Chemical analysis oxides

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is described in section Bl.25,2.1. The most connnonly employed x-rays are the Mg Ka (1253.6 eV) and the A1 Ka (1486.6 eV) lines, which are produced from a standard x-ray tube. Peaks are seen in XPS spectra that correspond to the bound core-level electrons in the material. The intensity of each peak is proportional to the abundance of the emitting atoms in the near-surface region, while the precise binding energy of each peak depends on the chemical oxidation state and local enviromnent of the emitting atoms. The Perkin-Elmer XPS handbook contains sample spectra of each element and bindmg energies for certain compounds [58]. 

One other very important attribute of photoemitted electrons is the dependence of their kinetic energy on chemical environment of the atom from which they originate. This feature of the photoemission process is called the chemical shift of and is the basis for chemical information about the sample. In fact, this feature of the xps experiment, first observed by Siegbahn in 1958 for a copper oxide ovedayer on a copper surface, led to his original nomenclature for this technique of electron spectroscopy for chemical analysis or esca. 

Analysis of Trace or Minor Components. Minor or trace components may have a significant impact on quaHty of fats and oils (94). Metals, for example, can cataly2e the oxidative degradation of unsaturated oils which results in off-flavors, odors, and polymeri2ation. A large number of techniques such as wet chemical analysis, atomic absorption, atomic emission, and polarography are available for analysis of metals. Heavy metals, iron, copper, nickel, and chromium are elements that have received the most attention. Phosphoms may also be detectable and is a measure of phosphoHpids and phosphoms-containing acids or salts. 

Elemental chemical analysis provides information regarding the formulation and coloring oxides of glazes and glasses. Energy-dispersive x-ray fluorescence spectrometry is very convenient. However, using this technique the analysis for elements of low atomic numbers is quite difficult, even when vacuum or helium paths are used. The electron-beam microprobe has proven to be an extremely useful tool for this purpose (106). Emission spectroscopy and activation analysis have also been appHed successfully in these studies (101). 

Chemical Analysis. Plasma oxidation and other reactions often are used to prepare samples for analysis by either wet or dry methods. Plasma excitation is commonly used with atomic emission or absorption spectroscopy for quaUtative and quantitative spectrochemical analysis (86—88). 

Chemical analysis showed that each organism contained up to 50% silica by weight. Each was coated with iron oxides, silt, and other deposits and corrosion products. In places, large deposit accumulations were clearly correlated with large numbers of organisms. 

These are semisolid or solid substances formed in nature from crude oils after the volatile components have evaporated and the remainder has undergone oxidation and polymerization. They are also referred to as bitumens, waxes, and pitch. These materials are believed to consist of mixtures of complex organic molecules of high molecular weight. As with crude oils, which contain thousands of different chemical compounds, an exact chemical analysis for identification and composition is impractical to perform on the solid deposits of petroleum. 

Chemical analysis of niobium oxide indicated that the purity of the final product depends strongly on the purity of the initial solution. Account should be taken of about 0.02-0.03% wt. cationic impurities, introduced due to interactions with metal parts of the equipment. The main added impurities are Fe, Ni, Cr, which originate mostly from the stainless steel filter. The purity of the final product can be significantly increased by using a filter made of niobium or other appropriate material. Nevertheless, the material obtained using a stainless steel filter is sufficient for use in ceramic applications or as an initial material for carbide manufacture. 

Ruthenium, (ethylenediaminetetraacetic acid)-chemical analysis, 1,488 Ruthenium, hexaammine-oxidation, 1,370 redox potential. 1,485... 

A second source of plutonium, dispersed more locally, is liquid effluent from fuel reprocessing facilities. One such is the fuel reprocessing plant at Windscale, Cumbria in the United Kingdom where liquid waste is released to the Irish Sea(6). Chemical analysis of this effluent shows that about one percent or less of the plutonium is in an oxidized form before it contacts the marine water(7). Approximately 95 percent of the plutonium rapidly adsorbs to particulate matter after discharge and deposits on the seabed while 5 percent is removed from the area as a soluble component ). Because this source provided concentrations that were readily detected, pioneering field research into plutonium oxidation states in the marine environment was conducted at this location. 

While these calculations provide information about the ultimate equilibrium conditions, redox reactions are often slow on human time scales, and sometimes even on geological time scales. Furthermore, the reactions in natural systems are complex and may be catalyzed or inhibited by the solids or trace constituents present. There is a dearth of information on the kinetics of redox reactions in such systems, but it is clear that many chemical species commonly found in environmental samples would not be present if equilibrium were attained. Furthermore, the conditions at equilibrium depend on the concentration of other species in the system, many of which are difficult or impossible to determine analytically. Morgan and Stone (1985) reviewed the kinetics of many environmentally important reactions and pointed out that determination of whether an equilibrium model is appropriate in a given situation depends on the relative time constants of the chemical reactions of interest and the physical processes governing the movement of material through the system. This point is discussed in some detail in Section 15.3.8. In the absence of detailed information with which to evaluate these time constants, chemical analysis for metals in each of their oxidation states, rather than equilibrium calculations, must be conducted to evaluate the current state of a system and the biological or geochemical importance of the metals it contains. 

