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Accurate determinations of the platinum group elements (PGEs) and gold, known as the precious metals, have always been difficult tasks. The metals are often present at trace levels in sample types of complex composition. This situation has improved recently due to developments of instrumental methods and their applications to analyses of the precious metals in a variety of matrices. Attention has been given to determinations of traces of precious metals in biological, clinical and environmental samples. Foremost in importance is inductively coupled plasma mass spectrometry (ICP-MS) which has provided a sensitive means of simultaneous determination of traces of PGEs and gold. Important extensions and improvements in atomic absorption spectrometry (AAS), nuclear and electrochemical methods have been reported also. More research on sample treatments, especially fire assays, applied to PGEs has been carried out. Chlorination has proven to be a viable alternative to fire assays for preconcentration of PGEs and gold in analyses of geological materials. In addition, the recent availability of some additional reference materials will be of great assistance in research work on precious metals. 相似文献
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A. S. Tompa R. D. Barefoot E. Price 《Journal of polymer science. Part A, Polymer chemistry》1968,6(10):2785-2794
Nuclear magnetic resonance relaxation and line width studies were performed on two carboxyl-terminated polybutadiene polymers and their corresponding binders at temperatures from ?170 to 25°C. It was observed that the line widths of the binders increased as the functionality of the corresponding liquid polymers increased. In addition, glass transition temperatures and activation energies obtained from line width measurements were determined. From pulse measurements the magnitude of the relaxation time T1 and the temperature at which T1 is a minimum were determined for a polymer and its corresponding binder. These empirical quantities for the carboxyl-terminated polybutadiene polymers were lower than those of the corresponding binders because of less restraints in the internal motions of the polymer chain. 相似文献
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The direct introduction of solid samples (air filters) to the inductively coupled plasma source of an atomic emission spectrometer using a furnace atomizer has been studied. Conditions have been found for the analysis of elements which volatilize with varyling degrees of difficulty. Lead, copper and vandaium compounds retained on glass fibre filters from air pollution studies have been determined. The results are in good agreement with those obtained by means of established sample dissolution/atomic emision methods. 相似文献
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Juliana S Luz Celso RR Ramos Márcia CT Santos Patricia P Coltri Fernando L Palhano Debora Foguel Nilson IT Zanchin Carla C Oliveira 《BMC biochemistry》2010,11(1):22
Background
The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors. 相似文献6.
R. R. Barefoot 《Trends in analytical chemistry : TRAC》1999,18(11):42-707
The use of platinum group elements (PGEs) as components of autocatalytic converters attached to motor vehicles has resulted in serious contamination of the environment by Pt, Rh and Pd in nanocrystalline forms. Trace concentrations of PGEs, particularly the major component Pt, in environmental samples have been measured by sensitive instrumental procedures. These data have raised further questions about the nature of Pt species in contaminated soils and in plants grown in them. The focus of attention is changing from accumulations of data expressing total concentrations to investigations of speciation. Application of analytical procedures for research on speciation has provided information concerning transformations of Pt compounds in contaminated soils, the uptake of Pt by plants and the nature of Pt compounds in vegetation. Determination of background levels of precious metals in clinical and environmental matrices has required the development of analytical methods which combine uses of minimal quantities of reagents, and as small a number of chemical operations as possible to yield very low procedural blanks. Sensitive instrumental methods based upon high resolution inductively coupled plasma mass spectrometry and adsorptive stripping voltammetry have proven to be valuable for this work. 相似文献
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Renata Monteiro-Maia Maria B Ortigão-de-Sampaio Rosa T Pinho Luiz RR Castello-Branco 《Journal of immune based therapies and vaccines》2006,4(1):1-6
We hypothesize that the energy strategy of a cell is a key factor for determining how, or if, the immune system interacts
with that cell. Cells have a limited number of metabolic states, in part, depending on the type of fuels the cell consumes.
Cellular fuels include glucose (carbohydrates), lipids (fats), and proteins. We propose that the cell's ability to switch
to, and efficiently use, fat for fuel confers immune privilege. Additionally, because uncoupling proteins are involved in
the fat burning process and reportedly in protection from free radicals, we hypothesize that uncoupling proteins play an important
role in immune privilege. Thus, changes in metabolism (caused by oxidative stresses, fuel availability, age, hormones, radiation,
or drugs) will dictate and initiate changes in immune recognition and in the nature of the immune response. This has profound
implications for controlling the symptoms of autoimmune diseases, for preventing graft rejection, and for targeting tumor
cells for destruction. 相似文献
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A liquid membrane containing 4% di-2-ethylhexyl phosphoric acid and 5% sorbitan monooleate in kerosene is used in the form of an emulsion for the simultaneous extraction and concentration of cadmium and manganese from aqueous solutions. When 4% tri-n-octylamine is included in the membrane composition, only manganese is extracted while cadmium remains in the sample solution. The extracted elements in the concentrate are recovered by breaking the emulsion with n-butanol. Recoveries of cadmium and manganese range from 92-104% for 60-ml samples containing 2-9 mug of each element. 相似文献
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Let G be a graph of order n with exactly one Hamiltonian cycle and suppose that G is maximal with respect to this property. We determine the minimum number of edges G can have. 相似文献