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Journal of Thermal Analysis and Calorimetry
Authors: R. Briones-Martínez, M. Juárez-Juárez, M. Oliver-Salvador, and M. Cortés-Vázquez

Abstract  

DSC was used to study the extent of denaturation of hemisphaericin and mexicain hydrolysates from corn gluten, soybean and sunflower meals. It was observed that the defatted meals studied exhibited only one broad peak transition. The data obtained demonstrated that the partial protein denaturation found with hemisphaericin or mexicain is correlated to modifications of functional properties. The two enzymes display different modes of action, according to the protein source.

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Abstract  

Mass Spectrometry has been the usual method to determine Ar concentrations in mineral samples for dating them through the40Ar/40K ratio. This technique has been replaced since 1966 by measurement of40Ar/39Ar ratio, after artificial production of39Ar from the39K(n,p)39Ar reaction produced in the fast neutron flux of a nuclear reactor. This method requires the fusion of the sample by incremental heating until reaching a temperature of 1000°C in order to get the total release of both argon isotopes. In principle, it should be possible to determine the40Ar/40K ratio by activation analysis in an easier, non-destructive way, but it presents the following drawbacks: manufacture of argon standards; usual low ratio peak/Compton distribution for both peaks: 1.29 Mev and 1.52 Mev (41Ar and42K respectively), since potassium minerals are usually very rich in sodium, manganese and chlorine; reaction41K(n,p)41Ar induced by fast neutrons present in the thermal flux; and possible contamination of the samples and standards with atmospheric40Ar (99.6% of elementary Ar, whose proportion in the atmosphere at sea level is 0.93%). This paper describes how these problems may be solved, also determining the limits of Ar and K concentration related to Compton distribution, in our experimental conditions.

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Abstract  

The preliminary results of indoor radon concentration measurements taken in some of Mexico City’s colonial churches and convents are presented. Measurements were taken in the churches of Santa Catarina, La Conchita, San Juan Bautista, San Antonio Panzacola, San Diego and San Mateo and the church and convent complex of El Carmen. These structures are all located in Coyoacan, a borough of Mexico City. Indoor radon concentrations in churches and convents constructed in the 17th and 18th centuries are interesting for several reasons. Most of these buildings were built using the stones of ancient Mexican pyramids, mainly blocks of basalt and volcanic pyroclastic rocks, and possess walls between 40 cm and 70 cm thick and naves with large volumes of air and relative low ventilation. The churches are public places with people most of the time. The indoor radon concentrations were measured using nuclear track detectors consisting of a closed-end cup containing CR-39 Lantrack® polymer as detector material. The measurements were taken over four periods of three consecutive months. The results show indoor radon concentrations of between 82 and 165 Bq·m−3, below to the United States Environmental Protection Agency (USEPA) indoor radon action level for workplaces. Using these results, the radiological risks were calculated and found to be negligible.

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Summary

A high-performance liquid chromatographic method with diode-array detection (HPLC-DAD) has been developed and validated to establish the fingerprint of Turnera diffusa. Hydroalcoholic extracts were obtained from 19 raw herbal samples collected in different regions of México. Separation was performed on a 150 mm × 3.9 mm (4-μm particle) C18 column, using a gradient of methanol and 0.1% aqueous trifluoroacetic acid as the mobile phase. Chromatograms were recorded at 254 nm. To identify each peak, both retention time and peak spectrum were used. Intraday and interday relative standard deviations were <3% for retention time and <12% for relative areas. Extracts were stable in solution for up to 60 days. Results from a robustness study showed that the amount of ethanol in the mobile phase had a substantial effect on retention time. The relative areas of 12 peaks common to the chromatograms obtained from 19 authenticated T. diffusa samples were chosen to construct a principal-components analysis (PCA) model. The soft independent modeling of class analogy (SIMCA) method based on the PCA model was used to evaluate the quality of eleven commercial products.

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Abstract  

Nine brands of tobacco cigarettes manufactured and distributed in the Mexican market were analyzed by γ-spectrometry to certify their non-artificial radioactive contamination. Since natural occurring radioactive materials (NORM) 40K, 232Th, 235U, and 239U (and decay products from the latter three nuclides) are the main sources for human radiation exposure, the aim of this work was to determine the activity of 40K and potassium concentration. Averages of 40K and potassium concentration were of 1.29±0.18 Bq·g−1, and 4.0±0.57%. The annual dose equivalents to the whole body from ingestion and inhalation of 26 Bq 40K were 0.23 μSv and 15.8 μSv, respectively. The corresponding 50 years committed dose equivalents was 0.23 μSv. The total committed dose to the lungs due to inhalation of 40K in tobacco was 16 μSv. Potassium concentrations obtained in this work were in the same range of those obtained by INAA, so showing that the used technique is acute, reproducible, and accessible to laboratories equipped with low background scintillation detectors.

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