Separation technique

Ion exchange membranes are widely used in electrodialysis and other membrane separation techniques. Perfluorosulphonic membranes are much less used in this area because of their high cost. For separation techniques, less expensive membranes may be used because the physical conditions and the chemical environment are less drastic than in the chlor-alkali electrolysis or the various SPE applications. 

The use of Nafion membrane as a proton conductor has been mentioned in a three-compartment electrodialysis set-up for converting sodium salicylate to salicylic acid . Use in Donnan analysis for the recovery of Cu ions from dilute solutions has been described . These metal ions are transferred through the membrane. The driving force is the proton-motive force resulting from the proton concentration difference between the two sides of the membrane. The diffusion flux of protons is coupled to a counter-transport of metal ions. 

The task of quantitative and effective separation of small amounts of radionuclides has appreciably enhanced the development of modem separation techniques. High radionuclide purity is of great importance for application in nuclear medicine as well as for sensitive measurements. In this context, impurities of long-lived radionuclides arc of particular importance, because their relative activity increases with time. For example, if the activity of Sr is only 0.1% of that of Ba after fre.sh separation, it will increase to 11.5% in three months. 

If coprecipitation of radionuclides present in low concentrations is to be avoided, hold-back carriers are added. Isotopic carriers are most effective foi this purpose, but they lead to low specific activity. 

For filtration, Hahn suction filters arc convenient (Fig. 12.6). They allow easy removal of the filter for further operations or subsequent measurements. 

Electrolytic deposition of radionuclides is frequently applied. It gives thin. samples and is well suited for preparation of standard samples. For instance, Po, Pb or Mn can be dcpo.sited with high yields on anodes of Cu, Pt or Ag, and by electrolysis of the nitrates or chlorides of Th and Ac in acetone or ethanol solutions these elements can be separated on cathodes. The preparation of thin samples by electrolytic deposition is of special interest for the measurement of a emitters, such as isotopes of Ihi or other actinides. 

Separation of radionuclides by distillation is applicable if volatile compounds arc formed. Separation of from irradiated Tc has already been mentioned in section 12.1. Other examples are separation of Ru as R11O4 under oxidizing conditions, and volatilization of Tc as TC2O7 from concentrated H2SO4 at 150-250 C. -P may be purified by volatilization as PCI5 in a stream of CE. 

In the previous chapter on sample preparation for chromatographic analysis the principal objective has been to secure dissolution of analytes in a suitable solvent and removal from the solution of as many interfering compounds as possible. General sample handling 

Additives In Polymers Industrial Analysis And Applications J. C. J. Bart 2005 John Wiley Sons, Ltd ISBN 0-470-85062-0 

Boundaries in chromatography and extraction are blurring, as evident from the relation between GC, SFC and HPLC, the use of superheated/subcritical water for extraction and chromatography, and the role of enhanced fluidity solvents and pressurised fluid extractions [2]. Extraction is an extreme form of chromatography. Separation science recognises that there is unity in the 

The physical properties of the mobile phase, mainly viscosity, diffusivity and solubility, affect the flow characteristics, column efficiency (kinetics), and retention (thermodynamics) in the chromatographic process. These physical properties are affected by temperature. Chromatographic techniques, although basically simple in 

Mobile phase Gas, SCF, liquid, ionic solution Pressure, density Single vs. multiple component Polar vs. nonpolar 

Each band seen in the gel represents a different oligonucleotide. 

Human chromosomes viewed through a scanning electron microscope. 

What is the purpose of genetic engineering How can human proteins be made by bacteria What is an expression vector  

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After the DNA pieces have been separated, they must be treated in some way that allows them to be seen. Some of these techniques allow all of the DNA to be seen, but others are more specific for certain DNA pieces. 

The soluble polymeric supports presented in this chapter will be classified according to their topology, which strongly influences the physical properties of these materials. There are three major classes (i) endgroup-functionaUsed linear polymers, (ii) linear polymers which contain a reactive group in every monomer unit and (iii) starpolymers and branched structures like hyper-branched polymers and dendrimers. 

