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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.

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.

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.