Structural materials, trace-element concentrations

TABLE 6.4 Trace-Element Concentrations in Structural Materials... 

Wool belongs to the family of proteins called a-keratins, which also inclnde materials such as hooves, horns, claws, and beaks (31). A characteristic feature of these hard keratins is a higher concentration of snlfnr than soft keratins, such as those in skin. Although clean wool consists mainly of proteins, wool also contains approximately 1% by mass of nonproteinaceons material. This consists mainly of lipids plus very small amounts of polysaccharide material, trace elements, and, in colored fibers, pigments called melanin. The lipids are both structural and free. 

Like most trace elements, nickel can activate various enzymes in vitro, but no enzyme has been shown to require nickel, specifically, to be activated. Howevei, mease has been shown to be a nickel metalloenzyme and has been found to contain 6 to 8 atoms of nickel per mole of enzyme (Fishbein et al.. 1976). RNA (ribonucleic add) preparations from diverse sources consistently contain nickel in concentrations many times higher than those found in native materials from which the RNA ts isolated (Wacker-Vallee, 1959 Sunderman, 1965). Nickel may serve to stabilize the ordered structure of RNA. Nickel may have a role in maintaining ribosomal structure (Tal, 1968, 1969). These studies and other information have led to the suggestion that nickel may play a role in nucleic acid and/or protein metabolism. 

A wide variety of solvents, reagents, and structural materials encountered normally in the trace-element analysis of seawater have been analyzed for trace-element impurities by neutron activation analysis and gamma (y)-ray spectrometry.17 Some of the results obtained for 10 trace elements are shown in Table 6.4 and indicate that many substances contain high impurity levels of various elements. Particular note should be made of the high concentrations of zinc in... 

At x 0.429( the Region B particles corresponding to the cubic phase dominate the structures as seen by S.E.M. As before, for both composite and coprecipitated samples, this phase appears (by EDX) to consist primarily of Y, B1 and Ba, with traces of Ca and Cu. The remainder of the copper Is mostly present as small, smooth chunks, which. In the composite material, contain only traces of the other elements, and In the coprecipitated sample, contain large concentrations of both strontium and calcium. It seems likely that both phases In these complex systems exist as solid solutions, and that the exact partition of the elements between the phases Is a klnetlcally controlled phenomenon, determined by the starting materials from which they were synthesized. 

The materials of interest for earth sciences are generally very complex from the chemical viewpoint, and may sometimes contain most of the elements of the periodic table, with concentrations varying from the trace- to the major-element level and with variable spatial distribution (zoning). As a consequence, their complete structural and chemical characterization is possible only by means of in situ analytical methods that are able to solve specific measurement problems. The starting material is often available in very small amounts (e.g., some crystals) thus, the requirement of minimum (or even null) sample consumption is also important. 

Microanalysis, the detection and identification of materials present in small size but relatively high concentration, is distinct from trace analysis, which is concerned with the characterization of small concentrations of material. Organic microanalysis is usually taken to mean elemental analysis (primarily C, H, O, N, P, S, Cl, Br, 1, and Si), and functional group analysis (acetyl, carboxyl, benzoyl, amino, nitro, hydroxy, etc.) on samples usually 1-10 mg in size. The semiquantitative results, accurate to about 10%, serve as a measure of impurities, or inhomogeneity, or for structure determination in solid organic substances. Accurate results of 1 % or better may be expected when large (1 g) samples are taken for analysis and the entire chemical apparatus is scaled upward in size. However, small samples take less time to analyze, so the micro methods are more popular than macro methods. 

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