摘要:

One of the major difficulties associated with the chemical separation usually required in activation analysis for trace elements has been the need to determine the chemical yield of the separation process. In a separation using the substoichiometric principle, equal amounts of a reagent capable of converting the irradiated element and its isotopic carrier to an easily-separable form are added to the prepared sample and to the standard, but the reagent is sufficient to react with only a part of the element and carrier which is present. By this means the specific activities of the extracts or precipitates are made proportional to the total activities, and the determination of the absolute chemical yield of the separation is rendered unnecessary. Furthermore, the use of a substoichiometric amount of reagent usually increases the selectivity of the separation process.

ISSN:0007-8980    

DOI:10.1080/10408347108542766

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The use of nuclear magnetic resonance for studying the structures, equilibria, and chemical dynamics of metal chelates is considerably more recent than its application to the study of organic compounds, and the early studies were performed by inorganic chemists rather than those whose interests lie in analytical chemistry. These studies were directed toward the geometrical isomers of metal chelates in the newly and rapidly expanding fields of inorganic chemistry. The initial studies of the aminopolycarboxylates opened up new applications of NMR, which provided a better understanding of the chemistry of metal chelates. The old question of the protonation scheme of these compounds was answered in a quantitative way with exceptional experimental simplicity. The fact that NMR provides a probe not only of molecular dimensions, but also into the behavior of individual metal-ligand bonds, provided a method of classification of the various types of metal-ligand bonding. It is important to observe that these studies were performed using aqueous solutions which is the home of metal-chelate chemistry for analytical applications. Earlier studies were in large part performed with aprotic solvents or solvents of low dielectric constant. The presence of the large solvent water peak was avoided by many researchers. However, much important information is available in the spectral features not blocked by the water peak.

ISSN:0007-8980    

DOI:10.1080/10408347108542767

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Enough experimental data on nonaqueous ion-exchange separations have been gathered to show that one is dealing with a field whose theoretical aspects are infinitely complicated. The separations can be based on several different types of chemical reactions. Apart from true ion exchange, sorption can take place by non-exchange reactions such as acid-base reactions or complex-formation, either by hydrogen bonding or by metal-ligand coordination. All these reactions can be influenced by a multitude of parameters such as solvent polarity, solvent-solute interaction by solvation or complex formation, solvent structure changes, solvent-resin matrix interaction, solvent-solvent interaction, acid-base properties of the solvent, non-exchange electrolyte invasion, and so on. Any one or several of these parameters may or may not be operative in a given case, and a given parameter can be of primary importance in one case and be only a minor contributing factor in another. In view of such complexity, one should not be surprised that the few attempts so far made to develop a theory of nonaqueous ion exchange were not too successful and could be applied only to a few rather simple cases. Even considering only one type of chemical reaction, the true ion exchange, the chances of ever arriving at a comprehensive theory appear to be pretty slim.

ISSN:0007-8980    

DOI:10.1080/10408347108542768

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor