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61.
Vanesa Guillén-Casla María Eugenia León-González Luis Vicente Pérez-Arribas Luis María Polo-Díez 《Analytical and bioanalytical chemistry》2010,397(1):63-75
Changes in free amino acids content and its potential racemization in ready-to-eat foods treated with E-beam irradiation between
1 and 8 kGy for sanitation purposes were studied. A simple heart cut two-dimensional high performance liquid chromatographic
method (LC–LC) for the simultaneous enantiomeric determination of three pairs of amino acids used as markers (tyrosine, phenylalanine,
and tryptophan) is presented. The proposed method involves the use of two chromatographs in an LC–LC achiral–chiral coupling.
Amino acids and their decomposition products were firstly separated in a primary column (C18) using a mixture of ammonium acetate buffer (20 mM, pH 6) (94%) and methanol (6%) as the mobile phase. Then, a portion of
each peak was transferred by heart cutting through a switching valve to a teicoplanin-chiral column. Methanol (90%)/water
(10%) was used as the mobile phase. Ultraviolet detection was at 260 nm. Detection limits were between 0.16 and 3 mg L−1 for each enantiomer. Recoveries were in the range 79–98%. The LC–LC method combined with the proposed sample extraction procedure
is suitable for complex samples; it involves an online cleanup, and it prevents degradation of protein, racemization of L-enantiomers,
and degradation of tryptophan. Under these conditions, D-amino acids were not found in any of the analyzed samples at detection
levels of the proposed method. 相似文献
62.
63.
S. Martínez F. Zinola G. Planes O. Guillén-Villafuerte J. L. Rodríguez E. Pastor 《Journal of Solid State Electrochemistry》2007,11(11):1521-1529
Polymer electrolyte fuel cells constitute one of the most important efficiency energy converters for non-centralised uses.
However, the use of fuels arising from reformate processes significantly lowers the current efficiency because of anodic catalytic
poison coming from adsorbed carbon monoxide (COad). In this work, the influence of the addition of hydrogen peroxide in the flow current is studied, considering the adsorption
and electrochemical oxidation of carbon monoxide on carbon-supported Pt (20% Pt/Vulcan) and Pt:Ru (1:1, 20% Pt:Ru/Vulcan)
catalysts in 2 M sulphuric acid. The investigation was conducted applying cyclic voltammetry and on-line differential electrochemical mass spectrometry. A series of experiments has been performed to investigate the influence of
the temperature as well as the time of contact and the concentration of hydrogen peroxide. Oxidation of COad to carbon dioxide occurs at lower potentials in the presence of hydrogen peroxide. Moreover, it is possible to remove ca.
70% of COad on Pt/C electrodes. On the other hand, for PtRu/C electrodes, similar charge values to those of Pt/C electrodes were obtained
for the CO stripping, but the process occurs at more negative potentials. In this case, the effect of partial desorption for
COad by interaction with hydrogen peroxide is added to the bifunctional mechanism usually considered for this alloy.
This paper is dedicated to Prof. Francisco Nart, in memoriam. 相似文献
64.
There is considerable interest in the analysis of phenolic compounds due to their involvement in the organoleptic characteristics of foods and drinks, and their contribution to protection against cardiovascular diseases and cancers through their antioxidant activity. This article describes studies of the polyphenol content, both total (by means of the Folin-Ciocalteu method) and individual (by means of HPLC, LC-MS and LC-MS-MS) and the antioxidant power, of six varieties of grape over the course of their maturation. A good correlation is found to exist between the total polyphenol content of the samples and their antioxidant power, and both seem diminish along the maturation. 相似文献
65.
Summary The retention indices of mono and polycycloolefins with endo or exo double bonds, on squalane or polypropylenglycol 425 are related to their physico-chemical properties such as boiling point, molar volume, molar refraction, and refractive index. Equations have been empirically obtained, from which accurate retention indices of these compounds can be predicted. Unknown boiling points of some of these compounds can also be calculated from their lineal relation with the retention index on squalane. 相似文献
66.
C. Martínez Montero M.C. Rodríguez Dodero D.A. Guillén Sánchez C.G. Barroso 《Chromatographia》2004,59(1-2):15-30
This review presents a study of new advances in chromatographic methods and capillary electrophoresis for the analysis and quantification of carbohydrates in food and drink that have been made in essentially the last seven years (1995–2002). All the main groups of sugars have been considered: monosaccharides, disaccharides, trisaccharides, oligosaccharides, related compounds such as alditols, alditol glycosides, polyols, amino sugars, deoxy sugars, uronic acids and aldonic acids. The chromatographic methods referred to are High Performance Liquid Chromatography (HPLC), Gas Chromatography (GC) and related techniques (AMD-HPTLC: High Performance Thin-Layer Chromatography with Automated Multiple Development). Capillary Electrophoresis (CE) was also discussed. 相似文献
67.
A. Baeza J. Guillén J. W. Mietelski 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(2):375-380
Almost all studies on the radioactive content of mushrooms have been centered on 137Cs and, to a lesser extent, on 40K. Other alpha and beta emitters have not been fully investigated and, therefore, their contribution to the dose due to consumption of mushrooms is not taken into consideration. We have studied the incorporation of several radionuclides: into mushrooms using two approaches — laboratory and natural conditions. Pleurotus eryngii was cultured under controlled laboratory conditions, and was found that 134Cs was incorporated to a greater extent in the mushroom than the rest of radionuclides, and 239Pu at least. These results were confirmed by the uptake under natural conditions: 137Cs > 228,230,232Th 234,238U 90Sr >> 239+240Pu. The contribution of thorium and uranium to the dose due to mushroom consumption in Spain is of the same order of magnitude as that of 137Cs.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
68.
F. Guillén-González 《Czechoslovak Mathematical Journal》2004,54(3):637-656
We study the system of PDEs describing unsteady flows of incompressible fluids with variable density and non-constant viscosity. Indeed, one considers a stress tensor being a nonlinear function of the symmetric velocity gradient, verifying the properties of p-coercivity and (p–1)-growth, for a given parameter p > 1. The existence of Dirichlet weak solutions was obtained in [2], in the cases p 12/5 if d = 3 or p 2 if d = 2, d being the dimension of the domain. In this paper, with help of some new estimates (which lead to point-wise convergence of the velocity gradient), we obtain the existence of space-periodic weak solutions for all p 2. In addition, we obtain regularity properties of weak solutions whenever p 20/9 (if d = 3) or p 2 (if d = 2). Further, some extensions of these results to more general stress tensors or to Dirichlet boundary conditions (with a Newtonian tensor large enough) are obtained. 相似文献
69.
J. L. Miramontes J. Sánchez Guillén 《Zeitschrift fur Physik C Particles and Fields》1988,41(2):247-257
A thorough discussion of perturbative QCD for twist-4 is presented from a practical point of view. Misleading uses of intrinsic transverse momentum and mass terms are criticized and corrected in the complete expressions relevant for a model-independent experimental test of power corrections which is proposed. Upper and lower bounds for the twist-4 scale are deduced from a theoretically-consistent analysis of present DIS data with a simplified assumption on twist-4, from which a power-dominatedR=σ L /R=σ T is predicted. 相似文献
70.
Guillén Esteban Ferrer Amparo Agrisuelas Jerónimo García-Jareño José J. Vicente Francisco 《Journal of Solid State Electrochemistry》2020,24(10):2353-2363
Journal of Solid State Electrochemistry - The study of the first stages of the transformation of conducting films from the insulating to the conducting form by oxidation is essential to understand... 相似文献