Separation and enrichment

Separator GC/MS interface. An interface in which the effluent from the gas chromatograph is enriched in the ratio of sample to carrier gas. Separator, molecular separator, and enricher are synonymous terms. A separator should generally be defined as an effusion separator, a jet separator, or a membrane separator. 

Uranium hexafluoride is used in the gaseous diffusion process for the separation and enrichment of uranium-235, which exists in low concentration in natural uranium. The enriched UF is converted back into an oxide and used as fuel for the nuclear power industry. 

Koenig, K. H. Schuster, M. Steinbrech, B. Schneeweis, G. Schlodder, R. N,N-Dialkyl-N -benzoylthioureas as reagents for selective extractions for the separation and enrichment of platinum-group metals. Fresenius Z. Anal. Chem. 1985, 321, 457-460. 

The future will supposedly bring a more precise description of the trends considered here, and the reasons for the exceptions will be clearer. It is quite possible that in this field, too, the exceptions will only conhrm the rule. For now, it is worth concluding that all these regularities have very real practical applications. It is a fact that the equilibrium constants of the previously described reactions differ from unity. This provides an opportunity to separate and enrich isotopic mixtures. 

As the most important inorganic mass spectrometric technique, ICP-MS is also employed for the precise and accurate isotope ratio measurements of a multitude of elements (such as Li, B, S, Fe, Sr, Pb, U, Pu) in environmental samples (see Chapter 8).9,88-90 Isotope ratio measurements of environmental samples require special careful sample preparation techniques including trace/matrix separation and enrichment procedures if the analytes are at the trace and ultratrace level. As an example, the schematic diagrams of the separation and enrichment procedures for the precise isotope analysis of Pu, U and Sr in water samples from the Sea of Galilee using double-focusing... 

Figure 9.17 Schematic diagram of the separation and enrichment procedures for precise isotope analysis of Pu, U and Sr. (L. Halicz, J. 5. Becker et al. Int. J. Mass Spectrom., 249-250, 296 (2006). Reproduced by permission of Elsevier.)...

Another analytical procedure for sample preparation including analyte separation and enrichment is the coprecipitation of the trace elements to be determined. The co-precipitation behaviour of Ti, Mo, Sn and Sb under two different fluoride forming conditions (at < 70 °C in an ultrasonic bath and at 245 °C using a Teflon bomb) has been studied to improve the accuracy of the trace analysis of these elements in Ca-Al-Mg fluorides, by ICP-MS.14 The applicability of this analytical method (including isotope dilution technique) was demonstrated for four carbonaceous chondrites and silicate reference materials of basalt or andesite.14... 

Long-lived radionuclides occur at extremely low concentrations, especially in environmental samples, therefore several authors have proposed matrix separation and enrichment of the analytes before analysis.21,24,26,3 39 Radiochemical methods often require very careful and time consuming separation and enrichment processes and measurement procedures of a-, (3- and -emitting radioactive species at the trace and ultratrace level using conventional radioanalytical techniques 40-43 Trace/matrix separation, which is performed offline or online in order to avoid possible isobaric interferences, matrix effects and to reduce the detection limits for the determination of long-lived radionuclides, is also advantageous before ICP-MS measurements as the most widely applied mass spectrometric technique. 

As seen in Fig. 3.23, the absorption-desorption curves for H are different from those for D. This phenomena is used in types (3) and (4). By use of this phenomena, the separation of H and D, and enrichment of H and D from mixed gas are possible. The absorption-desorption curve for T (tritium) also differs from those for H and D thus we can separate and enrich H or D or T from the mixed gases by use of the absorption-desorption curves. D and T, which are used in nuclear reactors and nuclear fusion reactors, can be very efficiently separated and enriched by this principle. 

Liquid extraction FOR THE SEPARATION and enrichment of organic compounds in aqueous samples has been used successfully. Automated solvent extraction with flow-injection analysis has been reported (I). 

