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A simple and sensitive electrochemical method was developed for the determination of N-Acetylcysteine (NAC) and Glutathione (GSH), on glassy carbon electrode. The results indicate that α-lipoic acid (LipS2) is oxidized at the electrode, but is regenerated by thiols, suggesting a redox catalytic effect. Under optimized conditions, the analytical curves for NAC and GSH were obtained in the range of 1 up to 10 µM and 1 up to 60 µM, respectively. The quantification can be performed in a single assay with high sensitivity, reproducibility and low detection limit of 0.27 and 0.67 µM for NAC and GSH, respectively. This method was successfully applied to the determination of NAC and GSH in artificial saliva and human urine samples, with excellent recovery results.

This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0–150.0 µmol/L (r = 0.997), a limit of detection (3σ) of 2.0 µmol/L, a sample throughput of 164 determinations per hour, reagent consumption of 9 µg luminol and 42 µg hypochlorite per determination and generation of 0.63 mL of waste. A relative standard deviation of 1% (n = 6) for a standard solution containing 80 µmol/L captopril was also obtained. Copyright © 2015 John Wiley & Sons, Ltd.

The present work describes the development of a selective and sensitive voltammetric sensor for simulta- neous determination of catechol (CC) and hydroquinone (HQ), based on a glassy carbon (GC) electrode modified with manganese phthalocyanine azo-macrocycle (MnPc) adsorbed on multiwalled carbon nanotubes (MWCNT). Scanning electron microscopy and scanning electrochemi- cal microscopy were used to characterize the composite material (MnPc/MWCNT) on the glassy carbon electrode surface. The modified electrode showed excellent electro- chemical activity towards the simultaneous oxidation and reduction of CC and HQ. On the MnPc/MWCNT/GC electrode, both CC and HQ can generate a pair of quasi- reversible and well-defined redox peaks. Under optimized experimental and operational conditions, the cathodic peak currents were linear over the range 1-600 mmol L � 1 for both CC and HQ, with limits of detection of 0.095 and 0.041 mmol L � 1 , respectively. The anodic peak cur- rents were also linear over the range 1-600 mmol L � 1 for both CC and HQ, with limits of detection of 0.096 and 0.048 mmol L � 1 , respectively. The proposed method was effectively applied for the simultaneous detection of hy- droquinone and catechol in water samples and the results were in agreement with those obtained by a comparative method described in the literature.

Real-time monitoring of the electrochemical degradation of acetaminophen was performed using a biomimetic sensor coupled to a flow injection analysis (FIA) system. Degradation of the drug was carried out at constant current density (24 to 180 mA cm−2) in an electrolyte consisting of 0.1 mol L−1 K2SO4/5.0×10−4 mol L−1 FeSO4⋅7H2O. Two commercial DSA anodes (DSA-Cl2 and DSA-O2) were compared. The degradation process was monitored on-line using an amperometric sensor based on the biomimetic catalyst iron(III) tetrapyridinoporphyrazine (FeTPyPz), coupled to the degradation cell. The optimized FIA detection system employed the electrolyte solution as carrier, a flow rate of 1.25 mL min−1 and an injected sample volume of 75 µL. The real-time data obtained showed, as expected, that acetaminophen degradation followed pseudo-first order kinetics, with the DSA-Cl2 anode showing a higher efficiency according to the calculated apparent rate constant values. The advantage of the proposed on-line system is that a larger number of points can be monitored in a shorter time compared to other off-line methods, which improves the accuracy of estimates of electrochemical degradation constants.

Organically modified silicates (ORMOSILs) are attractive materials due to their vast applicability and easy synthesis. The doping of these materials with sodium dodecyl sulfate (SDS) is interesting in the search for good protonic conductors. The inclusion of different concentrations of SDS in ORMOSIL membranes is investigated in the present work using Raman and infrared spectroscopy, confocal Raman microscopy and confocal imaging microscopy. The spectroscopic measurements allow us to assign the vibrational modes to the chemical groups of the structures of SDS and ORMOSIL. Furthermore, these measurements show that these materials are composites, as no interactions are observed between the SDS and the ORMOSIL matrix. The confocal Raman and confocal imaging techniques are useful to study qualitatively the SDS insertion on the surface of ORMOSIL. It was observed that the SDS sizes are very nonuniform. Copyright © 2011 John Wiley & Sons, Ltd.

