PPGQ https://repositorio.ufpb.br/jspui/handle/tede/7029 2026-08-08T16:48:16Z 2026-08-08T16:48:16Z Barreto, Matheus de Caldas https://repositorio.ufpb.br/jspui/handle/123456789/38477 2026-07-24T06:10:34Z 2025-10-30T00:00:00Z

Título: Metodologias eletroquímicas e espectroeletroquímicas de ordem superior para análise de matrizes complexas Autor(es): Barreto, Matheus de Caldas Orientador: Fragoso, Wallace Duarte Abstract: The effect of interferences is an important problem in Analytical Chemistry. Some approaches to deal with this problem are usually separation methods, deve-lopment of selective sensors, among others. There are also ways to mathematically separate the analyte signal, with it being acquired in multiple instrumental ways, extracting relevant information and gaining robustness to the interferences through mathematical properties. These are called multiway or higher-order methods. In this work, three methods based in electrochemical and spectroelectrochemical te-chniques were used to obtain multiway signals, applying them in the study of different systems. The first is a spectroelectrochemical method, combining chro-noamperometry and fluorescence. A proprietary cell and an interfacing system were developed for the experiment, with dopamine/epinephrine mixtures being used to test the methodology. Data was acquired in three ways (emission-time-potential) and the third-order models provided predictions with relative errors of prediction (REPs) of 1 to 2%, compared to the second-order models, presenting REPs of 9 to 40%, highlighting the advantages of expanding data dimensionality beyond second-order. The second method was the expansion of electrochemical impedance spectroscopy to a second order technique by varying the direct current potential. This method was applied to the quantification of paracetamol in urine, in the presence of added uric and ascorbic acid as interferents. Using the combi-nation of the real part of the impedance with the phase shift of the signal, it was possible to determine paracetamol in the range of 0.5 to 3.0 pmol.L¹ with a root mean squared error of prediction (RMSEP) of 0.38 pmol.L. Finally, the third method consisted of the application of multiway voltammetric techniques, creating models for the identification of synthetic cannabinoids in street samples (n = 48) The best performance was attained by models created with differential pulse vol-tammetry with gradual changes in pulse times, allowing the identification of drugs based on 8-quinoline indole-3-oate, indazole-3-amide and negative samples, with a 98.3% accuracy. Editor: Universidade Federal da Paraíba Tipo: Tese

2025-10-30T00:00:00Z Nóbrega, Rossana Oliveira da https://repositorio.ufpb.br/jspui/handle/123456789/38433 2026-07-23T06:13:05Z 2025-12-10T00:00:00Z

Título: Desenvolvimento de métodos voltamétricos para a determinação simultânea de aminas biogênicas em vinhos e cafés solúveis Autor(es): Nóbrega, Rossana Oliveira da Orientador: Araújo, Mário César Ugulino de Abstract: Monitoring biogenic amines in food and beverage products is essential to ensure compliance with quality standards and consumer food safety. In this work, two analytical methods based on square-wave voltammetry (SWV) were developed, employing different electrodes and strategies to obtain first- and second-order multivariate data. In the first study, a zinc phthalocyanine–modified carbon paste electrode (CPE–ZnPc) was employed to generate first-order data. The successful modification of the optimized electrode was confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Under optimized conditions (borate buffer, pH 9.2; f = 50 Hz, a = 30 mV, and ΔEs = 6 mV), the proposed method enabled the simultaneous determination of tyramine and spermidine in wine and instant coffee samples, achieving low limits of detection of 48.6 nmol L⁻¹ for tyramine and 76.9 nmol L⁻¹ for spermidine. The method exhibited satisfactory accuracy, with recoveries ranging from 86.1% to 107.5%, and good reproducibility (RSD of 2.6%). Moreover, high selectivity was observed, as no significant interference affected the electrochemical quantification of the target analytes in either matrix. Consequently, no sample pretreatment was required, which contributes to the principles of green analytical chemistry. In the second study, a boron-doped diamond (BDD) electrode was used to acquire second-order voltammetric data through pulse amplitude variation. Under optimized SWV conditions (Britton–Robinson buffer, pH 9.0; f = 70 Hz, a = 20–70 mV, and ΔEs = 8 mV), a method was developed for the simultaneous quantification of putrescine, cadaverine, and histamine, allowing the resolution of highly overlapping voltammetric signals. For this purpose, calibration models based on Partial Least Squares Unfolded with Residual Bilinearization (U-PLS/RBL) and Resolution of Multivariate Curves with Alternating Least Squares (MCR-ALS) were constructed using individual standard solutions in the linear concentration range of 0.92 to 7.46 μmol L⁻¹, with limits of detection between 50 and 100 nmol L⁻¹. Overall, the combination of conventional electrodes with multiway calibration methods proved to be a promising strategy for the analysis of biogenic amine mixtures. Although application to real samples remains a subject for future investigation, the results demonstrate strong potential for the development of methodologies aimed at the simultaneous determination of biogenic amines in food matrices without prior sample preparation. Editor: Universidade Federal da Paraíba Tipo: Tese

