Analysis: biological specimens, problems

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. 

Reliable evaluation of the potential for human exposure to CDDs depends in part on the reliability of supporting analytical data from environmental samples and biological specimens. Historically, CDD analysis has been both complicated and expensive, and the analytical capabilities to conduct such analysis have been available through only a relatively few analytical laboratories. Limits of detection have improved greatly over the past decade with the use of high-resolution mass spectrometry, improvements in materials used in sample clean-up procedures, and with the use of known labeled and unlabeled chemical standards. Problems associated with chemical analysis procedures of CDDs in various media are discussed in greater detail in Chapter 6. In reviewing data on CDD levels monitored or estimated in the environment, it should be noted that the amount of the chemical identified analytically is not necessarily equivalent to the amount that is bioavailable (see Section 2.3) and that every measurement is accompanied with a certain analytical error. 

Finally, a note of caution is needed to secure proper handling of biological specimens for GC analysis. Many of the recommendations as well as the rules for GC analysis are similar to the requirements for other clinical determinations (collection rules, sample storage, transportation, etc.), but special needs for GC may sometimes arise. For example, while certain foreign compounds (preservatives, dietary artifacts, therapeutic drugs, etc.) may not matter in conventional determination, they may be a problem in GC analysis. A publication by Jellum [15] discusses this matter in some detail. 

Several investigators have used neutron activation analysis (NAA) to determine the aluminium content of biological specimens both with and without some chemical processing. Instrumental neutron activation analysis involves the bombardment of a sample with neutrons and the measurement of the radioactivity induced by nuclear reactions. No chemical processing is required. Upon activation Al (100% isotopic abundance) forms the radioactive AI nuclide by a (n,y) reaction. There are a number of attractive features in this technique which include excellent sensitivity with relative independence from matrix effects and interferences. Also, there is relative freedom from contamination since the sample is analyzed directly with minimal handling. One major problem is the need to... 

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. 

The soft biological tissue to be dealt with includes autopsy as well as biopsy specimens from various human body organs, e.g. liver, kidney, brain, lung, placenta and other connective tissues. No unified approach for handling of these tissues has been established despite the numerous problems during preparation of these samples for analysis. However, several reports are available on typical body tissues, e.g. kidney (Livingstone, 1971), liver (lyenger and Kasparek, 1977). 

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