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Purification and fractionation

Jeffries-EI, E. E. Sheina, J. R. Cooper and R. D. McCullough. Regioregular poly(3-alkylthiophene) conducting block copolymers. Polymer 46(19), 8582-8586 (2005), Copyright 2005, with permission from Elsevier [Pg.172]

A systematic study by Trznadl el al. of bulk properties vs M summarized the electronic changes [90]. Thin-film cyclic voltammetry (CV) showed an oxidation at 0.74 V in ali samples that decreased in intensity with increasing Mn. Additional oxidations at 0.58-0.60 and 0.97-1.00 V, absent from ir-PHT and the [Pg.172]


Many problems need to be solved before chemurgic materials can be economically used as feedstocks. Among these problems are the recovery, purification, and fractionation of the diverse materials. However, none of these problems are insurmountable. Serious concerns are the supply of the raw material, the relative costs of competitive materials, and competition with other uses for the raw materials. Competition is particularly significant because materials, such as wood, could easily be used in many cases for pulping or even higher value products, such as stmctural timber. Municipal soHd waste offers a substitute raw material with few other uses (33). [Pg.450]

Preparation. For the carbo-thermal production of silicon and ferro-silicon, arc furnaces are used. Another method starts with SiF4. After purification and fractional distillation SiF4 can be reduced to silicon with Na. Alternatively the following reaction can be used ... [Pg.498]

Analytical methods for determining disulfoton in environmental samples are reported in Table 6-2. The steps included in the methods are solvent extraction, purification and fractionation, and gas chromatographic analysis. Other analytical techniques, including capillary gas chromatography with mass selective detection (Stan 1989), high-performance liquid chromatography with either mass spectrometric (MS) or MS-MS detection (Betowski and Jones 1988), have been used to determine disulfoton in environmental samples. [Pg.160]

Most existing methods are based on instrumental analysis involving exhaustive sample pretreatment and preconcentration steps, followed by purification and fractionation before final chromatographic separation and detection. For fat and oil samples, dissolving the lipids in an appropriate solvent is usually the first treatment. This has been achieved by melting the fat at 90°C followed by LLE or direct solid liquid extraction (SEE) with an apolar solvent [37], column extraction with a mixture of apolar solvents after drying of the sample with anhydrous Na2S04, Soxhlet extraction and/or sonication with apolar solvents. Typically, sample intake is between 0.5 g and 1 g and quantitative recoveries >60% have been reported. [Pg.21]

C.Y. Ryu, J. Han, W. Kim, Large scale purification and fractionation of block copolymers using silica gels. Proceedings of the lUPAC Congress on CD, Turin, Italy, 2007. [Pg.503]

Purification and Fractionation of 90% BenzoL—Commercial benzene is far from pure and contains homologues (chiefly toluene) and thiophen as well as basic substances. On removal of the bases with dilute acid and the thiophen with cone, sulphuric acid, fairly pure benzene may be obtained by fractional distillation of the residue. 90% benzol contains about 80—82% benzene, 14—15% toluene, and about 3% xylenes. The term means that 90% by volume of the benzol can be distilled off up to 100°. [Pg.24]

Crosslinked dextran gels (for example, Sephadex ) have been used extensively for the purification and fractionation of various biological substances, including the recovery of proteins from liquid wastes and effluent streams.343"-347... [Pg.305]

In environmental chemical analytical procedures such as extraction, purification, and fractionation with basic aluminum oxide and activated carbon,... [Pg.290]

In chemical analytics PCDTs and PCTAs behave very similar to PCDDs and PCDFs. The chromatographic behavior of PCDTs is similar to that of PCDDs. Purification and fractionation with aluminum oxide and activated carbon originally developed for the analysis of PCDDs and PCDFs can be used [28,44]. [Pg.300]

