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911.
Francisco Fernandes Gambarra-Neto Mário César Ugulino Araújo Roberto Kawakami Harrop Galvão Everaldo Paulo de Medeiros 《Talanta》2009,77(5):1660-204
This paper proposes a simple and non-expensive electroanalytical methodology for classification of edible vegetable oils with respect to type (canola, sunflower, corn and soybean) and conservation state (expired and non-expired shelf life). The proposed methodology employs an alcoholic extraction procedure followed by square wave voltammetry (SWV). Two chemometric methods were compared for classification of the resulting voltammograms, namely Soft Independent Modelling of Class Analogy (SIMCA) and Linear Discriminant Analysis (LDA) with variable selection by the Successive Projections Algorithm (SPA). The results were evaluated in terms of errors in a set of samples not included in the modelling process. The best results were obtained with the SPA-LDA method, which correctly classified all samples in terms of type and conservation state. 相似文献
912.
A biosensor based on the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate containing dispersed iridium nanoparticles (Ir-BMI.PF6) and polyphenol oxidase was constructed. This enzyme was obtained from the sugar apple (Annona squamosa), immobilized in chitosan ionically crosslinked with oxalate. The biosensor was used for determination of chlorogenic acid by square wave voltammetry. The polyphenol oxidase catalyzes the oxidation of chlorogenic acid to the corresponding o-quinone, which is electrochemically reduced back to this substance at +0.25 V vs. Ag/AgCl. Under optimized operational conditions the chlorogenic acid concentration was linear in the range of 3.48 × 10−6 to 4.95 × 10−5 mol L−1 with a detection limit of 9.15 × 10−7 mol L−1. The biosensor was applied in the determination of chlorogenic acid in organic and decaffeinated coffee and the results compared with those obtained using the capillary electrophoresis method. The recovery study for chlorogenic acid in these samples gave values of 93.2-105.7%. 相似文献
913.
Inga Cikotiene Visvaldas Kairys Rita Buksnaitiene Marius Morkunas Simonas Rudys Algirdas Brukstus Miguel X. Fernandes 《Tetrahedron》2009,65(29-30):5752-5759
Thermal and microwave initiated cyclization of 2,4-disubstituted 6-arylethynylpyrimidine-5-carbaldehydes with tert-butylamine has been studied. A novel high-yielding preparation of 2,4-disubstituted 7-arylpyrido[4,3-d]pyrimidines has been developed. The intermediate compounds were isolated and possible mechanism of the reactions is discussed. 相似文献
914.
Falkoski DL Guimarães VM de Queiroz MV de Araújo EF de Almeida MN de Barros EG de Rezende ST 《Applied biochemistry and biotechnology》2009,158(3):540-551
Partially purified α-Galactosidase from Penicillium griseoroseum was immobilized onto modified silica using glutaraldehyde linkages. The effective activity of immobilized enzyme was 33%.
Free and immobilized α-galactosidase showed optimal activity at 45 °C and pH values of 5 and 4, respectively. Immobilized
α-galactosidase was more stable at higher temperatures and pH values. Immobilized α-galactosidase from P. griseoroseum maintained 100% activity after 24 h of incubation at 40 °C, while free enzyme showed only 32% activity under the same incubation
conditions. Defatted soybean flour was treated with free and immobilized α-galactosidase in batch reactors. After 8 h of incubation,
stachyose was completely hydrolyzed in both treatments. After 8 h of incubation, 39% and 70% of raffinose was hydrolyzed with
free and immobilized α-galactosidase respectively. Immobilized α-galactosidase was reutilized eight times without any decrease
in its activity. 相似文献
915.
P. G. Fernandes P. M. Carreira D. Nunes 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(1):157-160
The Aveiro region, situated on the Northwest coast of Portugal is one of the most industrialized areas of Portugal. The shallow
Quaternary aquifer system, mainly of detrital sediments of Pleistocene and Holocene ages, is still today an important water
resource for this region despite growing evidence of diffuse pollution problems. Isotope techniques have been used to evaluate
the aquifer vulnerability to nitrate contamination (δ18O and δ15N from NO3 and δ2H and δ18O from H2O). Nitrogen isotopes were used to identify nitrogen sources and assess agriculture, cattle-breeding, urban and industrial
contributions to the nitrogen cycle in the Aveiro ecosystem. 相似文献
916.
Felipe Yamada Fonseca Elisabete A. De Nadai Fernandes Vanessa Santos Rodrigues Isabel Pires de Oliveira Cavalca Leandro Camilli Claudiney BardiniJr. Elvis Joacir De França 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(1):117-123
The quality of environmental studies depends on the utilization of adequate sampling protocol and analytical method for obtaining
reliable results and minimizing analytical uncertainties. In order to demonstrate the applicability of INAA for determining
chemical element composition of invertebrates, this work evaluated sample representativeness in terms of subsampling and sample
size. Br, Co, Fe, K, Na, Sc and Zn could be determined in very small samples despite increasing of analytical uncertainties.
Special attention should be directed to invertebrate species with small structures because of the high chemical variation
observed among different sample sizes tested. 相似文献
917.
A. A. R. Fernandes C. A. Ramos A. Macedo Teixeira E. E. Fullerton 《Physica B: Condensed Matter》2002,320(1-4):175-177
We report the temperature dependence of the saturation magnetization, Ms(T), of Fe(t)/Cr(40 Å) superlattices grown on MgO(1 0 0) and MgO(1 1 0) and its variation with Fe-layer thickness (5 Å<t<80 Å). The structure was characterized by X-ray diffraction. Ms(t) vs. T, as measured by DC magnetization and ferromagnetic resonance, show a large interface effect. The origins of this effect are discussed. 相似文献
918.
919.
Fernandes MA Lappert MF Layh M Omondi B 《Chemical communications (Cambridge, England)》2003,(5):656-657
The reaction of LiCH(TMS)2 with phenyl isocyanide PhNC has unexpectedly led to the N-lithio-indole derivative 1, that has been fully characterised including its X-ray crystal structure determination. 相似文献
920.
We introduce two algebraic completely integrable analogues of the Mumford systems which we call hyperelliptic Prym systems,
because every hyperelliptic Prym variety appears as a fiber of their momentum map. As an application we show that the
general fiber of the momentum map of the periodic Volterra lattice
is an affine part of a hyperelliptic Prym variety, obtained by removing n translates of the theta divisor, and we conclude that this integrable system is algebraic completely integrable.
Received: 12 December 2000 / Accepted: 26 March 2001 相似文献