共查询到20条相似文献,搜索用时 15 毫秒
1.
Jon R. Garrison Daniel E. Hanson Howard L. Hall 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(3):885-894
Nuclear forensic science has become increasingly important for global nuclear security, and enhancing the timeliness of forensic
analysis has been established as an important objective in the field. New, faster techniques must be developed to meet this
objective. Current approaches for the analysis of minor actinides, fission products, and fuel-specific materials require time-consuming
chemical separation coupled with measurement through either nuclear counting or mass spectrometry. These very sensitive measurement
techniques can be hindered by impurities or incomplete separation in even the most painstaking chemical separations. High-temperature
gas-phase separation or thermochromatography has been used in the past for the rapid separations in the study of newly created
elements and as a basis for chemical classification of that element. This work examines the potential for rapid separation
of gaseous species to be applied in nuclear forensic investigations. Monte Carlo modeling has been used to evaluate the potential
utility of the thermochromatographic separation method, albeit this assessment is necessarily limited due to the lack of available
experimental data for validation. 相似文献
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3.
Tzschucke CC Markert C Bannwarth W Roller S Hebel A Haag R 《Angewandte Chemie (International ed. in English)》2002,41(21):3964-4000
The shift of paradigm in combinatorial chemistry, from large compound libraries (of mixtures) on a small scale towards defined compound libraries where each compound is prepared in an individual well, has stimulated the search for alternative separation approaches. The key to a rapid and efficient synthesis is not only the parallel arrangement of reactions, but simple work-up procedures so as to circumvent time-consuming and laborious purification steps. During the initial development stages of combinatorial synthesis it was believed that rational synthesis of individual compounds could only be achieved by solid-phase strategies. However, there are a number of problems in solid-phase chemistry: most notably there is the need for a suitable linker unit, the limitation of the reaction conditions to certain solvents and reagents, and the heterogeneous reaction conditions. Further disadvantages are: the moderate loading capacities of the polymeric support and the limited stability of the solid support. In the last few years several new separation techniques have been developed. Depending on the chemical problem or the class of compounds to be prepared, one can choose from a whole array of different approaches. Most of these modern separation approaches rely on solution-phase chemistry, even though some of them use solid-phase resins as tools (for example, as scavengers). Several of these separation techniques are based on liquid-liquid phase separation, including ionic liquids, fluorous phases, and supercritical solvents. Besides being benign with respect to their environmental aspects, they also show a number of advantages with respect to the work-up procedures of organic reactions as well as simplicity in the isolation of products. Another set of separation strategies involves polymeric supports (for example, as scavengers or for cyclative cleavage), either as solid phases or as soluble polymeric supports. In contrast to solid-phase resins, soluble polymeric supports allow reactions to be performed under homogeneous conditions, which can be an important factor in catalysis. At the same time, a whole set of techniques has been developed for the separation of these soluble polymeric supports from small target molecules. Finally, miscellaneous separation techniques, such as phase-switchable tags for precipitation by chemical modification or magnetic beads, can accelerate the separation of compounds in a parallel format. 相似文献
4.
A. R. King A. Davies N. Saint N. Pockett 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):1143-1147
Radiochemical separation methods are required for the accurate measurement of radionuclides in complex matrices. To be able to quantify the results after the separation of radionuclides, known amounts of either radioactive tracers or inactive carrier solutions are added at the start of the separation. The added isotopes/elements are then measured at the end of the analysis to calculate the chemical yield for the element or isotope. The chemical yield data is applied to the counting data of the analytes of interest to produce quantified results. Recently, changes have been made to the techniques used to measure chemical yields at the Atomic Weapons Establishment for samples containing fission products. Preliminary development work using wavelength dispersive X-ray fluorescence and inductively coupled plasma–atomic emission spectrometry is discussed, including a comparison of results and evaluation of measurement uncertainty. The use of the techniques to measure fission products in a thermal neutron irradiated uranium sample is described. 相似文献
5.