2025-12-10T00:00:00Z Arruda, Joaldo Garcia https://repositorio.ufpb.br/jspui/handle/123456789/38350 2026-07-17T06:11:26Z 2024-04-29T00:00:00Z

Título: Propriedades estruturais e luminescentes de novos compostos carboxilatos e β-dicetonatos de íons lantanídeos Autor(es): Arruda, Joaldo Garcia Orientador: Teotonio, Ercules Epaminondas de Sousa Abstract: In this research, two independent studies were conducted to investigate new lanthanide ion based compounds using carboxylate and β-diketonate ligands as luminescence sensitizers. In the first class, two different types of systems were explored: N-phthaloylglycine (phtgly) with N-(2-carboxybenzoyl) glycine (cbgly) or terephthalic acid (1,4-bdc), resulting in the formation of coordination polymers (CPs) with general formulas: {{[Ln2(phthgly)6(H2O)2]⋅(H2O)2}, {[Ln(phthgly)(cbgly)(H2O)2].(H2O)}, and {[Ln2(phthgly)4(bdc)(H2O)6](H2O)4}∞, as well as doped systems {[EuxTb1-x(phthgly)(cbgly)(H2O)2].(H2O)} (x= 0.25, 0.50, 0.75). On the other hand, the class of β-diketonate was used with auxiliary ligands, resulting in the formation of coordination compounds with general formulas [Ln(dbm)2(NO3)(L)2] and [Ln(dpm)(NO3)2(tchpo)2], where Ln: Eu3+, Tb3+, and Gd3+ and β-diketonate is represented by dbm: 2-diphenylmethane, dpm: dipivaloylmethane. The auxiliary ligands L include: tchpo (tricyclohexylphosphine oxide), topo (trioctylphosphine oxide), and tpAsO (triphenylarsine oxide). The synthesized systems were characterized using elemental microanalysis of C, H, and N, infrared absorption spectroscopy (FT-IR), diffuse reflectance, thermogravimetric analysis and nuclear magnetic resonance spectroscopy (NMR). Furthermore, the complexes {[Ln2(phthgly)6(H2O)2]⋅(H2O)2}, {[Ln2(phthgly)4(bdc)(H2O)6](H2O)4}∞, [Ln(dbm)2(NO3)(L)2] and [Ln(dpm)(NO3)2(tchpo)2] were obtained as single crystals, allowing their structures resolution by the single-crystal X-ray diffraction method. The luminescent properties were experimentally investigated based on spectral data of excitation, emission, and lifetime decay curves of the 5D0 emitting state and intrinsic quantum yield (𝑄𝐿𝑛𝐿𝑛). The spectra of the system {[Eu2(phthgly)4(bdc)(H2O)6](H2O)4}∞ showed that the intramolecular energy transfer processes are minimally operative, circumvented by the doping process with Tb3+ ions. Meanwhile, in the [Eu(dpm)(NO3)2(tchpo)2] system, very low luminescence intensity was observed due to an efficient luminescent quenching process via ligand-to-metal charge transfer (LMCT). Additionally, theoretical studies based on the Time-Dependent Density Functional Theory (TD-DFT) calculations, using the CAM-B3LYP functional and DKH2 relativistic Hamiltonian, together with results obtained from calculations using the JOYSpectra platform corroborated the experimental results. Based on these findings, new heteronuclear compounds of lanthanide ions with different carboxylate and β-diketonate ligands present potential for various applications. Editor: Universidade Federal da Paraíba Tipo: Tese

