Navegando por Palavras-chave "Espectroscopia De Impedância Eletroquímica"

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    Eletrodos de ouro modificados com monocamadas auto-organizadas aplicados à determinação eletroanalítica de hormônios
    (Universidade Federal de São Paulo (UNIFESP), 2020-06-04) Batista, Fabio Henrique Ferreira [UNIFESP]; Oliveira, Lucia Codognoto de [UNIFESP]; Universidade Federal de São Paulo
    In this work, characterization studies of gold electrodes modified with self-organized monolayers of 3-mercaptopropionic acid (AuMPA) and 2-mercapto-5-methyl-benzimidazole (AuMMB) and their applications in the determination of hormones are presented. The characterization by cyclic voltammetry indicated the immobilization of the monolayer of the MPA thiol on the surface of the gold electrode; the characterization by electrochemical impedance spectroscopy (EIS) showed the increase in charge transfer resistance due to the presence of the monolayer and made it possible to estimate the electrode coverage of the modified electrodes AuMPA and AuMMB in 74.4 e 65.4%, respectively; in the characterization by Raman spectroscopy, the presence of several shifts attributed to the MPA and MMB species was observed, thus showing that the modification of the electrodes was in fact performed. The potential of the modified electrodes was evaluated in the electrochemical study of the hormonal endocrine disruptors estradiol and estrone; pH studies indicated the 1: 1 proton: electron ratio and potential sweep rate studies denoted an electrochemical diffusion-controlled process for both. In the voltammetric study of signal stability, greater peak current stability for hormones was obtained when using the AuMMB electrode after 10 successive voltammograms. After the optimization of the square wave voltammetry parameters, analytical curves for estrone over Au and AuMMB electrodes were obtained, with limits of detection (LOD) and quantification (LOQ) of 1.07x10-6 mol L-1 and 3.57x10-6 mol L-1 (Au); and 1.17x10-6 mol L-1 and 3.90x10-6 mol L-1 (AuMMB) in ultrapure water and limits of detection (LOD) and quantification (LOQ) of 7.53x10-7 mol L-1 and 2.51x10 -6 mol L-1 (Au); and 6.94x10-7 mol L-1 and 2.31x10-6 mol L-1 (AuMMB) in water collected in the Billings dam, respectively. From partition studies in the water/n-octanol system for estrone, logD values ​​were estimated at 1.02 and 1.08 (pH 10.0), and 2.10 and 1.35 (pH 12.0 ) in ultrapure water and water sample from Billings Dam, respectively. Thus, the presence of other organic compounds in the matrix influences the partitioning process and suggests the accumulation of this species in sediments when inserted in quiescent water bodies.