Chemical precipitation separation method procedure

However, for the past 30 years fractional separation has been the basis for most asphalt composition analysis (Fig. 10). The separation methods that have been used divide asphalt into operationally defined fractions. Four types of asphalt separation procedures are now in use ( /) chemical precipitation in which / -pentane separation of asphaltenes is foUowed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D2006) (2) solvent fractionation separation of an "asphaltene" fraction by the use of 1-butanol foUowed by dissolution of the 1-butanol solubles in... 

In view of the selective character of many colorimetric reactions, it is important to control the operational procedure so that the colour is specific for the component being determined. This may be achieved by isolating the substance by the ordinary methods of inorganic analysis double precipitation is frequently necessary to avoid errors due to occlusion and co-precipitation. Such methods of chemical separation may be tedious and lengthy and if minute quantities are under consideration, appreciable loss may occur owing to solubility, supersaturation, and peptisation effects. Use may be made of any of the following processes in order to render colour reactions specific and/or to separate the individual substances. 

Wahl and Deck were able to obtain an estimate of an assumed second-order rate coefficient ( 10 l.mole" .sec at 4°C) using a separation procedure based on the extraction of Fe(CN)e by a chloroform solution of Ph AsCl, in the presence of the ions Co(CN)g and Ru(CN)6, to reduce the exchange between the iron species in the two liquid phases. A similar estimate was obtained using a precipitation method in the presence of the carrier Ru(CN)6. A direct injection technique was used as short reaction times were necessary. Wahl has reviewed the large induced exchanges occurring in the chemical separation methods. The extraction procedure when the carriers Co(CN)6 and Ru(CN) are present provides the most satisfactory method of separation. ... 

Radiotracers are uniquely well suited to such studies. The sensitivity of detection means that only very small amounts of tracer need be added to follow the chemical pathway of the relevant species. Furthermore, it matters little what the physical or chemical state of the tracer is, for measurements may be made on liquids, solids or gases. Chromatography, solvent extraction and precipitation are amongst separation methods widely studied by means of radiotracers. In the individual separation steps the distribution of the species may be studied by simple radioactivity measurements, and subsequently the tracer will serve as a yield indicator for the overall procedure. 

Various technologies have been used to measure plasma lipids and lipoproteins and lipoprotein subfractions, including enzymatic, immunochemical, and chemical precipitation reagents, and physical methods, such as ultracentrifugation, electrophoresis, column chromatography, and others. Such methods have been reviewed extensively. As mentioned earlier, however, the cholesterol content of any particular lipoprotein class can vaiy somewhat from individual to individual. Moreover, although different methods of lipoprotein separation may produce similar lipoprotein fractions, they usually do not produce identical fractions, giving rise to systematic biases between methods that purport to measure the same component. The present discussion focuses primarily on methods and procedures commonly used in clinical practice for lipid and lipoprotein measurements. 

Substoichiometric separation is performed by ordinary chemical separation methods such as solvent extraction, ion exchange, precipitation, and electrochemical methods. In recent years, however, the ion exchange and electrochemical methods have not been used very much in substoichiometric separation. The precipitation technique is often used due to its simplicity, while solvent extraction is most widely employed. This is because the procedure for solvent extraction is very simple and an appropriate extraction system can usually be selected from the great number of research papers dealing with solvent extraction of many different elements. Two extraction systems are commonly used chelate extraction of metal ions with chelating agents and ion-association extraction of metal ions with simple negative or positive ions. 

Sometimes it is necessary to use separation and/or concentration procedures prior to spectrochemical analysis. Details of such procedures properly belong in texts on chemical separation and will not be dealt with here. However, some of the more common procedures that may be used include ashing of organic substances evaporation of solvent to concentrate the solute chemical precipitation ion exchange separations liquid-liquid extractions distillation and electrolysis. The selection of the method to be used will be determined primarily by the type of sample and the elements to be separated. 

Boron trifluoride catalyst may be recovered by distillation, chemical reactions, or a combination of these methods. Ammonia or amines are frequently added to the spent catalyst to form stable coordination compounds that can be separated from the reaction products. Subsequent treatment with sulfuric acid releases boron trifluoride. An organic compound may be added that forms an adduct more stable than that formed by the desired product and boron trifluoride. In another procedure, a fluoride is added to the reaction products to precipitate the boron trifluoride which is then released by heating. Selective solvents may also be employed in recovery procedures (see Catalysts,regeneration). 

The method of protein hydrolysis was important acid hydrolysis caused destruction of tryptophan but alkaline treatment gave even greater losses of other amino acids especially cystine. The amino acids were usually separated by then standard chemical procedures based on differences in solubility, selective precipitation by agents such as Reinecke salt (proline and hydroxyproline), or flavianic acid (arginine). 

As with covalently linked products it may be possible to isolate supramolecules because they separate from the reaction mixture as precipitates, crystals or oils. Some chemical work up procedures, such as liquid-liquid extraction or chromatography, may be required to achieve separation but the methods are usually akin to those widely used to isolate reaction products. Here there is little difference between conventional and supramolecular chemistry, however, the larger size of the supramolecules may make them less amenable to some conventional methods, crystallization in particular. 

In some cases, the most convenient method for the purification of a solid consists in precipitating it from a solution in which it is contained as a derivative. A typical example is the purification of a water-insoluble solid carboxylic acid by dissolving it in sodium hydroxide solution, filtering, and precipitating the compound by the addition of acid. A similar procedure may be used with amines dissolve the compound in acid and precipitate it with a base. These procedures usuallv work quite well in that they utilize a chemical reaction to aid in separation from nonacidic or nonbasic impurities. 

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