Novas abordagens para determinação de melatonina e metabólitos em leite materno e aplicação da metabolômica para fins de diferenciação de cultivares de alface

Abstract

In analytical chemistry, there is a constant search for methodologies that require less cost and analysis time, but at the same time offer precision and accuracy. In this sense, various methodologies and technologies have been evaluated, among which we can highlight those that employ miniaturized sample preparation techniques and those that use ambient ionization sources for mass spectrometry. This thesis is divided into two chapters presenting the potential of modern sample preparation techniques for liquid chromatography analysis and ambient mass spectrometry analysis. The first chapter describes the use of disposable pipette extraction, utilizing a sorbent phase based on molecularly imprinted polymers (DPX-MIP), for the determination of melatonin and its metabolites (AFMK and AMK) in breast milk by liquid chromatography coupled with mass spectrometry (LC-MS). Different MIPs were synthesized and evaluated for their selectivity in analyzing melatonin and its metabolites, experimentally obtained results were compared with molecular simulation data, showing consistency between the theoretical physicochemical parameters and the experimental data. The application of DPX-MIP in conjunction with LC-MS enabled the development of a method for determining melatonin and its metabolites in breast milk, with recovery values ranging from 87-111% and precision between 2-13%, analysis of patient samples produced values consistent with those reported in the literature. The second chapter explores the application of the paper spray ionization mass spectrometry (PSI-MS) technique to study the metabolomics of lettuce cultivars and the potential differentiation according to their cultivation method and variety. PSI-MS, an ambient ionization technique, uses chromatographic paper as a substrate for the sample ionization process. In this study, lettuce samples were successfully differentiated according to variety and cultivation method through the application of chemometric tools (PARAFAC, PCA, PLS-DA, and OPSDA), identifying 36 metabolites responsible for this differentiation, with choline, mannose, and citric acid being the most influential. Additionally, green chemistry metrics, such as AGREEprep and AGREE, were applied to assess the sustainability of the developed methodologies. The results confirmed that DPX-MIP and PSI-MS are more sustainable, offering appropriate analytical performance with shorter analysis times and generating low volumes of chemical waste