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In materials science, solid state physics, and many other fields of modern technology there is rapidly increasing interest in obtaining accurate analytical data. In addition to the determination of the concentration of traces of an element in the bulk material, information on its distribution within the sample or on the surface of the sample is required. The analytical chemist is always faced with new problems showing the limitations of his methods. In extreme trace analysis the systematic errors inherent in the methods frequently cause the analytical results to be incorrect by several orders of magnitude.  The first part of this contribution deals with the sources and the identification of such errors.  In the second part examples from the author's laboratory of how to obtain accurate results in extreme trace metal analysis will be presented.  In all the methods discussed, optimized decomposition and separation steps - checked by means of radioactive tracers if possible - are combined with a suitable technique for determination of the isolated trace element.  The samples are preferably decomposed in a special pressure bomb, with highly purified acids. The trace elements are then separated from the matrix by conversion into gaseous products or by electrolytical deposition in a hydrodynamic system.  The final determination is accomplished by using very sensitive spectrometric methods, e.g. furnace atomic absorption spectrometry (FAAS), optical emission spectrometry (OES) with microwave induced plasma (MIP) and hollow-cathode excitation.  Dust-free laboratories, chemically inert materials for construction of the necessary apparatus, highly purified reagents, and special microtechniques are very important factors in reducing systematic errors. Furthermore, new developments in the field of extreme trace analysis will only be successful if at least two independent methods are available to solve a certain analytical problem and thus provide a crosscheck of the accuracy of the results.  It must be pointed out that only by the application of such expanded multi-step procedures to a variety of different matrices is it possible to be sure of the composition of standard reference materials for instrumental multi-element methods (e.g. mass spectrometry and instrumental activation analysis).

Problems, limitations, and future trends in the analytical characterization of high-purity materials