Full text
| |
| Author(s): |
Phabyanno Rodrigues Lima
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Química |
| Defense date: | 2009-07-16 |
| Examining board members: |
Lauro Tatsuo Kubota;
Zeki Naal;
Maria Del Pilar Taboada Sotomayor;
André Luiz Barboza Formiga;
José Alberto Fracassi da Silva
|
| Advisor: | Lauro Tatsuo Kubota; Marilia Oliveira Fonseca Goulart |
| Abstract | |
In this work, the development of amperometric sensors based on a simple carbon paste electrode modified with a new redox ¿mediator¿, 4- nitrophthalonitrile (4-NO2PH), for quantification of some antioxidants of biological relevance (L-cystein (L-CySH), L-glutathione (L-GSH), L-ascorbic acid (L-AscH2), uric acid (UA) and b-nicotinamide adenine dinucleotide (NADH)), is described. For this purpose, initially, 4-NO2PH was activated in situ, generating a stable redox-active nitroso/hydroxylamine system (4- NOPH/4-NHOHPH) on the electrodic surface, which presented electrocatalytic activity towards the oxidation of studied analytes. The techniques used in this work were cyclic voltammetry and cronoamperometry, to study the behavior of the modified electrodes, for the experimental parameters optimization, for the attainment of the kinetic parameters and analytical characterization of the sensors. Hydrodynamic and cronoamperometric studies were carried out with the aim to get information on the reduction processes and oxidation of L-AscH2 and NADH, respectively, on the modified electrodes. Through the Koutech-Levich and Cotrell plots it was possible to obtain the values for the diffusion coefficient (D) and kinetic constant of the reaction (kobs) for the analytes in study. The values of the diffusion coefficient and kobs, determined for L-AscH2 and NADH were 9,0x10 cm s and 2,4x10 cms, 6,0x10 molL s and 1,0x10 molL s, respectively. The increase of the reaction rate for L-AscH2 and NADH was attributed to the efficient electron transfer between the studied species and immobilized electroactive species on the surface of the carbon paste electrode. After optimizing conditions, the sensor provided a linear response range (mmol L), limit of detection (LOD) (mmol L), limit of quantification (LOQ) (mmol L) and sensitivity (nA L mmol) for L-CySH (a), L-GSH (b), L-AscH2 (c), UA (d) e NADH (e) of (a) 0.8-13.2, 0.25, 0.8, 37.0; (b) 8.0-83.0, 2.7, 8.0, 54.0; (c)5.0-120.0, 1.6, 5.5, 108.0; (d) 5.0-120.0, 1.3, 4.5, 121.6 and (e) 0.8- 8.5, 0.25, 0.82, 500.0, respectively. After the application of these sensors in samples of interest, studies of addition and recovery of the analytes were carried out to evaluate the error of the methods and it was verified recovery percentages between 98.5 and 102.0% for L-CySH, L-GSH, L-AscH2 and AU, were obtained (AU) | |