Chemical separation methods

Eor products having relatively low specific activity, such as some compounds labeled with and which are synthesized on the scale of several millimoles, classical organic chemical separation methods may be utilized, including extraction, precipitation, and crystallization. Eor separation of complex mixtures and for products having high specific activity, such as those labeled with tritium, etc, chromatographic methods utilizing paper, thin... 

The most important olefins and diolefins used to manufacture petrochemicals are ethylene, propylene, butylenes, and hutadiene. Butadiene, a conjugated diolefin, is normally coproduced with C2-C4 olefins from different cracking processes. Separation of these olefins from catalytic and thermal cracking gas streams could he achieved using physical and chemical separation methods. However, the petrochemical demand for olefins is much greater than the amounts these operations produce. Most olefins and hutadienes are produced hy steam cracking hydrocarbons. 

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. ... 

This chapter seeks to give the user of chemical separation methods the beginnings of a basis for understanding the methods described in this book and the ability to recognize normal behavior and to distinguish anomalous behavior . Justice to all the important theory would require several volumes of substantial size and especially if historical justice were to be given to the development of current models. At times the chapter s content will seem more conversational than hard scientific and the choice of style in any given instance, is deliberate. Stories are part of the history of separation methods, after all. 

Most, but not all, chemical separation methods are based on equilibrium in the sense of chemical equilibrium. Clearly, solubility is a chemical question but formation of a precipitate and filtration is a physical separation, which happens to use a favorable Ksp equilibrium... 

It is a great deal of work to actually determine a true equilibrium constant and most chemical separation methods speak in terms of values which are proportional to the actual equilibrium constant. At constant flow, the time that a given type of molecule is retained is related to the time for the void volume to pass after the sample is placed in a column or on a plate with the addition of the time for the net retention volume. If the flow remains constant, the temperature of the separation remains constant and no stationary phase is gained or lost, one can attempt qualitative identification using retention times. It is more reasonable to calculate the ratio of net retention volume to the void volume and call the result partition factor or capacity factor, k. ... 

Choppin, G.R. 1999. Overview of chemical separation methods and technologies. In Chemical Separation Technologies and Related Methods of Nuclear Waste Management Application, Problems and Research Needs. Choppin, G.R., Khankhasayev, M.Kh. Eds. Kluwer Academic, Netherlands, pp. 1-15. 

J. A. Dean, Chemical Separation Methods, Van Nostrand Reinhold, New York, 1969, p. 142. 

The expectation that superheavy elements will be detected by chemical and other identification procedures, even with these very small-cross sections, is now shifting to the heavy-ion accelerator laboratory (GSI) in Germany. There is the hope that the use of other heavy ions (including ions up to uranium) and greater beam intensities will lead to the synthesis and identification of superheavy elements. There are also several groups associated with GSI presently developing setups to detect superheavy elements using chemical separation methods similar to those described above as well as phase separations. 

The ideal chemical separation method should be relatively simple, have few separation stages and should be time / cost effective. Itoh et al (2002) used a combined anion and cation exchange column method for the isolation of Ca from other alkaline earth metals. This 3 column separation involved 6 chemical separation techniques following two HF/HCIO4 digests. The decontamination factors for Eu and Co are quoted as >10. The final limit of detection for " Ca for this method was 8 Bq/g, based on a measurement by X-ray spectrometric determination. 

The lead content of new and used gear oils can be determined by the chemical separation method (IP 120). However, there are a number of instrumental techniques that enable the results to be obtained very much more rapidly, among which are polarographic, flame photometric, and X-ray fluorescence methods. Chlorine can be determined by a chemical method as silver chloride (ASTM D-808) or by a titration method (ASTM D-1317, IP 118). 

Phosphorus in sediments can be divided into several different fractions according to chemical separation methods. Williams et al. (1976) outlined a scheme of three fractions apatite-P, organic P, and... 

Chromatography is the most versatile chemical separation method we have available at present. In it, a mixture is separated into various components on the basis of differences in the speed at which these components move through a chromatographic column. What differentiates their speeds is that the column slows them down by one mechanism or another. Many different retarding effects can be exploited, based on such diverse molecular properties as solubility, charge, size, adsorption, or biochemical affinity. Here we will consider partition chromatography, which is based on differences in (solvation) energy. 

U minerals and found the radioactive properties to be not a function of the physical or chemical forms of the uranium, but properties of the element itself. Using chemical separation methods, they isolated two new radioactive substances associated with the U minerals in 1898 and named them polonium and radium. In 1902 Ernest Rutherford and Frederick Soddy explained the nature of the process occurring in the natural decay chains as the radioactive decays of U and Th to produce new substances by transmutation. 

As shown in the lower pathway in f-igure 32-8. a destructive method requires that the analyte be separated from the other components of the sample prior to counting. If a chemical separation method is used, this technique is called radiochemical neutron activation. In this case a known amount of the irradiated sample is dissolved and the analyte separated by precipitation, extraction, ion exchange, or chromatography. The isolated material or a known fraction thereof is then counted for its gamma — or beta — activity. As in the nondestructive method, standards may be irradiated simultaneously and treated in an identical way. Equation. 32-21 is then used to calculate the results of the analysis. 

This means that the element of interest can be determined simply by measuring the radioactivity. The substoichiometric determination procedure consists of three steps radioisotopic labelling of the element of interest, reproducible separation of a fraction of the element of interest, and measurement of the radioactivity of the separated portion. In the first step, it is necessary to achieve an isotopic equilibrium between the element of interest and the added radioisotope. The x)nd step, known as substoichiometric separation, is the most important one. The absolute amount of the separated portions is not of concern a constant amount of the element of interest must be sejmrated with high reproducibility. The substoichiometric se mration is usually made by an appropriate chemical separation method. In solvent extraction, for example, this is made by adding a substoichiometric amount of reagent Miich is less than... 

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. 

As we noted that in most hydrogen-consuming or -producing reactions there is a separation of the isotopes. We became intrigued with the possibility of finding a chemical separation method which would not consume enormous quantities of electricity and could make deuterium and heavy water inexpensive. 

Distillation Most important chemical separation method, by which liquid or liquefied substances are separated from other (even solid) substances by evaporation and re-condensation... 

The chemical separation methods of activation analysis in which the radionuclides of interest are chemically isolated follow the schemes usually used in inorganic quantitative analysis. After the sample has been activated, it is decomposed or solubilized in the presence of a known weight of a nonradioactive chemical carrier, that is, a known amount of the stable element of interest. The addition of the carrier and the initiation of chemical reactions that permit an exchange of the radioactive and nonradioactive species is followed by a chemical isolation of the two species in a suitable stoichiometric form and the ultimate determination of the amount of carrier element (and thus the radioactive element) recovered. This type of separation does not need to be quantitative because the radioactivity measurements can be corrected for the measured yield of the carrier recovered from the chemical separation. 

Another favorite substance for medicine and cosmetics is menthol. It is obtained from a number of heibs, peppermint (Mentha x piperita L.) being the most common source (Fig. 2.13). The peppermint plant contains about 1-3 % essential oil, which can be obtained by a chemical separation method called steam distilla-tiom About half of the oil is menthol and its derivatives, terpenes, and flavonoids. Menthol has a pleasant odor and eooling effect, and these two properties are why... 

Gas chromatography (GC) is the premier chemical separation method for volatile compounds. It... 

After separation from excess reagent by any suitable chemical separation method like liquid-liquid distribution, chromatography, etc., the mass or concentration of this product is determined from activity measurement. 

Analyte Sample Preparation, Dissolution Chemical separation Method of measurement... 

Figure 2 Chemical separation methods for wafer samples.

---