Percorrer por autor "Fernandes, Diana M."
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- MnFe2O4@CNT-N as novel electrochemical nanosensor for determination of caffeine, acetaminophen and ascorbic acidPublication . Fernandes, Diana M.; Silva, Nádia; Pereira, Clara; Moura, Cosme; Magalhães, Júlia M.C.S.; Bachiller-Baeza, Belén; Rodríguez-Ramos, Inmaculada; Guerrero-Ruiz, Antonio; Delerue-Matos, Cristina; Freire, CristinaFor the first time, a glassy carbon electrode (GCE) modified with novel N-doped carbon nanotubes (CNT-N) functionalized with MnFe2O4 nanoparticles (MnFe2O4@CNT-N) has been prepared and applied for the electrochemical determination of caffeine (CF), acetaminophen (AC) and ascorbic acid (AA). The electrochemical behaviour of CF, AC and AA on the bare GCE, CNT-N/GCE and MnFe2O4@CNT-N/GCE were carefully investigated using cyclic voltammetry (CV) and square-wave voltammetry (SWV). Compared to bare GCE and CNT-N modified electrode, the MnFe2O4@CNT-N modified electrode can remarkably improve the electrocatalytic activity towards the oxidation of CF, AC and AA with an increase in the anodic peak currents of 52%, 50% and 55%, respectively. Also, the SWV anodic peaks of these molecules could be distinguished from each other at the MnFe2O4@CNT-N modified electrode with enhanced oxidation currents. The linear response ranges for the square wave voltammetric determination of CF, AC and AA were 1.0 × 10−6 to 1.1 × 10−3 mol dm−3, 1.0 × 10−6 to 1.0 × 10−3 mol dm−3 and 2.0 × 10−6 to 1.0 × 10−4 mol dm−3 with detection limit (S/N = 3) of 0.83 × 10−6, 0.83 × 10−6 and 1.8 × 10−6 mol dm−3, respectively. The sensitivity values at the MnFe2O4@CNT-N/GCE for the individual determination of AC, AA and CF and in the presence of the other molecules showed that the quantification of AA and CF show no interferences from the other molecules; however, AA and CF interfered in the determination of AC, with the latter molecule showing the strongest interference. Nevertheless, the obtained results show that MnFe2O4@CNT-N composite material acted as an efficient electrochemical sensor towards the selected biomolecules.
- PMo11V@N-CNT electrochemical properties and its application as electrochemical sensor for determination of acetaminophenPublication . Fernandes, Diana M.; Nunes, Marta; Bachiller-Baeza, Belén; Rodríguez-Ramos, Inmaculada; Guerrero-Ruiz, Antonio; Delerue-Matos, Cristina; Freire, CristinaA polyoxometalate-nanocarbon composite, PMo11V@N-CNT, was prepared by a simple procedure which consisted of the immobilization of phosphovanadomolybdate (PMo11V) onto N-doped carbon nanotubes (N-CNT). The FTIR and XPS characterizations confirmed its successful synthesis. The cyclic voltammograms of glassy carbon electrode (GCE) modified with PMo11V and PMo11V@N-CNT showed four Mo-centred redox processes (MoVI/V) and a vanadium redox process (VV/IV). All were surface-confined redox processes. Additionally, PMo11V@N-CNT/GCE showed good stability and well-resolved redox peaks with high current intensities. The electrocatalytic sensing properties of PMo11V@N-CNT/GCE towards acetaminophen (AC) in the presence of tryptophan (TRP) were evaluated by square wave voltammetry. Under the conditions used, the peak current increased linearly with AC concentration in the presence of TRP, with a linear range from 1.5 × 10−6 to 3.9 × 10−4 mol dm−3 and a detection limit of 1.0 × 10−6 mol dm−3.
- Voltammetric analysis of mancozeb and its degradation product ethylenethioureaPublication . López-Fernández, Olalla; Barroso, M. Fátima; Fernandes, Diana M.; Rial-Otero, Raquel; Simal-Gándara, Jesús; Morais, Simone; Nouws, Henri P.A.; Freire, Cristina; Delerue-Matos, CristinaThe purpose of this work was to develop a reliable alternative method for the determination of the dithiocarbamate pesticide mancozeb (MCZ) in formulations. Furthermore, a method for the analysis of MCZ's major degradation product, ethylenethiourea (ETU), was also proposed. Cyclic voltammetry was used to characterize the electrochemical behavior of MCZ and ETU, and square-wave adsorptive stripping voltammetry (SWAdSV) was employed for MCZ quantification in commercial formulations. It was found that both MCZ and ETU are irreversibly reduced (− 0.6 V and − 0.5 V vs Ag/AgCl, respectively) at the surface of a glassy carbon electrode in a mainly diffusion-controlled process, presenting maximum peak current intensities at pH 7.0 (in phosphate buffered saline electrolyte). Several parameters of the SWAdSV technique were optimized and linear relationships between concentration and peak current intensity were established between 10–90 μmol L− 1 and 10–110 μmol L− 1 for MCZ and ETU, respectively. The limits of detection were 7.0 μmol L− 1 for MCZ and 7.8 μmol L− 1 for ETU. The optimized method for MCZ was successfully applied to the quantification of this pesticide in two commercial formulations. The developed procedures provided accurate and precise results and could be interesting alternatives to the established methods for quality control of the studied products, as well as for analysis of MCZ and ETU in environmental samples.