One of the major benefits of polymer-supported catalysis is the recovery and the reuse of immobihsed catalysts, especially when dealing with chiral catalysts which can be extremely expensive [17]. Therefore effective separation methods are required [1]. However, one has to keep in mind that even the best separation technique can t overcome all the problems that can occur in polymer-sup-ported catalysis. For example, metal leaching is one major problem associated with the use and the recycHng of metal-based, polymer-supported catalytic systems and often the addition of fresh metal species to the recovered catalysts is 

Parameter Dialysis Ultra- filtration SEC Precipitation/ filtration Liquid-phase separation 

Separation by Hydro-dynamic volume Hydro- dynamic volume Hydro- dynamic volume Solubility Solubility 

Limitations Only suitable for polymer isolation Coprecipitation of impurities possible Clear phase separation required 

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In order to simplify the analysis of petroleum and its fractions, other preliminary separation techniques are employed, aiming generally to separate certain classes of components. 

Liquid chromatography is a separation technique based on the selective adsorption on a solid, siiica or alumina for example, or a mixture of the two, of the different components of a liquid mixture. 

R. Lemlich, ed.. Adsorptive Bubble Separation Techniques, Academic, New York, 1972. 

D. W. Fuerstenau and T. W. Healy, Adsorptive Bubble Separation Techniques, Academic Press, 1971, p. 92 D. W Fuerstenau, Pure Appl. Chetn., 24, 135 (1970). 

The element may be obtained by separating neodymium salts from other rare earths by ion-exchange or solvent extraction techniques, and by reducing anhydrous halides such as NdFs with calcium metal. Other separation techniques are possible. 

Many precipitation reactions that are useful as separation techniques for gravimetric analysis fail to meet one or both of two requirements for titrimetry ... 

An analyte and an interferent can be separated if there is a significant difference in at least one of their chemical or physical properties. Table 7.4 provides a partial list of several separation techniques, classified by the chemical or physical property that is exploited. 

The simplest physical property that can be exploited in a separation is size. The separation is accomplished using a porous medium through which only the analyte or interferent can pass. Filtration, in which gravity, suction, or pressure is used to pass a sample through a porous filter is the most commonly encountered separation technique based on size. 

Particulate interferents can be separated from dissolved analytes by filtration, using a filter whose pore size retains the interferent. This separation technique is important in the analysis of many natural waters, for which the presence of suspended solids may interfere in the analysis. Filtration also can be used to isolate analytes present as solid particulates from dissolved ions in the sample matrix. For example, this is a necessary step in gravimetry, in which the analyte is isolated as a precipitate. A more detailed description of the types of available filters is found in the discussion of precipitation gravimetry and particulate gravimetry in Chapter 8. 

The most important class of separation techniques is based on the selective partitioning of the analyte or interferent between two immiscible phases. When a phase containing a solute, S, is brought into contact with a second phase, the solute partitions itself between the two phases. 

Extraction Between Two Phases When the sample is initially present in one of the phases, the separation is known as an extraction. In a simple extraction the sample is extracted one or more times with portions of the second phase. Simple extractions are particularly useful for separations in which only one component has a favorable distribution ratio. Several important separation techniques are based on simple extractions, including liquid-liquid, liquid-solid, solid-liquid, and gas-solid extractions. 

Two frequently encountered analytical problems are (1) the presence of matrix components interfering with the analysis of the analyte and (2) the presence of analytes at concentrations too small to analyze accurately. We have seen how a separation can be used to solve the former problem. Interestingly, separation techniques can often be used to solve the second problem as well. For separations in which a complete recovery of the analyte is desired, it may be possible to transfer the analyte in a manner that increases its concentration. This step in an analytical procedure is known as a preconcentration. 

In Chapter 7 we examined several methods for separating an analyte from potential interferents. For example, in a liquid-liquid extraction the analyte and interferent are initially present in a single liquid phase. A second, immiscible liquid phase is introduced, and the two phases are thoroughly mixed by shaking. During this process the analyte and interferents partition themselves between the two phases to different extents, affecting their separation. Despite the power of these separation techniques, there are some significant limitations. 

A separation technique in which the mobile phase is a supercritical fluid. 

A separation technique based on a solute s ability to move through a conductive medium under the influence of an electric field. 

GC and LC (or HPLC) are two of the most widely used separation techniques in chemistry, biochemistry, pharmacology, and medical and environmental sciences. 

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