1 INTRODUCTION Metallacrown has emerged as inorganic host molecules. There has been considerable interest in metallacrown chemistry owing to its potential applications in chemically modified electrodes, anion-selective separation agents, liquid-crystal precursors and magnetic materials[1]. Multidentate ligands which can bridge two metal ions are used to synthesize metallacrowns. The cyclic repetition of the ligand bridging two metal ions generates the macrocyclic metal cluster. In the c… 相似文献
6.
The quantitative separation of Ca and Sr by sonic of the most interesting chemical procedures has been investigated, using radiochemical tracer techniques. It could be shown that no satisfactory separation could be achieved and good results are obtained in some cases by compensation of errors.The results have been used for the development of an isotopic dilution method for the determination of Ca and Sr in mixtures of their salts, Reliable results arc obtained on the semi-micro-scale. 相似文献
7.
Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis. 相似文献
8.
Summary: The chemical composition distribution has been shown to be the most critical and discriminating parameter in understanding the performance of industrial polyolefins with non homogeneous comonomer incorporation. The chemical composition distribution is being analyzed by well known techniques such as temperature rising elution fractionation, TREF, crystallization analysis fractionation, CRYSTAF and crystallization elution fractionation, CEF. These techniques separate according to crystallizability and provide a powerful and predictable separation of components based on the presence of branches, irregularities or tacticity differences, independently of the molar mass. TREF, CRYSTAF and CEF can not be used, however, for the separation of more amorphous resins, and may not always provide the best solution for complex multi-component resins due to the existence of some co-crystallization. The application of high temperature interactive HPLC to polyolefins opened a new route to characterize these types of polymers. The use of solvent gradient HPLC for separation of polyethylene and polypropylene and the developments in HPLC on carbon based columns extended further the application of high temperature HPLC in polyolefins. A new approach has been developed recently using the carbon based column but replacing solvent gradient by a thermal gradient which facilitates the analysis of polyethylene copolymers and provides a powerful tool for the analysis of elastomers. Thermal gradient interaction chromatography (TGIC) is being compared with TREF and CEF with the analysis of model samples. The advantages/disadvantages of each technique are being investigated and discussed. The combination of TGIC and TREF/CEF provides an extended range of separation of polyolefins. 相似文献
9.
Fedotov PS Vanifatova NG Shkinev VM Spivakov BY 《Analytical and bioanalytical chemistry》2011,400(6):1787-1804
Submicron and micron particles present in liquid environmental, biological, and technological samples differ in their dimensions,
shape, mass, chemical composition, and charge. Their properties cannot be reliably studied unless the particles are fractionated.
Synthetic particles applied as components of analytical systems may also need preliminary fractionation and investigation.
The review is focused on the methods for fractionation and characterization of nanoparticles and microparticles in liquid
media, the most representative examples of their application, and the trends in developing novel approaches to the separation
and investigation of particles. Among the separation techniques, the main attention is devoted to membrane filtration, field-flow
fractionation, chromatographic, and capillary electrokinetic methods. Microfluidic systems employing the above-mentioned and
other separation principles and providing a basis for the fabrication of lab-on-chip devices are also examined. Laser light
scattering methods and other physical techniques for the characterization of particles are considered. Special attention is
given to “hyphenated” techniques which enable the separation and characterization of particles to be performed in online modes. 相似文献
10.
Sample preparation turns out to be one of the important procedures in complex sample analysis by affecting the accuracy, selectivity, and sensitivity of analytical results. However, the majority of the conventional sample preparation techniques still suffer from time-consuming and labor-intensive operations. These shortcomings can be addressed by reforming the sample preparation process in a microfluidic manner. Inheriting the advantages of rapid, high efficiency, low consumption, and easy integration, microfluidic sample preparation techniques receive increasing attention, including microfluidic phases separation, microfluidic field-assisted extraction, microfluidic membrane separation, and microfluidic chemical conversion. This review overviews the progress of microfluidic sample preparation techniques in the last 3 years based on more than 100 references, we highlight the implementation of typical sample preparation methods in the formats of microfluidics. Furthermore, the challenges and outlooks of the application of microfluidic sample preparation techniques are discussed. 相似文献
11.
