Separation by Chemical Methods

A brief survey of fast separation methods available nowadays was given by Trautmann [33]. An earlier survey was prepared by Kusaka and Meinke [145]. 

One important aspect for fast separations is the time needed to dissolve the target material. As long as solutions or very soluble salts can be irradiated the time will be rather small. However, in the case of charged particle induced reactions, metals are generally preferred as target materials due to their high heat conductivities as well as their mechani- 

Dissolving Agents Proposed for Common Target Materials (Metals, U Oq). 

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Problem 24.3 Outline the separation by chemical methods of a mixture of p-cresol,p-toluicacid,p-toluidine, andp-nitrotoluene. Describe exactly what you would da and see. 

Silver has also been used as the collector [5]. For metals such as Rh, Ir, and Os, good results have been obtained where iron, nickel, copper, tin, and their alloys are used as the collectors [6-8]. Tin [8] and copper [6,7] have also been used, instead of lead, in the separation of gold. If noble metals are separated along with metal collectors, the obtained alloys are dissolved in acid, and the noble metals are separated by chemical methods. Copper sulphide [9] and nickel sulphide [3,10-13] have also been recommended for the separation of noble metals. 

G.l (a) False. They can only be separated by chemical methods. 

The whole uranium work was completely reorganized early in December 1941. Lawrence took over the work on isotope separation by electromagnetic methods, Urey the isotope separation by chemical methods such as diffusion, centrifuging, etc, and Compton was assigned the methods of nuclear physics. Compton s work was to extend originally not only to the establishing of a nuclear chain reaction but also to the final use of the product. It will be seen that the second task was transferred around June 1942 to Oppenheimer s group. 

A recently defined and new objective has been trace element speciation, which provides information about the physical/chemical state of the trace elements. Species separated by chemical methods are subsequently determined by instrumental or radiochemical activation analysis. 

In the covalent approach, the imprinted molecule is covalently coupled to a polymerizable molecule. After copolymerization with crosslinker, the imprint molecule is separated by chemical method from the highly crosslinked polymer. The first MIP... 

The EO-PO ratio may also be determined by methods in which the polymer chains are cleaved by chemical methods. The EO and PO segments each yield different products that may be separated and quantified by gas chromatography [9,13]. Reagents used to effect this cleavage and the principal products obtained are given in Table 1 [14-17]. 

Heterogeneous catalytic systems offer the advantage that separation of the products from the catalyst is usually not a problem. The reacting fluid passes through a catalyst-filled reactor m the steady state, and the reaction products can be separated by standard methods. A recent innovation called catalytic distillation combines both the catalytic reaction and the separation process in the same vessel. This combination decreases the number of unit operations involved in a chemical process and has been used to make gasoline additives such as MTBE (methyl tertiai-y butyl ether). 

Bernard Manowitz, Treatment and Disposal of Wastes in Nuclear Chemical Technology George A. Sofer and Harold C. Weingartner, High Vacuum Technology Theodore Vermeulen, Separation by Adsorption Methods Sherman S. Weidenbaum, Mixing of Solids... 

Most of the time, enantiomers are found equally mixed together. Equally mixed enantiomers are not optically active because the rotation in one direction by one structure is canceled by the rotation in the opposite direction by the other structure. Hence, a sample of 2-butanol, for example, as normally obtained from a chemical vendor, is not optically active. An equimolar mixture of two enantiomers is called a racemic mixture and is optically inactive. Separation of a racemic mixture is not possible by conventional methods because the enantiomers are identical with respect to properties that are used to effect the separation. However, it may be possible to separate them by chemical methods, meaning that one may undergo a chemical reaction that the other does not. Some biological reactions are such reactions, and hence a single enantiomeric structure is sometimes found in nature. 

This method is very useful for separating amino acids found in food samples. The most effective matrix for separation is an absorbent cellulose-based filter paper. A very effective mobile phase is 70% isopropyl alcohol in water. Although the 20 amino acids are chemically very similar, they may be successfully separated by this method. Amino acids interact with the stationary phase to different extents, thus moving at different speeds. Chemical differences among amino acids that determine migration speed include molecular weight, charge, and polarity. 

Supercritical fluid extraction (SFE), microwave-assisted extraction (MAE) and Soxhlet extraction under various experimental conditions were applied for spiked poly(vinyl) chloride samples. Extracted dyes were separated in an ODS column (250 X 4.6 mm i.d. particle size 5 jum) using methanol as the mobile phase. Dyes are well separated by this method as demonstrated in Fig. 3.59. The optimal parameters of the extraction methods are compiled in Table 3.23. Recoveries depended on both the type of extraction method and the chemical structure of the dye. It was found that the highest recovery can be obtained by MAE and the extraction efficacy was the lowest for Solvent red 24 [129],... 

Chromatographic methods of separation are distinguished by their high selectivity, that is their ability to separate components of closely similar physical and chemical properties. Many mixtures which are difficult to separate by other methods may be separated by chromatography. The range of materials which can be processed covers the entire spectrum of molecular weights, from hydrogen to proteins. 

The lanthanide group of elements (Table 11.7) is very difficult to separate by traditional methods because of their similar chemical properties. The techniques originally used, like the precious metals, included laborious multiple fractional recrystallizations and fractional precipitation, both of which required many recycle streams to achieve reasonably pure products. Such techniques were unable to cope with the demands for significant quantities of certain pure compounds required by the electronics industry hence, other separation methods were developed. Resin ion exchange was the first of these... 

Salicylic acid and Its metabolite were separated by two methods. The first was thin layer chromatography on cellulose with BAW solvent as for the In vivo metabolism studies. A quicker separation was achieved with a polyamide column. The entire 400 pL from an individual assay was placed on top of a 0.8 x 2.0 cm column packed with Polyamide-6 (Accurate Chemical and Scientific Corp.). The salicylic acid metabolite was eluted with 6 mL water but salicylic acid was retained. 3a70B scintillation fluid (Research Product International Corp.) was used to determine the radioactive content of the entire 6 mL of eluant. Separation of salicylic acid and its metabolite by polyamide column chromatography was verified by thin layer chromatography. 

A majority of the chiral purity assays made with HPLC published during the last decade are based on separation on CSPs and subsequent UV detection (Table 17.3). The polysaccharide phases seem to be the dominating CSPs, but there is an even distribution in the methods that uses normal-and reversed-phase modes. A few of the methods utilize CMPA [39,59,60] or indirect separation by chemical derivatization [16,18]. However, it seems that the majority of the published papers... 

A. B. Gerber s process, cone, phosphoric acid is partially freed from arsenic, lead, lime, and fluorine by chemical methods, and is then subjected to a current of air at a temperature of 50° to remove volatile impurities. The suspended solids are then separated and the acid cooled, when crystalline phosphoric acid separates. 

A constant observation when the MRP were separated by various methods was that antioxidative effect was found in many different fractions. Both the dialysates and the retentates from dialysis were antioxidative to some extent. All the electrophoresis fractions exhibited some antioxidative effect. Attempts to separate the MRP by column chromatography on Sephadex G-50 have resulted in several fractions with some antioxidative effect, and so on. This indicates that several antioxidative products are formed by the Maillard reaction, possibly differing in molecular size and chemical structure, but perhaps with one single antioxidative functional group in common, such as a free radical function. However, it can not be excluded that the MRP contain a few entirely different antioxidants with different modes of action. Various mechanisms have also been suggested. Eichner (6) claimed MRP to inactivate the hydroperoxides formed by the lipid oxidation. There are also reports on the complex binding of metals by MRP (18, 19). 

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