The present work describes the development of a highly sensitive amperometric sensor for 4-NP in nanomolar levels using a glassy carbon electrode modified with alternating layers of CuTSPc and FeT4MPyP. After optimizing the operational conditions, the sensor provided a linear response range for 4-NP from 5 up to 100 nmol L−1 with sensitivity, detection, and quantification limits of 14 nA L nmol−1, 1.9 nmol L−1, and 5.4 nmol L−1, respectively. The proposed sensor showed a stable response for at least 200 successive determinations. This modified electrode can be used to the determination of 4-NP in water samples.

The use of [Cu(bipy)2]Cl2⋅6H2O as a biomimetic catalyst in the construction of an amperometric sensor for dopamine determination is reported. The sensor was prepared modifying a glassy carbon electrode with a Nafion membrane doped with [Cu(bipy)2]Cl2⋅6H2O complex. The sensor presented a higher response in 0.25 mol L−1 phosphate buffer solution (pH 7.0), with an applied potential of −50 mV (vs. SCE). In the optimized operational conditions, a linear response range between 35 and 240 μmol L−1, with a sensitivity of 2.02±0.07 nA l μmoL−1 cm−2 and detection limit of 8.0 μmol L−1 were typically observed for the sensor. The response time presented for this sensor was 0.5 s, presenting the same response for at least 40 successive measurements, with good repeatability (3.0%) expressed as relative standard deviation for n=6. The difference of the response between four sensor preparations was 4%. A detailed investigation about the sensor response for other sixteen phenolic compounds and interfering species were carried out. The sensor was applied in the determination of dopamine in pharmaceutical preparation with success.

Nickel tetrasulfonated phthalocyanine (NiTsPc) immobilized onto titanized silica gel (ST) showed good stability and redox properties. The cyclic voltammograms obtained with a carbon paste electrode modified with ST-NiTsPc presented an enhanced peak current at 450 mV (vs. SCE) which did not shift with solution pH. The redox process was attributed to NiII/NiIII, which presented a good electrocatalytical activity for oxidizing hydrazine in neutral solution. The process is controlled by the electron transfer step and no diffusion limitation was observed. The modified electrode was very sensitive for hydrazine, giving a detection limit of 1.0 × 10−5 mol L−1, for an applied potential of 450 mV (vs. SCE). A linear response range was observed between 1.0 × 10−4 and 6.0 × 10−4 mol L−1, fit by the equation I = −0.1 (± 0.1) + 7.9 (± 0.3) [Hydrazine], with a correlation coefficient of 0.998 for n = 6. The repeatability for 11 measurements was excellent, with a relative standard deviation of 3.7 %. The active material, nickel tetrasulfonated phthalocyanine modified silica, was stable for at least 6 months, losing only 10 % of its signal over this period.

The underpotential deposition (UPD) of Cu on Pt was studied in acid media using cyclic voltammetry and rotating ring-disk electrode techniques. Experimental data at sub-monolayer levels demonstrate that ad-atom formation occurs in different energy states and no rearrangements take place in the ad-layer. Rotating ring-disk studies of the oxygen reduction reaction on Cu UPD show a strong inhibition of the reaction only in the region of diffusion control. At first, the 4 e reaction to H 2 O is inhibited in favor of the 2 e reaction to H 2 O 2 but at more negative potentials even the formation of H 2 O 2 is inhibited. A mechanism based on the degree of surface-active sites blocked by Cu ad-atoms is proposed.

Transition metal complexes of planar metallomacrocycles, including ligand systems such as the porphyrins and phthalocyanines, have been studied in depth as precursors for 1-dimensional conductors. These complexes have several key features in common: the molecules are planar with an extend pi-system, the ligand atoms which complex the metal are relatively hard nitrogen donors, the ligand has a formal negative oxidation state and the complexes can be made conductors by either oxidation or reduction. The present work shows that the reaction of Ni(COD)2 with TBC in benzene affords a Ni(O) complex in which the nickel atom resides in the cavity of the twelve membered ring equally bound to all three alkynes. The synthesis, characterization and reaction chemistry of Ni(TBC) is presented below. In addition, the preparation of n-doped macrocyclic conductors based upon TBC and NI(TBC) are reported. Keywords: Nickel compounds, Nickel.