.61 folds higher than for that of bare silver electrode respectively for silver oxyfluoride, silver oxychloride and silver oxybromide modified silver electrodes.The modified electrode showed a stable and linear response in the concentration range of 5×10-3 to 5×10-2 mol L-1 with a correlation coefficient of 0.9953. For silver oxyfluoride modified silver electrode, the transfer coefficient (α), the number of electrons involved in the rate-determining step (nα) and the catalytic rate constant (k) for modified electrode were calculated as 0.45,1 and1.113×105 cm3 mol–1 s–1 respectively.

Nickel bearing compounds exhibit excellent electrochemical properties in an alkaline medium due to the reversible one-electron redox process of the couple Ni(III)/Ni(II). Nickel(II) ions were investigated in the compounds like nickel chloride and nickel sulfate at carbon paste electrode by using cyclic voltammetric technique. The well-defined redox peaks were observed for both nickel chloride and nickel sulfate compounds in 0.1 M KOH solution as supporting electrolyte at scan rate of 100 mVs-1. The effect of scan rates and concentrations were studied and the effects show good linear relationship with the peak currents. The cyclic voltammetric behavior of Ni(II) ions were also examined in 1 M KCl solution as supporting electrolyte. The Ni(II) ions shows well defined redox peaks in presence of potassium ferricyanide as a mediator.

The electrochemical behaviour of six aryl hydrazones containing 1,3,4-oxadiazole moiety and pyrazoline-3-one moiety was described by DC polarography. The obtained results were compared with those obtained in cyclic voltammetry (CV) employing hanging mercury drop electrode (HMDE) and modified carbon paste electrode (MCPE). Based on the results, mechanism for the electro-reduction process was proposed in acid as well in basic media. The structure of aryl hydrazones were characterized by elemental analysis, IR and 1H NMR spectra.

Partial least squares (PLS) regression and principal component regression (PCR) multivariate calibration methods have been applied for the simultaneous determination of paracetamol (PAR) and p-aminophenol (PAP) using kinetic data obtained by novel potentiometric method. The method is based on the rate of chloride ion production in reaction of PAR and PAP with N-chlorosuccinimide (NCS) which is monitored by a chloride ion-selective electrode. The production rate of chloride ions in the reaction of PAR and PAP with NCS is different so that PLS and PCR can be applied to analyze the experimental potentiometric data. The determination of PAR and PAP is performed in the concentration ranges of 0.50-65.0 and 0.10-75.0 μg mL-1, respectively. The total relative standard errors in PLS and PCR methods were calculated to be 4.07 and 4.74 for PAR and 3.93 and 4.79 for PAP, respectively.

Spectrofluorimetric studies on the binding properties of Tris (3-(2-hydroxyacetophenone)propyl) amine) (L) toward different heavy metal ions in acetonitryl solution revealed its selective 1:1 complexation with Zinc ion. Consequently, L was used as a suitable ionophore for the preparation of new plasticized PVC membrane-selective electrodes for the determination of Zinc ion. The sensor exhibits a Nernstian response for Zn(II) over a wide concentration range (2.0×10-7-1.0×10-1 M) and detection limit of (9.6 ×10-8 M). The best performance was obtained with a membrane composition of PVC (30%), orthonitrophenyloctyl ether (o-NPOE) (64%), ionophore (L) (5%) and Potassium tetrakis(KTpCIPB) (1%). The sensor exhibits the advantages of fast response time (12 seconds),operational lifetime (24 weeks) and good selectivity co-efficient for Zn(II) over an alkali, alkaline earth and transition metal ions. The electrode was used as indicator electrode inpotentiometric titration of Zn(II) with ethylenediaminetetraacetic acid (EDTA) and in thedetermination of Zn2+ ion in real samples.