Composition, analysis variety

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

A variety of infrared methods have been available for the simple problems of verifying the purity of the initial resin components and mixtures of those components. The simplest possible test of the purity of a reactant is to compare its spectrum with a known standard. Subtractive methods may be employed to emphasize the most significant intensity changes 19). Composition analysis of the blended resins and hardeners becomes more difficult. In some cases, one may simply select characteristic isolated absorption bands for each component and estimate the composition by comparison to standard spectra of known composition 20,21). 

It was shown from the study of styrene and MMA in a KNOa-DMF system using tracer techniques for the composition analysis that the free-radical contribution is apparently confined to the first few percent of polymerization, whereas at later stages the reaction is anionic (34). This is consistent with the inhibitor studies. On the same monomer pair with a variety of solvents with ammonium salts, only with tetrahydrofuran did a possible free-radical reaction accompany the anionic propagation, with the others, DMF and dimethylacetamide, as well as without solvent, an anionic reaction accompanying the free radical one was assumed (35). 

In the beginning, NIR was used for compositional analysis of only grains, beans and seeds which are relatively low moisture products. NIR is now being used for compositional analysis of variety of products including fruits and vegetables which are high moisture products. As the software and hardware of NIR improved, the scope of NIR application has been expanding to diversified fields such as textile, oil, pharmacy, and medical science. 

In response to the oil spill identification need and specific site investigation needs, attention has focused on the development of flexible, tiered analytical approaches, which facilitate the detailed compositional analysis by GC-MS, GC-FID, and other analytical techniques that quantitatively determine a broad range of individual petroleum hydrocarbons. A variety of diagnostic ratios, especially ratios of PAH and biomarker compounds, for interpreting chemical data from oil spills have been proposed. 

A number of studies have focused on the molecular structure of coal [29-31]. The structures can be derived using data from a variety of sources, including coal atomic composition, analysis of pyrolysis products, extraction or liquefaction treatments of coal samples, and spectroscopic analyses using GC/MS, NMR, and IR. In our study, the method of Py-GC-MS, which consists of a CDS 5250 pyrolysis autosampler and focus GC-DSQII, has been used to study the pyrolysis of coal in order to obtain information about coal stmcture. 

Analysis of plastics is a complex task and involves preliminary tests, determination of nonmetallic and metallic elements, analysis of functional groups and double bonds, molecular weight determinations, chemical compositional analysis, sequence length distribution in copolymers, determination of tacti-city and branching in polymers, and analysis of additives. Because of the great variety in structures in commercially produced plastics, the number of methods that can be applied for their analysis is considerable. 

Pyrolysis gas chromatography has been used extensively to determine compositional analysis of polymeric materials. It is a technique that has long been used in a variety of investigative fields because it produces volatile compounds from macromolecules that are neither volatile nor soluble. Examples are polymers, rubbers, paint films, and resins. Volatile fragments are formed and introduced into the chromatographic column for analysis. A polymer can be used as an example to illustrate the use of this technique, which consists of two steps. The injection port is heated to about 250C ... 

Montealegre, RR Peces, RR Vozmediano, JLC Gascuen, JM Romero, EG. Phenohc compounds in skins and seeds of ten grape Vitis vinifera varieties grown in a warm climate. Journal of Food Composition Analysis 2006, 19,687-693. 

Fig.1 An integrated and iterative approach to the hazard assessment and characterisation of new GM varieties. Compositional Analysis (the subject of this chapter) is an essential component but represents only one part of the overall scheme. (Reprinted fromKonig et al., 2004. 2004. With permission from Elsevier)...

Iron oxides and hydroxides are the most important iron-bearing constituents of soils, sediments and clays. To characterize the samples, i.e. the identification of the different minerals present and the determination of their morphology and chemical composition, a variety of standard techniques are commonly used such as X-ray and electron diffraction, chemical analyses, optical and electron microscopy, infrared spectroscopy and thermal analysis (DTA, DTC,...). Most of these techniques are further applied in conjunction with selective dissolution or other separation methods in order to obtain more specific information about particular components in the complex soil system. In addition to all those characterization methods, MS has proven to be a valuable complementary technique for the study of these kinds of materials and in particular for the characterization of iron oxides and hydroxides which are usually poorly crystallized. 

Compositional analysis is concerned with determining structural relationships in the molecules present in a sample. Inhared spectroscopy is the most commonly used tool for qualitative chemical analysis of viscous oils. Descriptions and tables of characteristic absorbance for a variety of organic functional groups are readily available in many textbooks. Techniques for quantitative anal3rsis for many additives and some hydrocarbon types are available, although few have been issued as ASTM standards. Reports on new methods are commonly reported in the chemistry literature. To locate information on new analytical methods, a most useful reference is the bi-aimual Application Review published by the American Chemical Society. These have appeared recently in the June 15 issue of Analytical Chemistry in odd-numbered years. Recent reviews cover coal, crude oil, shale oil, heavy oils (natural and refined), lubricants, natural gas, and refined products and source rocks. Extensive references to original research papers are provided. A complimentary Fundamental Review covering the basic analytical techniques is published in even-numbered years. 

Analysis of Surface Molecular Composition. Information about the molecular composition of the surface or interface may also be of interest. A variety of methods for elucidating the nature of the molecules that exist on a surface or within an interface exist. Techniques based on vibrational spectroscopy of molecules are the most common and include the electron-based method of high resolution electron energy loss spectroscopy (hreels), and the optical methods of ftir and Raman spectroscopy. These tools are tremendously powerful methods of analysis because not only does a molecule possess vibrational modes which are signatures of that molecule, but the energies of molecular vibrations are extremely sensitive to the chemical environment in which a molecule is found. Thus, these methods direcdy provide information about the chemistry of the surface or interface through the vibrations of molecules contained on the surface or within the interface. 

Chemical Composition. Chemical compositional data iaclude proximate and ultimate analyses, measures of aromaticity and reactivity, elemental composition of ash, and trace metal compositions of fuel and ash. All of these characteristics impact the combustion processes associated with wastes as fuels. Table 4 presents an analysis of a variety of wood-waste fuels these energy sources have modest energy contents. 

Composition. Molasses composition depends on several factors, eg, locality, variety, sod, climate, and processing. Cane molasses is generally at pH 5.5—6.5 and contains 30—40 wt % sucrose and 15—20 wt % reducing sugars. Beet molasses is ca 7.5—8.6 pH, and contains ca 50—60 wt % sucrose, a trace of reducing sugars, and 0.5—2.0 wt % raffinose. Cane molasses contains less ash, less nitrogenous material, but considerably more vitamins than beet molasses. Composition of selected molasses products is Hsted in Table 7. Procedures for molasses analysis are avadable (59). 

In given work the possibilities enumerated above of varieties of thermal analysis used to reseai ch of solid solutions of hydrated diphosphates with diverse composition. So, for example, the results of differential-thermal analysis Zn Co j P O -SH O showed, that it steady in the time of heating on air to 333 K. A further rise of temperature in interval 333 - 725 K is accompanied with the masses loss, which takes place in two basic stages, registered on crooked TG by two clear degrees, attendant to removal 4,0 and 1,0 mole H O. On crooked DTA these stages dehydration registers by two endothermic effects. In interval 603 - 725 K on crooked DTA is observed an exothermal effect. 

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