Chloroquine is a drug belonging to the aminoquinoline family that is widely used for treating diseases such as lupus, cancer, and malaria. In this sense, the present work describes the development of a simple method based on electrogenerated chemiluminescence (ECL) and a screen-printed carbon electrode (SPE) modified with carbon black for chloroquine determination. The carbon black modified SPE was characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry and linear sweep voltammetry to obtain the ECL-potential curves. The ECL method is based on the chemiluminescence resulting from the interaction between chloroquine and the tris(2’2-bipyridyl) ruthenium(II) complex. Under optimized experimental conditions, the method showed a wide linear working range between 0.5 and 500 µmol L-1. The method presented good precision and accuracy in drug samples used in the treatment of malaria and artificial urine sample, showing recovery values from 100 to 103% and 99 to 103%, respectively.

The present work is based on the development and application of a photoelectrochemical method for the amperometric determination of 3,4,5-trihydroxybenzoic acid in different samples. The method is based on the use of a photoelectrochemical platform based on a glass slide coated with fluorine-doped tin oxide, which has been modified with cadmium sulfide and poly(D-glucosamine) and subjected to a light-emitting diode (LED) lamp. The photoelectrochemical platform was sensitive to the increase of the concentration of the antioxidant 3,4,5-trihydroxybenzoic acid in the solution. Under the optimized experimental conditions, the photoelectrochemical method presented a linear response for a 3,4,5-trihydroxybenzoic acid concentration ranging from 0.2 up to 500 µmol L-1. The method was applied to 3,4,5-trihydroxybenzoic acid determination in samples of wines and teas with recoveries between 95.88 and 101.72%. The results obtained suggest that the developed platform is a promising tool for quantifying the 3,4,5-trihydroxybenzoic acid.

The present work presents the development of a sensitive and selective amperometric sensor for the determination of hydrazine (HZ) in pharmaceutical formulations using a glassy carbon electrode (GCE) modified with a composite based on Co(Salophen), reduced graphene oxide (rGO) and deoxyribonucleic acid (DNA). The rGO/Co(Salophen)/DNA composite was characterized by using Fourier-transform infrared spectroscopy (FTIR), cyclic voltammetry, and amperometry. The proposed platform presented a well-defined voltammetric profile with a redox couple around 0.32 V vs. Ag/AgCl which showed excellent catalytic activity towards HZ oxidation. The peak current of HZ electrochemical oxidation on the proposed electrochemical platform have changed linearly with the HZ concentration in the range from 2 to 364 µmol L-1. The proposed platform presented sensitivity, limit of detection, and limit of quantification of 0.056 µA L µmol-1, 0.54 µmol L-1, and 1.64 µmol L-1 to HZ, respectively. The relative standard deviation for eight determinations using a solution of 50 µmol L-1 HZ was 0.85%. The proposed sensor was successfully applied for the determination of HZ in pharmaceutical formulations, and the recovery tests showed a good accuracy with recovery percentage between 99 and 101%.

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.

A construção de um sensor amperométrico para compostos fenólicos usando um eletrodo de pasta de carbono modificado com ftalocianina de manganês e histidina é relatado. Sob condições otimizadas, em 0 mV vs Ag/AgCl numa solução tampão fosfato 0,1 mol dm-3 (pH 7,0) contendo H2O2 250 µmol dm-3, uma resposta linear para catecol entre 20 e 130 µmol dm-3, com sensibilidade de 0,56 (± 0,02) µA dm³ mol-1 cm-2, foi obtida. O limite de detecção foi 1,1 µmol dm-3 e o tempo de resposta foi de 2 s. O sensor apresentou resposta estável durante 40 determinações sucessivas. A repetibilidade avaliada em termos de desvio padrão relativo foi de 3,6% para n = 5 e [catecol] = 10 µmol dm-3. As respostas do sensor para outros compostos fenólicos também foram investigadas em detalhes. Finalmente, a aplicabilidade do sensor foi testada em medicamento contendo dopamina e os resultados comparados favoravelmente com os obtidos com o método oficial.

The construction of an amperometric sensor for phenolic compounds using a carbon paste electrode modified with manganese phthalocyanine and histidine is reported. Under optimized conditions, at 0 mV vs Ag/AgCl in 0.1 mol dm-3 phosphate buffer solutions (pH 7.0) containing 250 µmol dm-3 H2O2, a linear response for catechol from 20 up to 130 µmol dm-3 was obtained with a sensitivity of 0.56 (± 0.02) µA dm³ µmol-1 cm-2. The detection limit was 1.1 µmol dm-3 and the response time was 2 s. The sensor presented stable response during 40 successive determinations. The repeatability, evaluated in terms of relative standard deviation, was 3.6% for n = 5 and [catechol] = 10 µmol dm-3. The sensor responses for other phenolic compounds were also investigated in details. Finally, the applicability of the sensor was tested in a pharmaceutical containing dopamine and the results compared favorably with those obtained with the official method.