A trace elements

Gallium is often found as a trace element in diaspore, sphalerite, germanite, bauxite, and coal. Some flue dusts from burning coal have been shown to contain as much 1.5 percent gallium. 

For the purposes of this illustration, suppose that the level of of a trace element (X) is to be determined in a sample and that the element has two suitable isotopes (A,B). 

Economic Aspects. Table 3 shows that mbber production is the largest market for zinc oxide the downturn in 1980 resulted from a drop in tire production because of the production trend to smaller tires, more importation of tires, and a recession. The drop in paint usage reflects the trend to water-base paints, which originally contained no zinc oxide. However, its growing use in such paints is based upon improved formulations based on zinc oxide. The increased use in agriculture is a result of the realization of the importance of zinc as a trace element. The rise in use of zinc-oxide-coated paper for photocopying is followed by a slackening in use because of a shift to plain-paper copiers. 

Whereas certain rocks of igneous origin formed by melting and recrystallization can include minerals enriched in the lanthanides (4), cerium is usually present as a trace element rather than as an essential component. Only a few minerals in which cerium is an essential stmcture-defining component occur in economically significant deposits. Two minerals supply the world s cerium, bastnasite [68909-13-7] LnFCO., and monazite [1306-41 -8] (Ln,Th)PO. ... 

The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

Yes, semiquantitative without standards quantitative with standards. Not a trace element method. 

Figure 4 Calculated minimum concentration of a trace element in thin and thick carbon...

Although SSMS cannot be considered a surface technique due to the 1-5 rm penetration of the spark in most materials, few other techniques can provide a trace elemental survey analysis of surfaces consisting of films or having depths of interest... 

D SIMS measurements (Fig. 3.29) show that this layer is still present in the compacted material. Carbonitrides are precipitated in small particles with a diameter of 30 nm inside the particles. The distribution of Ca" ions is shown as an example of a trace element with a concentration in the ppm range. 

Andreae, M. O. (1979). Arsenic speciation in seawater and interstitial waters the role of biological-chemical interactions on the chemistry of a trace element. Limnol. Oceanog. 24,440-452. 

Although Fe is required as a trace element, its uptake is critically regulated since excess leads to the generation of toxic hydroxyl radicals, and complex interactions involving Fe(II) and Fe(HI) exist within the cell (Touati et al. 1995). The role of Fe(III)-complexing siderophores in maintaining homeostasis has been noted in Chapter 3, Part 5. Details of the role of Fe and its relation to the... 

Ecologically, copper is a trace element essential to many plants and animals. However, high levels of copper in soil can be directly toxic to certain soil microorganisms and can disrupt important microbial processes in soil, such as nitrogen and phosphorus cycling. Copper is typically found in the environment as a solid metal in soils and soil sediment in surface water. There is no evidence that biotransformation processes have a significant bearing on the fate and transport of copper in water. 

Evolution did not use this element, only in certain plants is it important as a trace element. The element became well-known because of heat-resistant borosilicate glasses. Boranes are chemically interesting as B-H bonds react very specifically. Perborates are used in laundry detergents (Persil). The hardness of cubic boron nitride approaches that of diamond. Amorphous (brown) boron burns very quickly and gives off much heat and is therefore used in solid-propellant rockets and in igniters in airbags. 

The reddish metal was already known in prehistoric times. It occasionally occurs as a native metal, but mostly in conspicuous green ores, from which it is extracted relatively easily. It is convenient to work, but not very hard. Not very optimal as a tool ("Otzi the Iceman" had a copper axe with him). Only through the addition of tin is the more useful bronze obtained. Its zinc alloy is the versatile and widely used brass. Copper is one of the coinage metals. Water pipes are commonly made of copper. Its very good thermal and electrical conductivity is commonly exploited (cable ), as well as its durability (roofs, gutters), as the verdigris (basic copper carbonate) protects the metal. Cu phthalocyanines are the most beautiful blue pigments. Seems to be essential to all life as a trace element. In some molluscs, Cu replaces Fe in the heme complex. A 70-kg human contains 72 mg. 