2024-04-29T00:00:00Z Nobrega, Martha Maria Gomes https://repositorio.ufpb.br/jspui/handle/123456789/38247 2026-06-28T06:16:13Z 2025-12-15T00:00:00Z

Título: Estudo do armazenamento, das isotermas de adsorção e aplicação cosmética dos pós de Saccharomyces cerevisiae obtidos por secagem em camada de espuma Autor(es): Nobrega, Martha Maria Gomes Orientador: Cavalcante, Josilene de Assis Abstract: The valorization of agro-industrial by-products represents a fundamental strategy for the development of more sustainable and economically viable production processes. The residual biomass of Saccharomyces cerevisiae, obtained after successive fermentation cycles in cachaça production, exhibits a composition rich in proteins, polysaccharides and minerals, features that make it a material with high biotechnological potential, despite still being commonly discarded by the industry. This study aimed to evaluate the technical feasibility, stability, and cosmetic potential of the powder obtained by foam-mat drying. Moisture adsorption isotherms were determined at 15, 30 and 45 °C, with the Henderson model providing the best fit to the experimental data, yielding type II sigmoidal curves. Thermodynamic analysis revealed that the isosteric heat of sorption (Qst) ranged from 44 to 50 kJ mol−1, indicating strong initial interactions between water molecules and active sites of the matrix. Differential variations in enthalpy (ΔH) and entropy (ΔS) decreased with increasing moisture content, evidencing greater organization of the adsorbed water layers and lower energy required for sorption. Negative Gibbs free energy (ΔG) values confirmed the spontaneity of the process and the affinity of the dried yeast for water. Among the drying conditions evaluated, the central point (60 °C and 10% foaming agent) showed the best performance, resulting in a more stable and less hygroscopic powder, which was selected for the subsequent stages of the study. During 90 days of storage in different packaging materials, under ambient (26 °C/75% RH) and accelerated (40 °C/75% RH) conditions, storage time was the most influential factor, followed by temperature and packaging type. Increased time and temperature intensified moisture gain and color variations, while high-density polyethylene (HDPE) packaging provided the best water-vapor barrier, preserving physicochemical properties for longer periods. Shelf life was estimated using kinetic modeling based on the Arrhenius equation, considering water activity and moisture content as critical parameters. The material packaged in HDPE and stored under ambient conditions showed the longest stability, with a shelf life of 12 months. In addition, the powder obtained under the central-point condition was incorporated into a cosmetic facial cream formulation, which exhibited a homogeneous appearance and no phase separation. Rheological analysis indicated pseudoplastic behavior well described by the Herschel–Bulkley model, demonstrating good structural stability. The presence of the active ingredient acted as a rheological modulator, reducing rigidity and improving flow, which resulted in greater spreadability and superior sensory performance compared with the control formulation. These results confirm that foam-mat drying is a viable and efficient technique for producing Saccharomyces cerevisiae powders with adequate stability and strong potential for application in sustainable cosmetic products. Editor: Universidade Federal da Paraíba Tipo: Dissertação

2025-12-15T00:00:00Z