Desenvolvimento de metodologias baseadas em sistemas miniaturizados com aplicações em química analítica

Abstract

Miniaturized systems have unique characteristics that enable their applications in several fields of knowledge. The low cost per analysis, portability and the possibilities of hyphenating the most diverse analytical techniques are attributes that have been attracting the attention of the scientific community since the 1990s. In this work, two different methodologies using miniaturized systems are presented. The first methodology uses paper-based analytical devices (PADs) for colorimetric determination of ranitidine through the reaction of the analyte with the probe 4-Chloro-7-nitrobenzofurazan (NBD-Cl). Ranitidine is a histamine H2 receptor antagonist used in the treatment of gastroduodenal ulcers and related diseases, such as gastroesophageal reflux and Zollinger-Ellison syndrome. Many analytical methods have been reported for the determination of ranitidine, including electrochemical, spectrophotometric, fluorescence, and chemiluminescence. Although these methods are suitable for the determination of ranitidine in different samples, they have major disadvantages, including high cost and reagent consumption, laborious operation, complex equipment, and trained personnel. Analytical parameters such as pH, type of buffer, concentration of reagents and temperature were optimized for the proposed methodology. Under optimal conditions, the analysis system used phosphate buffer (pH 8.0; 30mM), with the addition of NBD-Cl (0.8µL, 20mM). the method presented a linear range of 0.2 – 1.5 mmol L-1, corresponding to the equation [(MbMr)/Mb]=43,04(±1,28)Cranitidine-9,48x10-13%±5,52x10-8 & and linear correlation coefficient r = 0.9982. Recovery tests with real samples showed values between 90.90% and 109.27%. Furthermore, this methodology proved to be suitable for application in pharmaceutical samples and is a simple, cheap and quick alternative for the determination of ranitidine. The second methodology developed in this work used an electrophoresis microchip system with electrochemical detection (ME-EC) for the separation and determination of biological thiols (glutathione and cysteine) and ascorbic acid. These species play a fundamental role in human physiology and protect cells from reactive oxygen and nitrogen species, being fundamental for cellular homeostasis. The concentrations of these species in humans indicate levels of oxidative stress and may suggest the need for treatment for diseases such as diabetes and cancer. Using a PDMS/glass hybrid microchip, the methodology was based on the reaction of thiols with menadione, the product being of this reaction analyzed via ME-EC. Parameters such as buffer composition, use of surfactants and cyclodextrins were optimized. Thus, the system was optimized with a detection potential of +0.4 V, HEPES buffer (pH 8.5; 30mM) with the addition of 8mM SDS SBE-ß-CD at 2mM. The methodology made it possible to construct analytical curves for each of the analytes with linear correlation coefficients above 0.995. Furthermore, the linear ranges were 2.5 – 100 µM for glutathione and 5 – 50 µM for both cysteine and ascorbic acid. The main advantages of the proposed methodology are the low detection potential, ease in carrying out the experimental steps and feasibility for analyzing complex samples such as human plasma and erythrocytes.