Although it is toxic in large doses, selenium is an essential micronutrient in all known forms of life. It is a component of the unusual amino acids selenocys-teine and selenomethionine. In humans, selenium is a trace element nutrient. 

In recent years, the physiological role of selenium as a trace element has created considerable speculation and some controversy. Selenium has been reported as having carcinogenic as well as toxic properties other authorities have presented... 

For example, X-ray fluorescence spectrometry may provide rapid but rather imprecise quantitative results in a trace element problem. Atomic absorption spectrophotometry, on the other hand, will supply more precise data, but at the expense of more time-consuming chemical manipulations. 

Figure 1. Conceptual model of the important physicochemical processes, leading to the uptake of a trace element by an aquatic microorganism...

The evolution of a concentration profile depends on how the velocity changes with concentration. It is left to the reader to show by taking the derivative of equation (8.3.17) at constant

trace element i, the last expression is the derivative of its... 

A related problem is the evolution of a trace-element ratio with crystallization... 

The residence time of a trace element is xJaLi. compatible elements can be thought of as reactive and have shorter residence times than inert incompatible elements. As shown in Chapter 7, equation (9.4.4) can be integrated from 0 to t into equation (7.2.12)... 

This may be the reason why silicon is essential, namely that it keeps aluminium in a non-toxic form as aluminium silicate. While silicon is required as a trace element in most animals, in plants, particularly grasses, and in many unicellular organisms, such as diatoms4, it is a major structural element. The importance of phosphorus and sulfur is obvious, the latter often associated with iron in an important family of proteins that contains iron-sulfur clusters. 

Sol id Sol utions. The aqueous concentrations of trace elements in natural waters are frequently much lower than would be expected on the basis of equilibrium solubility calculations or of supply to the water from various sources. It is often assumed that adsorption of the element on mineral surfaces is the cause for the depleted aqueous concentration of the trace element (97). However, Sposito (Chapter 11) shows that the methods commonly used to distinguish between solubility or adsorption controls are conceptually flawed. One of the important problems illustrated in Chapter 11 is the evaluation of the state of saturation of natural waters with respect to solid phases. Generally, the conclusion that a trace element is undersaturated is based on a comparison of ion activity products with known pure solid phases that contain the trace element. If a solid phase is pure, then its activity is equal to one by thermodynamic convention. However, when a trace cation is coprecipitated with another cation, the activity of the solid phase end member containing the trace cation in the coprecipitate wil 1 be less than one. If the aqueous phase is at equil ibrium with the coprecipitate, then the ion activity product wi 1 1 be 1 ess than the sol ubi 1 ity constant of the pure sol id phase containing the trace element. This condition could then lead to the conclusion that a natural water was undersaturated with respect to the pure solid phase and that the aqueous concentration of the trace cation was controlled by adsorption on mineral surfaces. While this might be true, Sposito points out that the ion activity product comparison with the solubility product does not provide any conclusive evidence as to whether an adsorption or coprecipitation process controls the aqueous concentration. 

Occurrence. Indium is widely spread in nature, generally in very low concentrations (0.1 ppm, earth s crust). Indium is present as a trace element in many minerals, such as sphalerite. 

The need to include a variety of minerals in experimental diets has already been mentioned this was especially stressed (1920-1930) by Boyd-Orr, the director of the Rowett Institute for Animal Nutrition in Scotland. Increasingly refined food sources led to the identification of large numbers of trace elements (e.g., Cu, Mn, Mo, Zn) whose importance in the diet was suggested from hydroponic experiments with plant seedlings. Cobalt is an example of such a trace element. Vitamin Bj2 is synthesized by bacteria in the rumens of sheep and cattle but is absent from their fodder. In Australia, sheep feeding on cobalt-deficient pastures failed to thrive because vitamin B12 could no longer be made. 

Schwartz, K., Milne, D.B. and Vinyard, E. (1970). Growth elfects of tin compounds in rats maintained in a trace element-controlled environment, Biochem. Biophys. Res. Comm., 40, 22-29. 

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