Stephens JR Beveridge JS Williams ME 《Physical chemistry chemical physics : PCCP》2012,14(10):3280-3289
Despite the large body of literature describing the synthesis of magnetic nanoparticles, few analytical tools are commonly used for their purification and analysis. Due to their unique physical and chemical properties, magnetic nanoparticles are appealing candidates for biomedical applications and analytical separations. Yet in the absence of methods for assessing and assuring their purity, the ultimate use of magnetic particles and heterostructures is likely to be limited. In this review, we summarize the separation techniques that have been initially used for this purpose. For magnetic nanoparticles, it is the use of an applied magnetic flux or field gradient that enables separations. Flow based techniques are combined with applied magnetic fields to give methods such as magnetic field flow fractionation and high gradient magnetic separation. Additional techniques have been explored for manipulating particles in microfluidic channels and in mesoporous membranes. Further development of these and new analytical tools for separation and analysis of colloidal particles is critically important to enable the practical use of these, particularly for medicinal purposes. 相似文献
12.
Lszl Szepesy 《Trends in analytical chemistry : TRAC》1985,4(10):258-261
Coal-derived products are extremely complex mixtures and very little information is available on their chemical composition. In order to obtain distinct fractions from coal liquids, a number of different separation techniques have been used. This paper gives a short overview of the general separation procedures with special emphasis on liquid chromatography and high-performance liquid chromatography techniques using various stationary phases and mobile phase systems. 相似文献
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Review of applications of high-field asymmetric waveform ion mobility spectrometry (FAIMS) and differential mobility spectrometry (DMS) 总被引:1,自引:0,他引:1
High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) and Differential Mobility Spectrometry (DMS) harness differences in ion mobility in low and high electric fields to achieve a gas-phase separation of ions at atmospheric pressure. This separation is orthogonal to either chromatographic or mass spectrometric separation, thereby increasing the selectivity and specificity of analysis. The orthogonality of separation, which in some cases may obviate chromatographic separation, can be used to differentiate isomers, to reduce background, to resolve isobaric species, and to improve signal-to-noise ratios by selective ion transmission. This review will focus on the applications of these techniques to the separation of various classes of analytes, including chemical weapons, explosives, biologically active molecules, pharmaceuticals and pollutants. These papers cover the period up to January 2007. 相似文献
15.
《Spectrochimica Acta Part B: Atomic Spectroscopy》1998,53(2):197-211
Speciation of trace elements is a relatively new field and it was in toxicology that the relationship between the chemical form of a metal and its harmful effects was first recognized. The present need for chemical speciation information in biochemistry bioinorganic and clinical chemistry is documented in an attempt to justify the present demand for innovative chemical speciation strategies and analytical technologies.The challenge and complexity of speciation is stressed and three different categories of analytical speciation of increasing analytical difficulty are proposed. Analytical strategies developed so far to try to tackle speciation problems (computational approaches, direct species-specific and hybrid techniques) are reviewed and critically assessed for biological materials. It is indisputable these days that in most cases of real-life analytical speciation we have to resort to the development and use of hybrid techniques combining an adequate separation technique for the species physical separation and an element specific detector such as those based in atomic spectrometry. Examples of such strategies, as developed mainly in the author's laboratory and including chromatographic and non-chromatographic type hybrid strategies coupled to flame, plasma and electrothermal vaporization atomic detectors, are discussed in more detail.Finally, in light of the latest trends observed in this new field, the author attempts to cast a forward look into the foreseeable future of analytical speciation research in biological and biomedical sciences. The urgent plea for quality assurance in non-routine analysis and the concept of using complementary analytical techniques and definitive methods to attack the complexity of chemical speciation in biological systems are particularly highlighted. 相似文献
16.
