Aplicação de sistemas de análise por injeção em batelada com detecção eletroquímica para determinação de substâncias bioativas

Abstract

The great demand of humanity for means that favor a long and healthy life has spurred research for new substances capable of meeting such needs. Among these substances are bioactive compounds that have several biological functions, such as antioxidant action, anti-inflammatory, protective against pathogenic microorganisms, inhibitor of the carcinogenesis process, protection against the incidence of ultraviolet rays, among others. Such compounds, once present in nature or in various products used in daily life, demand challenges directed to the development of analytical methodologies to determine their concentrations. Most techniques reported in the literature depend on early sample preparation steps that are time consuming; use a large amount of reagents (solvents) and expensive associated equipment, which increases the final cost of analysis. Therefore, it is necessary to develop fast, cheap and more sensitive techniques. In this sense, electrochemical techniques appear as viable and promising alternatives. Thus, this work presents simple, fast and low cost methods for the determination of catechin and quercetin bioactive substances using the conventional amperometric detection batch injection technique (BIA-AC) using printed carbon electrodes (ECI), and employing a glassy carbon electrode (ECV) with a multi-pulse amperometric detection BIA (BIA-MPA) system. The proposed BIA-MPA method is based on the application of three potential pulses (oxidation, cleaning and conditioning potentials) vs Ag / AgCl / KClsat, avoiding passivation by oxidation products and allowing quantification. The proposed methods presented satisfactory results. The BIA-MPA presented a linear range of 20 to 100 μmol L−1 (R = 0.999), with a detection limit (LD) of 0.03 μmol L−1 and a limit of quantification (LQ) of 0.10 μmol L−1 which made it possible to determine catechin in green tea samples and herbal extracts. The repeatability of the method for successive catechin injections at 50 μmol L−1 (n = 30) showed a relative standard deviation (RPD) of 0.85%. The BIA-AC method for catechin determination showed a linear range from 1 to 150 μmol L−1 (R = 0.999), with LD and LQ of 0.021 and 0.070 μmol L−1 and the stability of the method was evaluated with successive injections of 50 μmol L−1 catechin, presenting a DPR = 1.03% (n = 30). Both methods presented a sample rate of 120 injections per hour. In addition, quercetin determination using the BIA-MPA method was accurate (DPR 0.74%; n = 30), rapid (72 injections h−1) with low LD (0.004 μmol L−1) and LQ ( 10 μmol L−1). The application of BIA-

AC method was also accurate (1.06% DPR; n = 30) and fast (120 injections h−1), with LD of 0.027 μmol L−1 and LQ of 10 μmol L−1. Both methods presented linear range from 10 to 150 μmol L−1. Applications of these methodologies in the determination of quercetin in medicinal plant leaf extract samples showed results consistent with those obtained by high performance liquid chromatography (HPLC), with a 95% confidence level. The proposed methods demonstrated favorable results such as: low operating cost, simple sample preparation procedure (dissolution and dilution only), good analytical frequency, high precision, low reagent and sample consumption and, consequently, the generation of small amounts of residues by analysis. Additionally, the portability characteristics of BIA systems allow them to be applied in field analysis.