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In the present paper, we use a gold electrode modified by a 2-(3, 4- dihydroxy phenyl) benzothiazole self-assembled monolayer (DHT-SAM) for determination of epinephrine (EP) and Uric Acid (UA). Initially, DHT-SAM was characterized by different techniques. CV was used to investigate the redox properties of the modified electrode at various scan rates. The apparent charge transfer rate constant, ks and transfer coefficient (α) were calculated. Next, electro oxidation of epinephrine (EP) and Uric Acid (UA) on a gold electrode modified by a self-assembled monolayer of DHT mediated was investigated. At the optimum pH of 7.0, the oxidation of EP occurs at a potential about 200 mV less positive than that of an unmodified gold electrode. The values of transfer coefficients (α = 0:35), catalytic rate constant (k = 4:4 × 104M-1s-1) and diffusion coefficient (D = 1:03×10-6 cm2s-1) were calculated for EP, using electrochemical approaches. Differential Pulse Voltammetry (DPV) exhibited a linear dynamic range over a concentration range of 0.5-400.0 μM and a detection limit (3s) of 0.11 μM for EP in pH = 7. Finally, simultaneous determination of EP and UA at the modified electrode was described and used for determination of EP in the EP ampoule. [ABSTRACT FROM AUTHOR]

A carbon paste electrode (CPE), modified with novel hydroquinone/TiO2 nanoparticles, was designed and used for simultaneous determination of ascorbic acid (AA), uric acid (UA) and folic acid (FA). The magnitude of the peak current for modified TiO2-nanoparticle CPE (MTNCPE) increased sharply in the presence of ascorbic acid and was proportional to its concentration. A dynamic range of 1.0-1400.0 μM, with the detection limit of 6.4 × 10-7 M for AA, was obtained using the DPV technique (pH = 7.0). The prepared electrode was successfully applied for the determination of AA, UA, and FA in real samples. [ABSTRACT FROM AUTHOR]

Abstract: A modified carbon paste electrode was prepared by incorporating TiO2 nanoparticles with bis[bis(salicylidene-1,4-phenylenediamine)molybdenum(VI)]. A mixture of fine graphite powder with 4wt% of TiO2 nanoparticles was applied for the preparation of the carbon paste (by dispersing in paraffin) and finally modified with a molybdenum (VI) complex. The electrocatalytic oxidation of guanine (G) was investigated on the surface of the molybdenum (VI) complex–TiO2 nanoparticle modified carbon paste electrode (MCTNMCPE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry (CHA) and chronocoloumetry (CHC). Using the modified electrode, the kinetics of G electrooxidation were considerably enhanced by lowering the anodic overpotential through a catalytic fashion. The mechanism of G electrochemical behavior at the modified electrode surface was analyzed by various electrochemical methods. The prepared modified electrode showed voltammetric responses with high sensitivity for G, making it very suitable for the detection of G at nanomolar levels. A linear dynamic range of 7.0–200nM for G was obtained in buffered solutions with pH 5.0. The detection limit was 3.4nM. [Copyright &y& Elsevier]

Polypyrrole modified electrode, prepared by electropolymerization of pyrrole in the presence of methyl red as a dopant, was templated with respect to Pb2+ ion and applied for potentiometric and voltammetric detection of this ion. The templating process improved the analytical response characteristics of the electrode, specially their selectivity, with respect to Pb2+ ion. The improvement depends on both the incorporated ligand (dopant) and the templating process, with the latter being more vital. The potentiometric response of the electrode was linear within the Pb2+ concentration range of 2.0×10-6 to 5.0×10-2 M with a near-Nernstian slope of 28.6 mV decade-1 and a detection limit of 7.0 ×10-7 M. The electrode was also used for preconcentration differential pulse anodic stripping voltammetry (DPASV) and results showed that peak currents for the incorporated lead species were dependent on the metal ion concentration in the range of 1.0×10-8 to 1.0×10-3 M. The detection limit of DPASV method was 3.5 ×10-9 M. The selectivity of the electrode with respect to some transition metal ions was investigated. The modified-templated electrode was used for the successful assay of lead in two standard reference material samples.

The acid-base properties of calcon (1-(2-hydroxy-1-naphthylazo)-2- -naphthol-4-sulfonic acid) in water and mixed water-organic solvents at 25 °C at an ionic strength of 0.10 M are studied by a multiwavelength spectrophotometric method. The organic solvents used were the amphiprotic (methanol), dipolar aprotic (dimethylsulfoxide), and low basic aprotic (acetonitrile). To evaluate the pH absorbance data, a resolution method based on the combination of soft- and hard-modeling was applied. The acidity constants of all related equilibria were estimated using the whole spectral fitting of the collected data to an established factor analysis model. The data analysis program Datan was applied for determination of the acidity constants. The corresponding pKa values were determined in water and mixed water-organic solvents. Linear relationship between the acidity constants and the mole fraction of the different solvents in the mixtures exist. The effect of solvent properties on acid-base behavior is discussed.