Authors:P. Oropesa, A. Hernández, and R. Gutiérrez
The establishment of a quality management system is the best way to comply with international requirements concerning the achievement of confident and traceable analytical results. Some important points dealing with the technical factors of quality management in gamma-ray spectrometry of environmental samples are discussed. The experience obtained from analytical procedure validation is presented. Results of the application of standardized procedures to the analysis of ALMERA intercomparison samples, as well as the outcome of the utilization of certified reference materials for the quality control of measurement are presented. In fact, the implantation of simple technical principles reports reliable results and allows to elevate the quality of the measurements at a cost relatively low according to the real possibilities of the small laboratories, even in developing countries.
The method of thermodielectrical analysis registers in its thermogram a low temperature effect (50–350°) related with the polarization of water or other sorbed phase and cationic polarization, and a high temperature effect (400–900°) which is fundamentally related with cationic conduction. In the present report with the help of the measurement of the dielectrical permittivity of powders of homoionic zeolites was shown the role of cationic polarization in the determination of the intensity of the first thermal effect registered in thermodielectrical analysis.
Authors:A. Rodríguez, R. Hernández, R. Ma. García, and L. Macías
The decomposition of AU, UO3, and U3O8 has been studied at different heating rates and calcining temperatures at atmospheric pressure with pure carbon monoxide, in the temperature range of 350 to 1000°C. X-ray powder patterns and infrared analysis of samples revealed that the final products depend upon the nature of the precursor and its thermal treatment.
Authors:L. Desdín, R. Pérez, J. Miranda, and A. Hernández
The neutron reflection method was applied for the determination of the bound water content and its spread in lateritic mineral. The aim of the work was to study the influence of bound water on the accuracy of the moisture measurement. The distribution of bound water in the mineral can be described by a normal Gaussian curve.
Authors:J. M. Zaldívar, H. Hernández, C. Barcons, and R. Nomen
Although the heat produced by aromatic nitration is relatively large in comparison to the heat produced by dilution, knowledge of the rate of heat generation due to dilution of the mixed acid is important for predicting the dynamic behaviour of discontinuous nitration processes. In this paper a mathematical model, its implementation and experimental validation of the heat effects due to dilution are described and discussed.
Authors:R. García-Estepa, B. García-Villanova, E. Guera-Hernández, and J. Contreras-Calderón
In Spain the consumption of bakery products is increasing, while that of bread is decreasing. Baked goods have a high fat and sugar content, and their intake accounts for a high percentage of the food consumed by the population for breakfast, mid-morning and mid-afternoon meals. Twenty products, with and without cream and chocolate, were analysed. The nutrients examined were proteins, fats and fatty acids, carbohydrates, sugars, starch, and fibre. The values for carbohydrates ranged between 36.8% and 62.3%, and for sugars between 9.0% and 33.8%. The fat content ranged from 6.0% to 36.8%, while 76% of the saturated fatty acids (SFA) determined were atherogenic acids. In accordance with daily energy intake recommendations for SFA and sugars, the intake of one serving of the product provides 25% or more of the recommended energy from SFA for nine of the twenty baked goods tested, and more than 15% of the energy recommended from sugars for fourteen of these products.
Authors:R. Casañas Rivero, P. Suárez Hernández, E. Rodríguez Rodríguez, and C. Díaz Romero
Moisture, protein, starch, amylose, ash, ascorbic acid and fibre contents were determined in potato samples harvested in Tenerife belonging to eight cultivars and three species/subspecies:
chaucha, Solanum tuberosum
. There were several significant differences among the means of various chemical compounds according to cultivar, species or subspecies, local and recently imported potatoes. Mean values of moisture contents were often significantly different concerning the three species/subspecies considered. Local potatoes presented lower moisture and higher content of chemical compounds than the recently imported potatoes. After Varimax rotation, the first component was related to starch, and in a lesser extent to moisture (negatively), the second and the third components were associated to ash. Applying discriminant analysis on potato samples belonging to the spp.
, adequate separation according to the cultivars was obtained.
Authors:B. Zeifert, J. Salmones, J. Hernández, R. Reynoso, N. Nava, E. Reguera, J. Cabañas-Moreno, and G. Aguilar-Ríos
Rancy type catalysts were prepared by means of a two step procedure: (1) Mechanical alloying of the metals and, (2) alkaline aluminum leaching. Mechanical alloying is a novel atlernative related to the synthesis of skeletal Ni catalysts. X-ray diffraction, and Mössbauer spectroscopies were performed for catalysts characterization. Binary Al-Ni and ternary Al-Ni-Fe alloys were produced by mechanical alloying from pure metallic powders; in particular, the intermetallic -(AlNi) phase was formed with a fine microstructure as a non-equilibrium phase; then, aluminum was selectively removed. After aluminum leaching the -(AlNi) phase was transformed into the more stable nickel fee structure.
Authors:F. J. Lona-Ramírez, R. Herrera-Muñoz, V. Rico-Ramírez, F. Louvier Hernández, G. Luna-Bárcenas, and G. González-Alatorre
Although the product resulting from the nitrosation of 1,1,3-trimethylurea is a carcinogenic agent, there have been no kinetic studies reported on such a reaction. This work determines the kinetic parameters and the corresponding reaction mechanism.