Analysis: biological specimens, problems methods

Electron probe and X-ray fluorescence methods of analysis are used for rather different but complementary purposes. The ability to provide an elemental spot analysis is the important characteristic of electron probe methods, which thus find use in analytical problems where the composition of the specimen changes over short distances. The examination of the distribution of heavy metals within the cellular structure of biological specimens, the distribution of metal crystallites on the surface of heterogeneous catalysts, or the differences in composition in the region of surface irregularities and faults in alloys, are all important examples of this application. Figure 8.45 illustrates the analysis of parts of a biological cell just 1 pm apart. Combination of electron probe analysis with electron microscopy enables visual examination to be used to identify the areas of interest prior to the analytical measurement. 

His laboratory is concerned with the analysis of a wide range of materials which include a variety of biological specimens, mineral samples, air particulate matter, and water samples. The information obtained is used to evaluate various individual and environmental problems. Two of the techniques which have been used for water analysis are atomic absorption (J, 4) and flame emission (2) spectroscopy, and a study of factors aflFecting these methods is described here. The samples came from a number of sources which included well water and city water. Consequently, the concentration ranges of some of the elements were quite wide. Five determinations were made daily on both the samples and standards for each element over a period of several months to provide suflBcient data for an adequate evaluation of precision. At present, ten elements (Na, K, Ca, Mg, Zn, Pb, Mn, Cu, Fe, and Ni) are being determined quantitatively. 

Only trace amounts of copper are present in biological material, in the general range 0.1-10 /ig/g (0.1-10 ppm). These trace amounts are in complex mixture with innumerable other metals and elements, some of which are present in much larger quantities. In addition the sample size is often limited, as in blood samples from infants and small animals or needle biopsy specimens from tissues. Methods for copper therefore must be highly sensitive as well as highly specific, since the analyst faces the problem of trace analysis on a micro- or ultramicroscale. 

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