A second unusual EPR spectrum was observed in the oxidized (as-isolated) protein (Fig. 3). This spectrum, which was assigned to an S = z system, was not reminiscent of any Fe-S cluster. Indeed, with g-values of 1.968, 1.953, and 1.903, it looked more like a molybdenum or tungsten spectrum. However, chemical analysis ruled out the possibility that this EPR spectrum arose from Mo or W, and the spectrum was assigned to an Fe-S center instead. The spin concentration, however, was sub stoichiometric and sample-dependent. Furthermore, when the as-isolated protein was oxidized with ferricyanide, it became EPR silent. This, together with the iron determination and the fingerprint of the reduced protein, led Hagen and colleagues to the... 

This chapter will explain the setup and methodology used for the field retrieval study. The physical and chemical analysis techniques used to study the oxidation of the tire rubber, along with the data analysis developed to interpret the results, will also be explained. Then, the development of an oven-aging protocol that attempts to reproduce the mechanism and rate of tire field aging will be described. 

Induced dissolution is also a well known phenomenon and frequently applied in chemical analysis. To dissolve platinum easily it was suggested by Ropp that the sample should be alloyed with silver or copper, the alloys being easily soluble even in dilute acids. Anhydrous chromic chloride, insoluble in water and dilute acids, becomes easily soluble by adding metallic magnesium or zinc to the dilute acid . In this case the chromium(III) compound is reduced to chro-mium(II), which will be oxidized by the solvent to water-soluble chromium(III)... 

Another peculiarity of the study is that the use of a biological system has allowed the authors to hypothesize a possible mechanism of action of the leachate as a mixture, hypothesis that could have been drafted on the basis of the only knowledge derived by chemical analysis. Researchers suggest that leachate inhibits cell proliferation at low doses probably inducing a reversible cell cycle arrest that becomes irreversible at high doses, probably due to leachate-induced oxidative stress. This activity is mainly due to the chemical compounds extracted in the aqueous phase. Similar effects were noticed by previous investigations on other human cells (human peripheral blood lymphocytes and a human breast cancer cell line, MCF-7) [31, 32], supporting the hypothesis that cells that survive the initial insult from leachate constituents maintains the potential to proliferate until the effects on cell metabolism lead to death. 

Direct measurement of the absolute binding energy and widths of core (X-ray) and valence (UV) bands. The core levels do not participate in bonding, hence each element gives a characteristic XPS spectrum electron spectroscopy for chemical analysis (ESCA). ESCA gives the elemental composition of the surface of a solid sample (except H), the relative amounts of each element present, its oxidation state and some information on the chemical environment around each element. In addition, it is capable of providing an estimate of the depth of a deposited overlaycr... 

With respect to the UHV-based techniques capable of providing chemical analysis, such as ESCA, AUGER, etc., several such studies have been performed. However, these studies were, by and large, performed on very thick oxide layers, formed after anodic oxidation of the Pt for many hours. Results from these studies thus have little bearing on the nature of the oxides formed on potential cycling. Part of the reason why these studies used such thick films lies in the considerable difficulty of detecting the thin oxide films formed during a potential sweep, even with relatively sensitive techniques. 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

Evidences about the successful intercalation of the Rh-TPPTS complex (qualitative and quantitative) between the layers of both LDHs were also provided by the XPS and DRIFTS results. XPS composition was in a very good concordance with chemical analysis. As shown in Table 2, the binding energies of the constitutive elements in both LDHs are typical for their oxidation states, while for Rh it corresponds to (I) state [13] that is again in accordance with the oxidation state of the expected complex. 

Cr-ZSM-5 catalysts prepared by solid-state reaction from different chromium precursors (acetate, chloride, nitrate, sulphate and ammonium dichromate) were studied in the selective ammoxidation of ethylene to acetonitrile. Cr-ZSM-5 catalysts were characterized by chemical analysis, X-ray powder diffraction, FTIR (1500-400 cm 1), N2 physisorption (BET), 27A1 MAS NMR, UV-Visible spectroscopy, NH3-TPD and H2-TPR. For all samples, UV-Visible spectroscopy and H2-TPR results confirmed that both Cr(VI) ions and Cr(III) oxide coexist. TPD of ammonia showed that from the chromium incorporation, it results strong Lewis acid sites formation at the detriment of the initial Bronsted acid sites. The catalyst issued from chromium chloride showed higher activity and selectivity toward acetonitrile. This activity can be assigned to the nature of chromium species formed using this precursor. In general, C r6+ species seem to play a key role in the ammoxidation reaction but Cr203 oxide enhances the deep oxidation. 

As shown in the previous sections, identifying a small amount of a protein (in the order of tens of picomoles) represents a difficult problem for traditional methods of chemical analysis. The situation is even more complicated when a protein mixture of variable composition should be identified in a complex matrix containing dyes, oils, inorganic pigments, lime, etc. moreover, the analysed materials come often from the Middle Ages or even ancient times and the proteins in them could have undergone various modifications (e.g. oxidation, photodecomposition and microbial digestion) over the centuries. 

---