Ph. Quevauviller 《Journal of chromatography. A》1996,750(1-2):25-33
The awareness of a need for an improved control of environmental contamination levels has led to the development of new hyphenated techniques for the determination of a wide variety of chemical species (e.g., organotins, methyl-mercury, alkyl-lead compounds etc.). These techniques generally involve many analytical steps such as extraction, derivatisation, separation and detection which have to be carried out in such a way that the speciation is not changed during the abalytical process. The need for evaluating the method's performance has led the BCR programme of the European Commission (now Standards, Measurements and Testing programme) to conduct series of interlaboratory studies during the last decade. These projects followed a step-by-step approach for the evaluation of different steps of the analytical methods used, e.g., simple solutions to test the detection, cleaned extract to evaluate the separation, spiked samples to test the extraction and natural samples to evaluate the whole analytical procedures. These collaborative projects allowed most of the sources of errors related to either a technique or a laboratory to be detected and removed. This paper gives an account of discussions of possible errors occurring in speciation analysis and presents examples of technical scrutiny of hyphenated techniques using chromatography as applied to the determination of tributyltin, methyl-mercury and trimethyllead. 相似文献
17.
Due to the lack of a stable technetium isotope, and the high mobility and long half-life, 99Tc is considered to be one of the most important radionuclides in safety assessment of environmental radioactivity as well as nuclear waste management. 99Tc is also an important tracer for oceanographic research due to the high technetium solubility in seawater as TcO4−. A number of analytical methods, using chemical separation combined with radiometric and mass spectrometric measurement techniques, have been developed over the past decades for determination of 99Tc in different environmental samples. This article summarizes and compares recently reported chemical separation procedures and measurement methods for determination of 99Tc. Due to the extremely low concentration of 99Tc in environmental samples, the sample preparation, pre-concentration, chemical separation and purification for removal of the interferences for detection of 99Tc are the most important issues governing the accurate determination of 99Tc. These aspects are discussed in detail in this article. Meanwhile, the different measurement techniques for 99Tc are also compared with respect to advantages and drawbacks. Novel automated analytical methods for rapid determination of 99Tc using solid extraction or ion exchange chromatography for separation of 99Tc, employing flow injection or sequential injection approaches are also discussed. 相似文献
18.
Janos P 《Electrophoresis》2003,24(12-13):1982-1992
The separation of lanthanide and actinide elements belongs to one of the most challenging tasks of the separation science, due to a great similarity in their physical and chemical properties. The electrophoretic separation can be accomplished in the presence of suitable complex-forming agents, from which alpha-hydroxyisobutyric acid (HIBA) has been used most often. In the most effective capillary electrophoretic mode--capillary zone electrophoresis (CZE)--a complete separation of lanthanide ions can be accomplished within a few minutes. Various electrophoretic methods can be relatively easily adopted for the determinations of individual lanthanide elements in certain kinds of technical materials, concentrates, precursors, etc., where the high speed and low costs of analysis characteristics of capillary electrophoresis (CE) may be advantageously exploited. Electrophoretic techniques may also be employed for speciation studies, especially for examinations of the behavior of actinides in the environment. 相似文献
19.
G. Skarnemark 《Journal of Radioanalytical and Nuclear Chemistry》2000,243(1):219-225
Durung the second half of the 20th century solvent extraction, i.e., the partition of a species between two immiscible phases, has become one of the major techniques for separation of short-lived radionuclides from complex nuclear reaction product mixtures. It is used in nuclear spectroscopy as well as to study chemical properties of the heaviest elements. Here three of the most successful techniques will be presented. Two of them are automatized batch techniques and the third one is fully continuous. Possible future developments will be discussed, especially with respect to continuous solvent extraction. 相似文献
20.
D. E. Hanson J. R. Garrison H. L. Hall 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(1):213-223
Nuclear forensic science has become increasingly important for global nuclear security. However, many current laboratory analysis
techniques are based on methods developed without the imperative for timely analysis that underlies the post-detonation forensics
mission requirements. Current analysis of actinides, fission products, and fuel-specific materials requires time-consuming
chemical separation coupled with nuclear counting or mass spectrometry. High-temperature gas-phase separations have been used
in the past for the rapid separation of newly created elements/isotopes and as a basis for chemical classification of that
element. We are assessing the utility of this method for rapid separation in the gas-phase to accelerate the separations of
radioisotopes germane to post-detonation nuclear forensic investigations. The existing state of the art for thermochromatographic
separations, and its applicability to nuclear forensics, will be reviewed. 相似文献