Perfluoro and sulfonated ion-exchange polymers are recognized as a very useful material for various mechanistic studies and applications in electrochemistry. These polymers are characterized by high equivalent weights and by a low number of ion-exchange sites interposed between long organic chains. The solubility enables a preparation of stable polyelectrolyte films on the electrode surface. Examples of the determination of trace metals and organic componds in real environmental samples are presented.

Chemically modified electrodes (CMEs) have been subject of considerable attention since its inception about 23 years ago. CMEs result of a deliberate immobilization of a modifier agent onto the electrode surface obtained through chemical reactions, chemisorption, composite formation or polymer coating. This immobilization seeks transfer the physicochemical properties of the modifier to the electrode surface and thus to dictate and control the behavior of the electrode/solution interface. In recent years the interest in CMEs has increased particularly to enhance the sensitivity and/or the selectivity of electroanalytical techniques. In general higher sensitivity and/or selectivity may be achieved by exploiting one or more of the following phenomena: electrocatalysis, preconcentration and interferents exclusion. This paper deals with the application of CMEs in electroanalysis, including a brief presentation of the more general procedures that have been employed for the modification of electrode surfaces.

Perfluoro and sulfonated ion-exchange polymers are recognized as a very useful material for various mechanistic studies and applications in electrochemistry. These polymers are characterized by high equivalent weights and by a low number of ion-exchange sites interposed between long organic chains. The solubility enables a preparation of stable polyelectrolyte films on the electrode surface. Examples of the determination of trace metals and organic componds in real environmental samples are presented.

The most relevant advances on the analytical applications of glutathione determination based on glutathione redox cycle and the antioxidant system are given. The main enzymes that participate of the glutathione metabolism are the glutathione peroxidase and glutathione reductase. The glutathione peroxidase has a major role in the removal of hydrogen peroxide and lipid peroxides from the cells. These enzymes, operating in tandem with catalase and superoxide dismutase promote a scavenging of oxyradical products in tissues minimizing damages caused by these species. Reduced glutathione is the major intracellular thiol found in mammals and changes in the glutathione concentration in biological fluids or tissues may provide a useful marker in certain disorders like hemolytic anemia, myocardial oxidative stress and in the investigation of some kinds of cancers. Particular attention is devoted to the main advantages supplied by biosensors in which there is an incorporation of bioactive materials for the glutathione determination. The correlation between stability and sensitivity of some reduced glutathione electrochemical sensors is discussed.

This paper reports the development of a glassy carbon electrode modified with a reduced graphene oxide (r-GO/GCE) for the determination of the food dye named Ponceau 4R (PNC). The modified sensor presented excellent signal gain in relation to the GCE and GCE modified with graphene oxide besides exhibiting well defined oxidation peaks for PNC at potential of 0.61 V. Through the application of square wave voltammetry using the medium of 0.1 mol L-1 Britton-Robinson (BR) buffer (pH 5.0), analytical curves were constructed under optimized conditions, where linear regions were found within the range of 0.200 to 20.0 μmol L-1. The limits of detection and quantification were 2.84 × 10-8 and 9.46 × 10-8mol L-1, respectively. The sensor was successfully applied towards the determination of PNC in instant juice sample. A comparison made between the result obtained through the application of this sensor and via the high-performance liquid chromatography (HPLC) technique showed no significant difference between the two methods.

This paper describes a comparative study between the procedures of deconvolution and the second-order derivative of square wave voltammograms to achieve separation of the voltammetric peaks of levofloxacin (LEVO) and norfloxacin (NOR), for their simultaneous quantification in urine samples. The obtained results indicate that the use of second-derivative voltammograms coupled with carbon screen-printed electrodes is the most efficient approach for completely separating the voltammetric peaks of LEVO and NOR. In addition, this approach has produced detection limits lower than 1.0 µmol L-1 and a wide linear range for both drugs. The proposed method was successfully used to simultaneously determine LEVO and NOR in spiked human and bovine urine samples with recovery percentages close to 100% for all analyzed samples.

In this study, a facile sensor based on TiO2 nanoparticles modified carbon paste electrode was developed for voltammetric determination of pramipexole in pharmaceutical formulations and biological samples. Surface of the fabricated electrode have been characterized using field emission scanning electron microscopy. Under the optimized experimental conditions, the modified electrode was exhibited excellent electrocatalytic activities and a sensitive oxidation peak at 0.9 V in the phosphate solution of pH 5.0 for electrooxidation of pramipexole. The plot of pH vs. Ep generated a slope of 62.5 mV per pH in the pH range of 3.0-13.0 indicating the contribution of an equal number of electrons and protons in the electrode process. A differential pulse voltammetry method was developed in the concentration range of 0.46-100 μmol L-1 with a limit of detection of 0.14 μmol L-1. The proposed method is simple, rapid, and inexpensive and also showed good selectivity and sensitivity toward pramipexole.

This work describes the electrochemical performance of a novel composite based on nickel tetrasulfonated phthalocyanine (NiTsPc), deoxyribonucleic acid from calf thymus (CT-DNA) and reduced graphene oxide (rGO) for the electroanalysis of reduced β-nicotinamide adenine dinucleotide (NADH), through electrocatalytic oxidation. The modified electrode was denoted as CT-DNA/NiTsPc/rGO. Fourier transform infrared and ultraviolet-visible spectroscopies were performed to characterize the composite material. The electrochemical performance of the composite for NADH oxidation was investigated by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). The CT-DNA/NiTsPc/rGO modified glassy carbon electrode (GCE) showed an excellent electrocatalytic activity for NADH oxidation with apparent electrocatalytic rate constant (kobs) of 7.35 × 105 L mol-1 s-1 and linear response range for NADH from 1 up to 1350 µmol L-1 for n = 12 (r = 0.999). The proposed sensor shows sensitivity, detection limit and quantification limit of 0.014 µA L mol-1, 0.3 and 1 µmol L-1, respectively. The prepared sensor was further tested for the determination of NADH in artificial human urine samples, showing promising biomedical applications.

This paper presents a proposal for using recycled graphite electrodes obtained from exhausted commercial 1.5 V batteries and its application in electroanalysis. The electrode could be prepared by the students and applied in the simple didactic experiments suggested, such as determination of active electrode area, cyclic voltammetry and useful potential range (also called "potential window"), demonstration and effect of scan rate on cyclic voltammograms. The possibility of using the graphite electrode in quantitative analysis was also demonstrated using the ferricyanide/ferrocyanide reversible redox couple ([Fe(CN)6]3-/[Fe(CN)6]4-) as an electrochemical probe by the dependence of peak current with the analyte concentration and flow injection analysis with amperometric detection.

Parabens are antimicrobial preservatives widely used in pharmaceutical, cosmetic and food industries. The alkyl chain connected to the ester group defines some important physicochemical characteristics of these compounds, including the partition coefficient and redox properties. The voltammetric and computational analyses were carried out in order to evaluate the redox behavior of these compounds and other phenolic analogues. A strong correlation between chemical substituents inductive effects of parabens with redox potentials was observed. Using cyclic voltammetry and glassy carbon working electrode, only one irreversible anodic peak was observed around 0.8 V for methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), benzylparaben (BzP) and p-substituted phenolic analogues. The electrodonating inductive effect of alkyl groups was demonstrated by the anodic oxidation potential shift to lower values as the carbon number increases and, therefore the parabens (and other phenolic analogues) oxidation processes to the quinonoidic forms showed great dependence on the substituent pattern.