Desenvolvimento e avaliação de estratégias espectrofotométricas para determinação de analitos em águas utilizando calibração multienergética (MEC)

Abstract

The determination of organic compounds in aqueous matrices is a growing need in environmental analytical chemistry, especially in regions of high ecological sensitivity, such as the Amazon. In this context, this project aimed to develop and evaluate spectrophotometric strategies in the ultraviolet-visible region for the determination of two analytes of different natures: methylene blue, used as a model system for direct spectral response, and glyphosate, a widely used herbicide that is difficult to detect by conventional spectrophotometry. For glyphosate, the approach of generating an analytical signal through complexation with Cu2+ ions was investigated. Concurrently, three calibration strategies were compared: external calibration (EC), standard addition (SA), and multi-energetic calibration (MEC). The study was applied to samples of tap water, well water, and methanol. The results obtained for methylene blue showed that all three methods exhibited excellent linearity (R² > 0.995), with MEC yielding a limits of detection and quantification of 0.001 and 0.003 mg L⁻¹, respectively, in addition to quantitative performance similar to that of traditional methods. For glyphosate, complexation with Cu²⁺ made it possible to obtain a spectrophotometric signal suitable for the application of MEC, with a detection limits of detection and quantification of 0.2 and 0.6 mg L⁻¹, respectively. The results also demonstrated that the choice of spectral region and the composition of the matrix directly influence the performance of MEC. Thus, MEC proved to be a viable alternative for applications in molecular spectroscopy, exhibiting performance comparable to traditional methods for methylene blue and showing potential for the spectrophotometric determination of glyphosate after complexation with Cu²⁺ ions.