Neocompact Sets and the Fixed Point Property

We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory.     

On-line coupling between chromatography and inductively coupled plasma mass spectrometry — a current assessment

The current state of on-line coupling between liquid chromatography and inductively coupled plasma mass spectrometry is reviewed. The applications can be divided into three subgroups by changing the importance of the coupling partners. An overview is given of applications in these subgroups, of its use as preconcentration and matrix elimination techniques, for the elimination of spectral interferences and as a tool for speciation analysis. A discussion of current and future development areas in on-line HPLC-ICP-MS is also included.     

Luminescent Labels—More than Just an Alternative to Radioisotopes?

Chemical, chromatographic, or spectrometric methods are generally unsuitable for the detection of molecules in the nano and subnanogram region because of their low sensitivity. The radioimmunoassay (RIA) developed by Yalow and Berson in 1959 combined the high sensitivity of radioactively labeled substances with the high specificity of immunological reactions for the first time. In this way it was possible to detect quantitatively the tiniest traces of substances in the presence of an excess of other, in some cases, similar foreign substances without prior enrichment. Immunoassays have certainly developed to become the most valuable analytical tool of in vitro diagnostics and are today routinely employed for the detection of endogenous and exogenous substances (e.g. hormones, tumor-associated proteins, bacteria, viruses, toxins, drugs, etc). The many disadvantages of radioactivity such as the required handling licenses, disposal costs, precautions necessary to prevent risks to health, short shelf-life, and limited sensitivity soon led to the search for other nonradioactive labeling methods. Encouraged by the development of light measuring techniques and the commercial availability of highly sensitive apparatus, radioactive isotopes as labels are today being replaced increasingly by enzymes, fluorophores, or luminophores. Some of the new luminescent labels have, however, not only facilitated replacement of radioisotopes, but also a breakthrough into what has until now been unattainable levels of sensitivity. The following article reviews the methods of luminescent labeling and their applications mainly in the area of immunoassays.