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51.
Luisa Célia Melo Djenaine De Souza Pedro de Lima‐Neto Adriana Nunes Correia 《Electroanalysis》2010,22(21):2502-2510
The highly boron‐doped diamond electrode (HBDD) combined with square wave voltammetry (SWV) was used in the development of an analytical procedure for diquat determination in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices. Preliminary experiments realised in a medium of 0.05 mol L?1 Na2B4O7 showed the presence of two voltammetric peaks around ?0.6 V and around ?1.0 V vs. Ag/AgCl/Cl? 3.0 mol L?1, where the first peak could be successfully used for analytical proposes due the facility in the electrode surface renovation. After the experimental and voltammetric optimisation, the calculated detection and quantification limits were 1.6×10?10 mol L?1 and 5.3×10?10 mol L?1 (0.057 µg L?1 and 0.192 µg L?1, respectively), which are lower than the maximum residue limit established for fresh food samples by the Brazilian Sanitary Vigilance Agency. The proposed methodology was used to determine diquat residues in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices and the calculated recovery efficiencies indicated that the proposed procedure presents higher robustness, stability and sensitivity, good reproducibility, and is very adequate for diquat determination in complex samples. 相似文献
52.
da Silva JN Salcedo E de Oliveira AB Barbosa MC 《The Journal of chemical physics》2010,133(24):244506
Using molecular dynamic simulations, we study a system of particles interacting through a continuous core-softened potentials consisting of a hard core, a shoulder at closest distances, and an attractive well at further distance. We obtain the pressure-temperature phase diagram of this system for various depths of the tunable attractive well. Since this is a two length scale potential, density, diffusion, and structural anomalies are expected. We show that the effect of increasing the attractive interaction between the molecules is to shrink the region in pressure in which the density and the diffusion anomalies are present. If the attractive forces are too strong, particle will be predominantly in one of the two length scales and no density of diffusion anomaly is observed. The structural anomalous region is present for all the cases. 相似文献
53.
Paula Santos Nunes Marília Santos Bezerra L. P. Costa Juliana Cordeiro Cardoso R. L. C. AlbuquerqueJr. M. O. Rodrigues Gabriela Borin Barin Francilene Amaral da Silva A. A. S. Araújo 《Journal of Thermal Analysis and Calorimetry》2010,99(3):1011-1014
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film. 相似文献
54.
J. Canotilho R. A. E. Castro M. T. S. Rosado S. C. C. Nunes M. S. C. Cruz J. S. Redinha 《Journal of Thermal Analysis and Calorimetry》2010,99(2):423-429
The growth of atenolol, pindolol and betaxolol hydrochloride from melt was investigated by differential scanning calorimetry
(DSC) and polarized light thermal microscopy (PLTM). Phase transitions occurring on cooling and subsequent reheating runs
performed between −160 °C and a temperature above the respective melting points were studied by DSC. The thermal cycles were
also followed by PLTM. Details about the dynamic of the crystallization front taken from microscopic observations are given.
An explanation of the results on the basis of molecular supramolecular recognition is advanced. 相似文献
55.
56.
Hernane T. Barcelos Luclecia D. Nunes Guilherme W. Tavares Edesio F. C. Alcantara Alexandre G. S. Prado 《Journal of Thermal Analysis and Calorimetry》2011,106(2):421-425
Silica gel was modified by silanization reaction followed by functionalization of histamine in a heterogeneous route. These
materials were characterized by elementary nitrogen and chloride analyses, porosity, thermogravimetry, and infrared. The functionalized
surface adsorbed Cu(II), Co(II), Ni(II), and Zn(II) ions in an aqueous solution at 25 °C. The isotherms of adsorption are
in accordance with Langmuir model and the surface presented a great potential to form complexes metal-surface in the chemical
reason of 1:1. 相似文献
57.
Adriana Lídia Santana Cristiano Giacomelli Paula Nunes Oliveira Alfredo Tibúrcio Nunes Pires José Roberto Bertolino Almir Spinelli 《Journal of Polymer Science.Polymer Physics》2009,47(2):215-225
The effect of poly(2‐vinyl pyridine) (P2VP) and poly(4‐vinyl pyridine) (P4VP) isomers on the growth of surface films on copper substrates was studied by electrochemical, spectroscopic, thermogravimentric, and microscopic methods. In acid environment (3% v/v acetic acid) and in the presence of KSCN, electrochemically generated copper cations reacted rapidly with SCN? and P2VP or P4VP, yielding coordination compounds, which deposited onto copper surfaces as films. The characteristics of such polymer–metal complexes (films) were markedly isomer‐dependent. Cu(I)/P2VP/SCN? complexes with monovalent cations and sulfur‐coordinated thiocyanate were obtained in the presence of P2VP, whereas the formation of Cu(II)/P4VP/SCN? complexes with divalent cations and nitrogen‐coordinated thiocyanate was observed in the presence of P4VP. Interestingly, similar physical–chemical properties (electronic structure, stoichiometry, and thermal behavior) were observed for materials synthesized by electrochemical and chemical methods. These results suggest, therefore, that control over the surface properties of copper substrates can be achieved using electrosynthesized films based on different PVP isomers. Besides acting as effective protective barriers against aggressive media and thus reducing the metal dissolution (corrosion) kinetics, these materials are potentially attractive for other applications in which surface properties are paramount, such as in catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 215–225, 2009 相似文献
58.
59.
Sandra S. Ferreira Dário Ferreira Célia Nunes João T. Mexia 《Mathematical Methods in the Applied Sciences》2023,46(1):356-367
Sub-models of mixed linear models are considered. The independence of these sub-models leads to sufficient statistics for the parameters relevant for their densities. Using pivot variables, confidence regions are obtained as well hypothesis testing for variance components, estimable functions, and estimable vectors. In addition, to compare the estimators and the models, we present the histograms with the empirical joint densities for positive and negative parts of the estimators. The figures, for the two-dimensional charts, contain the corresponding UMVUE and are all unimodal with the UMVUE near the mode. The nearness of the estimators and the modes validates the presented methodology and allows the safe use of induced densities. A numerical example applied to real data is presented. 相似文献
60.
Bruno Fernandes Ana C. Correia Fernanda Cosme Fernando M. Nunes 《Natural product research》2015,29(1):37-45
The purpose of this work was to study the volatile composition of vine leaves and vine leaf infusion prepared from vine leaves collected at 30 and 60 days after grape harvest of two Vitis vinifera L. species. Eighteen volatile compounds were identified by gas chromatography–mass spectrometry in vine leaves and in vine leaf infusions. It was observed that the volatile compounds present in vine leaves are dependent on the time of harvest, with benzaldehyde being the major volatile present in vine leaves collected at 30 days after harvesting. There are significant differences in the volatile composition of the leaves from the two grape cultivars, especially in the sample collected at 60 days after grape harvest. This is not reflected in the volatile composition of the vine leaf infusion made from this two cultivars, the more important being the harvesting date for the volatile profile of vine leaf infusion than the vine leaves grape cultivar. 相似文献