Aplicação da Análise por Injeção em Batelada com Detecção Amperométrica para a determinação de ácido fólico em formulações farmacêuticas

Abstract

The present work presents the studies on the electrochemical oxidation of folic acid and its determination using a Batch Injection Analysis (BIA) system with the conventional amperometry technique. The tests were performed using the pyrolytic graphite sheet electrode (GSE) as a working electrode, which is a great sensor for electrochemical analysis. Cyclic voltammetric studies were performed to obtain information on the redox behavior of the analyte. Different buffer solutions were used to observe the behavior of the molecule in different media and pHs, for this, cyclic voltammograms were performed using acetate buffer, phosphate buffer and varying the pH of a Britton-Robinson buffer solution. It was observed that the behavior on the GSE provides a favored oxidation peak for folic acid in pH 7 (neutral medium), in this way, the supporting electrolyte chosen was a 0.1 mol L-1 Britton-Robinson (BR) buffer at pH 6. After the choice of supporting electrolyte, a hydrodynamic voltammogram was performed in order to evaluate the best working potential for the other analyses, and the optimum working potential was +1,0 V. The parameters of the BIA system were optimized, in 193 μL s-1 for flow rate and 200 μL for injection volume, respectively. During the studies it was observed the need to use a stirring system to reduce problems of folic acid adsorption on the surface of the GSE electrode, which was therefore adopted in this work. The developed method was applied to four different samples, tablets containing 2 or 5 mg of folic acid. Satisfactory responses were obtained, for example, a good analytical frequency (61 h-1), good detection limit (0.023 μmol L-1), relative standard deviation within the acceptable value (DPR <2.8%), attesting a good precision of the method, in addition to adequate sensitivity (2.08 x 10-1 μA L μmol-1). The HPLC method was used to compare the results obtained by the proposed method, and according to the paired Student's t test the results are concordant with 95% confidence.