Separation technique, zone

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

This separation technique has been employed primarily for preparative types of separations because detailed knowledge of the properties of the sample is required. Also, because this separation results in discrete zones of sample ions which are virtually pure, it makes sense to use this technique when the sample size is large. This technique is ineffective when the levels of impurities are small with respect to the target compound small amounts of sample ions do not form zones well and tend to mix with the target compound. Information on this technique is available (30). 

FIG. 18-122 Schematic of a rotary-drum vacuum filter with scraper discharge, showing operating zones. (Schweitzer, Handbook of Separation Techniques for Chemical Engineers, p. 4-38. Copqtight 1979 hq McGraw-Hill, Inc. Used with permission of McGraw-Hill Inc.)... 

Electrodriven Separation Techniques encompass a wide range of analytical procedures based on several distinct physical and chemical principles, usually acting together to perform the requh ed separation. Example of electrophoretic-based techniques includes capillary zone electrophoresis (CZE), capillary isotachophoresis (CITP), and capillary gel electrophoresis (CGE) (45-47). Some other electrodriven separation techniques are based not only on electrophoretic principles but rather on chromatographic principles as well. Examples of the latter are micellar... 

In Chapter 7, approaches for visualization of zones in chromatograms are discussed, including use of nondestructive and destructive dyeing reagents, fluorescence quenching on layers with a fluorescent indicator, and densitometry. In Chapter 8, additional detection methods, such as those used for biologically active and radioactive zones, as well as the recovery of separated, detected zones by scraping and elution techniques are covered. 

Another separation technique utilizes an electric field. An electric held is an electrically charged region of space, such as between a pair of electrodes connected to a power supply. The technique utilizes the varied rates and direction with which different organic ions (or large molecules with charged sites) migrate while under the influence of the electric held. This technique is called electrophoresis. Zone electrophoresis refers to the common case in which a medium such as cellulose or gel is used to contain the solution. A schematic diagram of the electrophoresis apparatus resembles an electrochemical apparatus in many... 

Zonal techniques are the most frequently used form of electrophoresis and involve the application of a sample as a small zone to a relatively large area of inert supporting medium which enables the subsequent detection of the separated sample zones. A wide range of supporting media have been developed either to eliminate difficulties caused by some media (e.g. the adsorptive effects of paper) or to offer additional features (e.g. the molecular sieving effects of polyacrylamide gel). 

One of the major advantages of CE as a separation technique is the wide variety of separation modes available. Analytes can be separated on the basis of charge, molecular size or shape, pi, or hydrophobicity. The same CE instrument can be used for zone electrophoresis, IEF, sieving separations, isotachophoresis, and chromatographic techniques such as MEKC and capillary electrokinetic chromatography. This section provides a brief description of each separation mode. Zone electrophoresis, IEF, and sieving are the primary modes used for protein separations, and these will be discussed in detail in the following sections. 

Reilly, J., and Saeed, M. (1998). Capillary electrochromatography as an alternative separation technique to high-performance liquid chromatography and capillary zone electrophoresis for the determination of drug related impurities in Lilly compound LY300164. /. Chromatogr. A 829, 175-186. 

Dedicated applications of capillary zone electrophoresis (CZE) coupled to MS are discussed, particularly in the field of drug analysis. Development of other capillary-based electrodriven separation techniques such as non-aqueous capillary electrophoresis (NACE), micellar electrokinetic chromatography (MEKC), and capillary electrochromatography (CEC) hyphenated with MS are also treated. The successful coupling of these electromigration schemes with MS detection provides an efficient and sensitive analytical tool for the separation, quantitation, and identification of numerous pharmaceutical, biological, therapeutic, and environmental compounds. 

Fines removal. The annular zone enables a sharp separation to be made because of the low solids concentration which prevails in the upper part of this zone. Furthermore, it is a simple separation technique and, as such, is very successful. As a result of the low cut size, its effect on the average size produced in the crystalliser is negligible. At a higher solids concentration a reasonable separation is also attained using the hydrocyclone. 

Capillary zone electrophoresis is a separation technique that benefits from very high efficiency, not selectivity. This is in contrast to chromatography, for which the converse is true. Differences in mobility in the range of 0.01% can be enough for complete resolution of neighboring peaks. The resolution R is defined as... 

Capillary zone electrophoresis (CZE) is the most common electrophoretic separation technique due to its simplicity of operation and its flexibility. It is the standard mode for drug analysis, identification of impurities, and pharmacokinetic studies. Other separation modes, such as capillary isotachopho-resis (CITP), micellar electrokinetc chromatography (MEKC), capillary electrochromatography (CEC), capillary gel electrophoresis (CGE), capillary isoelectric focusing, and affinity capillary electrophoresis (ACE), have then-advantages in solving specific separation problems, since the separation mechanism of each mode is different. 

---