After the Marl of World War II he worked on the Manhattan Project at Columbia University with Nobel laureate Harold Urey. I.ibby was responsible lor the gaseous diffusion separation and enrichment of l ratiium-235 which was used in the atomic bomb nn Hiroshima. 

Among the numerous techniques for separating and enriching organic compounds from water samples, the following are worthy of mention solid-phase extraction (SPE), solid-phase microextraction (SPME), liquid-liquid extraction (LLE), and lyophilization. 

In SLM extraction, the transport mechanism is influenced primarily by the chemical characteristics of the analytes to be extracted and the organic liquid in the membrane into which the analytes will interact and diffuse. Analyte solubility in the membrane and its partition coefficient will have the main impact on separation and enrichment. Analyte transport in SLM extraction can be substantially categorized into two major types one is diffusive transport (or simple permeation) and the other covers facilitated transport (or carrier-mediated transport).73... 

Crust volatiles were isolated immediately after baking by extraction with dichloromethane and sublimation in vacuo ( ). Application of aroma extract dilution analysis 6) to the acid-free crust extract led to the detection of 31 odorants. After separation and enrichment, these compounds were identified by comparison of the MS/EI, MS/Cl and retention data on two columns of different polarity to reference compounds. Aroma quality was also assessed. The results of the identification experiments (Table I) revealed that 2(E)-none-nal (No. 1), followed by 2(E),4(E)-decadienal (No. 2) and 3-methyl-butanal (No. 3) showed the highest FD-factors in the crust of the chemically leavened bread. Additionally l-octen-3-one, 2(Z)-nonenal, 2(E),4(E)-nonadienal and an unknown compound with a metallic odor contributed high FD-factors to the overall flavor (For a discussion of FD-factors, see Chapter by Schieberle and Grosch, this book). 

This article surveys the research work on the synthesis and modification reactions of poly(ethyleneimine) as well as its applications to metal complexation processes. Poly-(ethyleneimine), one of the most simple heterochain polymers exists in the form of two different chemical structures one of them is branched, which is a commercially available and the other one linear which is synthesized by cationic polymerization of oxazoline monomers and subsequent hydrolysis of polyf(/V acylimino)cthylcne]. The most salient feature of poly(ethyleneimine) is the simultaneous presence of primary, secondary, and tertiary amino groups in the polymer chain which explains its basic properties and gives access to various modification reactions. A great number of synthetic routes to branched and linear poly(ethyleneimine)s and polymer-analogous reactions are described. In addition, the complexation of polyfethyleneimine) and its derivatives with metal ions is investigated. Homogeneous and heterogeneous metal separation and enrichment processes are reviewed. 

J. Messerschmidt, A. Von Bohlen, F. Alt, R. Klockenkamper, Separation and enrichment of palladium and gold in biological and environmental samples, adapted to the determination by total reflection X-ray fluorescence, Analyst, 125 (2000), 397D399. 

Based upon the use of nonionic surfactant systems and their cloud point phase separation behavior, several simple, practical, and efficient extraction methods have been proposed for the separation, concentration, and/or purification of a variety of substances including metal ions, proteins, and organic substances (429-441. 443.444). The use of nonionic micelles in this regard was first described and pioneered by Watanabe and co-workers who applied the approach to the separation and enrichment of metal ions (as metal chelates) (429-435). That is, metal ions in solution were converted to sparingly water soluble metal chelates which were then solubilized by addition of nonionic surfactant micelles subsequent to separation by the cloud point technique. Table XVII summarizes data available in the literature demonstrating the potential of the method for the separation of metal ions. As can be seen, factors of up to forty have been reported for the concentration effect of the separated metals. 

Kirkby N F (1986) In. Membranes m Gas Separation and Enrichment, Special Publication 62, Royal Society of Chemistry, London, p 221 Kiselev A V (1965) Disc Faraday Soc 40,205 Kiselev A V (1967) Adv Chromatogr 4,113... 

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