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%.