Analytical & Bioanalytical Electrochemistry
Volume:1 Issue: 4, Dec 2009

Electrooxidation of 4-chlorocatechol at a glassy carbon electrode (GCE) was investigated in the presence of some biologically important thiols (RSH), e.g. Dpenicillamine (D-PA), glutathione (GSH) and L-cysteine (L-Cys) in aqueous media using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and double step potential chronoamperometry methods. The 4-chlorocatechol exhibits strong electrochemical response toward thiols oxidation in wide pH rang (2.00–9.00). The results show that thiol-containing compounds participate in Michael addition reactions with 4-chlorocatechol to form the corresponding thioquinone derivatives. The reoxidation of the adduct leads to an increase in the anodic current. Therefore, in the optimum condition (pH=6.00) in CV, the oxidation of D-PA, GSH and L-Cys in the presence of 4-chlorocatechol occur at a potential about 420, 750 and 420 mV, respectively less positive than that in the absence of it. The kinetic parameters such as electron transfer coefficient, α and electrochemical reaction rate constant, kh was determined using electrochemical approaches.

Electrochemical oxidation of 4-tert-butylcatechols (1) has been studied in the presence of N,N'-dimethylamino ethanthiol (3) as nucleophile in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate the quinone derived from the oxidation of 4-tert-butylcatechols (1) participates in a Michael addition reaction with N,N'-dimethylamino ethanthiol (3) to form the corresponding arylsulfonylbenzenediol 4 as the final product. Based on an EC mechanism, the observed homogeneous rate constants of reaction of some catechol derivatives and 3 were estimated by comparison the experimental cyclic voltammograms with the digital simulated results.

Voltammetric methods were used for the determination of hydrazine and investigation of its electrochemical behavior on a glassy carbon electrode in the presence of calmagite as a homogeneous mediator. The key factors considered in the optimization process were pH, mediator concentration and scan rate. The results showed with optimizing pH, mediator concentration and scan rate, the convenient selectivity of potential and current of hydrazine oxidation can be achieved. Calmagite as a mediator can catalyze the hydrazine oxidation in an aqueous buffer solution (pH=8.0). The apparent catalytic rate constant, k and diffusion coefficient, D of hydrazine were obtained as (1.2×104 M-1s-1) and (4.23×10-5cm2 s-1), respectively. The calibration curve was linear in the rang of 10.0 – 800.0 μM hydrazine, and the detection limit was 5.3 μM by linear sweep voltammetry, also differential pulse voltammetric determination of hydrazine exhibits two linear range of 1.0-20.0 and 40.0-800.0 μM and detection limit was 0.8 μM.

The corrosion and passivation of tin anode in citrate (0.01 to 1.0 M) solution was investigated using steady state polarization, impedance spectroscopy and cyclic voltammetric techniques. Before permanent passive region, two anodic peaks were observed in the anodic polarization curve, corresponding to the consecutive electroformation of Sn(II) and Sn(IV) species. The corrosion current was calculated by the Tafel extrapolation procedure at different concentrations of citrate ion and different pH values. Also, the corrosion resistance at the corrosion potential was calculated from the Nyquist diagram of different concentration of citrate ion. It was found the latter gives more precise results.

A molecularly imprinted polymer material having urea molecule selective cavities was prepared. It was shown that the MIP had a considerable selectivity for urea in comparison to similar compounds such as thiourea. The obtained polymer was used as an adsorber for solid phase extraction (SPE) of urea from aqueous samples. The polymer containing urea was then washed with water/ethanol mixture and subsequently it was contacted with free chorine solution. Cl- ions, produced by reaction of hypochlorite and urea, was determined via a Cl- selective electrode. Some different parameters of SPE were optimized and the developed procedure was used for urea determination in real sample.