Separation Principles and

H. Axelsson, Centrifugal Separations—Principles and Techniques, Alfa Laval Separation, Tumba, Sweden, presented at the Bioprocess Technology Program, University of Virginia, Charlottesville, Va., Oct. 17—25 1991. 

There are two ways to classify liquid chromatographic methods. The first and more common classification is based on the mechanism of retention, and from this the chromatographic modes discussed in Chapter 2 are derived. For example, the normal-phase mode can be performed by taking advantage of either the adsorption mechanism or the partition mechanism. The gel-filtration mode is performed using the mechanism of size exclusion. The second classification discussed below is based on the separation principle and is found mostly in the literature published before the 1990s. 

Usually bi- or multi-dimension separations must be run individually since they utilize different physico-chemical separation principles and differ greatly in selectivity. Ion-pairing and electrophoretic mobility provide two compatible separation models that may be run simultaneously in the same single separation device to achieve a bi-dimensional technique. Since they are respectively based on the complex hydrophobicity and on the analyte change, experiments demonstrated that ion-pairing... 

Eriez, Magnetics Europe Ltd., Eddy Current Separators, Principle and Practice , Brochure No SB 501 UK, p. 1. 

Enantiomer separation becomes very easy when a column with a solid chiral stationary phase (CSP) able to separate a given enantiomer pair is available. Unfortunately, there is no universal phase for solving all separation problems and it is impossible that there ever will be. However, an immense number of CSPs have been developed and many of them are commercially available. A good deal of literature has also been published, from which a promising phase can usually be selected. Sometimes, the sample can be adapted to the phase by nonchiral derivatization. The most important CSPs are listed in Table 22.1. They are based on very different separation principles and can be grouped as follows ... 

A commercial CE system and a micropacked capillary was used to separate N—, O—, and S-containing heterocyclic compounds. Migration time reproducibility, linearity, and detector response was found to be comparable to HPLC. A study of the heterocyclic compound s elution order followed that predicted by the octanol-water partition coefficients (354). While chiral CEC provides improved resolution and higher efficiencies, additional work is needed since chiral CEC capillaries are not available commercially. The separation principles and chiral recognition mechanism for the separation of enantiomers have been reviewed (355). Furthermore, a comprehensive collection of drug applications and other compounds of interest has been reported (356). Direct enantiomeric separations by CEC were studied using a capillary packed with alpha-1-acid glycoprotein chiral stationary phase (357). Chiral resolution was achieved for enantiomers of benzoin, hexobarbital, pentobarbital, fosfamide, disopyramide, methoprolol, oxprenolol, and propanolol. The effects of pH, electrolyte concentration, and con-... 

Dunlop EC (1961) Decomposition and dissolution of samples organic. In Kolthoff IM, Elving PJ and Sandell EB, eds. Treatise on analytical chemistry. Part I (Theory and practice), Vol 2, section C. Separation principles and technics (LB Rogers, section advisor), pp. 1051-1094. Interscience Publishers, New York. 

FI methods of separation and preconcentration exhibit some extremely favourable features over their batch or even continuous flow counterparts. The general merits summarized below are alid, irrespective of the separation principles and equipment involved ... 

Table 3.2. A number of modes of capillary electrophoresis with their commonly used abbreviations, separation principle and applications.

After a long deliberation, the inventor has decided to use the time separation principle and has chosen to deliver sandwiches exactly when they are needed by means of helicopter drones. As a temporary measure, she will first use the communication drones that are already in use to carry confidential messages among the support team members. Later, special stealth helicopter drones will be ordered (and invented first), which be invisible to other teams and which will fly silently. 

The underlying separation principles and many of the techniques developed and used at that time are essentially the same as those in use today. 

Desalination of (sea)water is an illustrative example of a separation problem for which competitive separation processes, based on different separation principles and consunung different amounts of energy, can be used. 

Although the driving forces, the. separation principle and the membranes are completely different in elecirodialysis from those in pressure-driven membrane processes, polarisation phenomena may severely aflect the separation efficiency. 

In comparison to isothermal membrane processes, little attention has been paid to date to polarisation phenomena in non-isothermal processes. In non-isothermal processes such as membrane distillation and thermo-osmosis, transport through the membrane Occurs when a temperature difference is applied across the membrane. Temperature polarisation will occur in both membrane processes although both differ considerably in membrane structure, separation principle and practical-application. In a similar manner to concentration polarisation in pressure-driven membrane processes, coupled heat and mass transfer contribute towards temperature polarisation. 

Taking first the separation by particle size, this is clearly based on the size dependent nature of some sohd—hquid separation principles and equipment... 

Unfortunately, SEC has a narrow separation window due to the limitation of the distribution coefficient. The peak capacity is lower than with other HPLC separation principles, and typical values are in the range of 10-20. 

Size exclusion chromatography (SEC) has been widely used since its introduction during the 1960s. It offers a simple yet unbiased method to characterize the molecular weight distribution of a polymer. Although it uses a flow system, the separation principle and the analysis are based on a static property of the polymer molecules in solution. We briefly look at the separation system here before learning the principle. 

Once the student is introduced to basic concepts, consumer applications and environmental problems follow. The text, however, does not separate principles and applications. Early chapters involving basic principles also contain applications, and later chapters with more emphasis on applications build on and expand basic principles. 

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