Fractionation, on the other hand, is the subdividing of humic substances according to some property related to their molecular composition. Because humic substances are ill defined there will inevitably be some confusion between these processes of purification and fractionation, especially since the same or very similar techniques are used in both cases. Nevertheless, the distinction between the two should be clearly made and understood and adhered to by research workers in this field. [Pg.388]

Since its introduction some years ago gel permeation chromatography has become a powerful tool in the study of naturally occurring polymers. While primarily devised and used for studying proteins, the technique has been applied to a wide variety of materials and has been used in the study of humic substances since the early 1960s. Gel permeation chromatography is a rapid, cheap, and very versatile technique. It can be used as a method for separation, purification, and fractionation as well as for determinations of molecular weights and molecular weight distributions of polymer systems. A review of the principles and applications of the technique is provided by Fisher (1969). [Pg.395]

The synthesis of polypeptide hybrid block copolymers is an area that has been under study for three decades. Initially, this field suffered from limitations in the synthesis of the polypeptide components that required excessive sample purification and fractionation to obtain well-defined copolymers. In recent years, vast improvements in NCA polymerizations now allow the synthesis of hybrid block copolymers of controlled dimensions (molecular weight, sequence, composition, and molecular weight distribution). Such well-defined materials will greatly assist in the identification of new self-assembled structures possible using ordered polypeptide segments, as well as yield new materials with a wide range of tunable properties. [Pg.17]

Selection of Methods. The purification and analysis of a chemically modified protein can be as formidable a task as the chemical modification itself (10). An important general rule to follow in the selection of the proper procedures for the purification and fractionation of modified proteins is that the selections must be on an operational basis. Any method of purification should be selected with regard to the type of chemical modification, the manner in which modification is done, and the purpose of the modification. It is frequently necessary to change the original chemical modification to give a product which can be purified more easily. Similar reasonings may also be applied to the selection of techniques for analyses of the products. [Pg.27]

Methods to obtain natural organics from surface waters, their purification and fractionation witl be reviewed. Many of the techniques described were used in this study. Subsequently, this led to the selection of a suitable process for NOM concentration for this study (see Appendix 1). [Pg.5]

Figure 9. Purification and fractionation of Azotobacter N>ase specific activity is nmoles reduced/min mg... Figure 9. Purification and fractionation of Azotobacter N>ase specific activity is nmoles reduced/min mg...
White, D. H., Jr., Conpressed Air and Gas Purification and Fractionation for High Purity Applications by Improved PSA Processes, Separ. Sci. Technol, 43, 2298-2306 (July 2008). [Pg.878]

Hydroxyapatite has been found to be particularly useful in the chromatographic purification and fractionation of DNA. Double-stranded DNA binds more strongly than single-stranded varieties and hydroxyapatite can be used for their separation [17]. [Pg.1342]

At the present time, TLC is an indispensable tool for synthetic carbohydrate chemistry. This method together with gas-liquid chromatography permits the analysis of compounds which cannot be detected on paper chromatograms. GLC, however, is restricted to compounds which can be volatilized without degradation, whereas TLC affords a rapid analysis under mild conditions. Column chromatography employing silica gel or alumina is a standard method for purification and fractionation of hydrophobic derivatives of carbohydrates, but thin-layers afford a sharper resolution of similar compounds. [Pg.830]

Recently, there has been an increasing interest in the use of supercritical fluid extraction (SEE) with carbon dioxide (CO2) as a solvent. This process uses the properties of gases above their critical points to extract selective soluble components from a raw material. Carbon dioxide is an ideal solvent for the extraction of natural products because it is nontoxic, nonexplosive, readily available, and easy to remove from extracted products [3,6]. SFE has the abihty to use low temperatures, leading to less deterioration of the thermally labile components in the extract. In addition, SFE is typically carried out in the absence of air which also ensures minimal alteration of the active ingredients and preservation of the curative properties [46, 47]. SC CO2 is generally efficient in the purification and fractionation of hydrophobic compounds, such as flavonoids and cinnamic acid derivatives from plant matrixes [49]. [Pg.2070]


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