Capillary electrophoresis separation techniques

In the 1980s, a new separations technique, capillary electrophoresis (CE), was developed. CE created great excitement and was initially expected to replace HPLC as the method of choice for ultratrace analyses. However, it became evident that CE was complementary to HPLC and filled a different niche in separations. Since each technique has advantages and disadvantages, it is important to understand the basic theory that underlies the separations in order to choose the right technique for a problem. 

Chiral additives have been shown to be very effective for chiral separations by capillary electrophoresis (CE) [4, 5]. Indeed, it may be argued that there has been considerably more research activity in chiral separations by CE than by EC methods since the introduction of the former technique. Chiral additives in CE have several advantages, some of which are highlighted in Table 11-2. 

Capillary electrophoresis is a general term that is used to describe a number of different separation techniques. Capillary zone electrophoresis (CZE) is the classic technique and is therefore usually referred to as just CE. Other techniques include micellar electrokinetic chromatography (MEKC), capillary isoelectric focusing, and capillary isotachophoresis. CZE and MEKC are the predominant techniques and are those used herein, so only they will be discussed in detail here. 

Synthetic polyelectrolytes can be separated by capillary electrophoresis applying the same rules derived for the electrophoresis of biopolymers. In the reptation regime, determination of the molecular mass and polydispersity of the polyelectrolytes is possible. Introduction of chromophores facilitates the detection of non-UV-absorbing polymers. Indirect detection techniques can probably be applied when analytes and chromophores of similar mobilities are available. 

Modern techniques usually consist of so-called hyphenated techniques, which means the combination of a separation step [capillary electrophoresis (CE), high-performance liquid chromatography (HPLC), etc.] and the element-specific determination using electrochemical detectors or spectrometric techniques. The use of ICP-MS as the element-specific detector has gained frequent application (reviewed in Barefoot 1999, 2001 Timerbaev et al. 2002). 

Product analysis of irradiated samples attains the ppb level and separation of geometrical isomers is routinely performed. Using gel permeation chromatography the product distribution of y-irradiated n-alkanes has been recently mapped (50). As can be seen in Figure 2, unprecedented resolution of the various isomers can now be achieved with modern chromatographic techniques. Capillary electrophoresis is presently used to determine the product distribution of various cresols and yields as low as 0.1 molecules/100 eV are routinely measured (51). 

Lin Y W, ChiuT C, Chang HT (2003). Laser-induced fluorescence technique for DNA and proteins separated by capillary electrophoresis. J. Chromatog. B. 793 37-48. 

The devices based on microfluidic chip-capillary electrophoresis (microchip-CE) make use of the microfluidic chip technology for sample preparation and pretreatment prior to highly efficient separation by capillary electrophoresis using commercially available instrumentation. A list of the research and development work performed using the hyphenated microfluidic chip-CE technique is given in Table 2, showing three major areas of application. 

Size separations by capillary electrophoresis (CE) are performed using low viscosity and replaceable linear polymer solutions. Tbe technique was employed for DNA sequencing during the Human Genome Project, which was completed in 2000. Current applications involve many modes of DNA separation as well as those involving sodium dodecyl sulfate (SDS) proteins. The purity of recombinant monoclonal antibodies is often determined using CE. 

Usually, sample analysis combines the use of different analytical techniques, such as spectroscopic (MS (mass spectrometry), NMR (nuclear magnetic resonance), IR (infra-red), FL, among others), electrochemical (voltammetry, conduc-timetry), separation (CE [capillary electrophoresis], GC [gas chromatography], LC [liquid chromatography]), or hyphenated techniques. All of them have been applied, to a greater or lesser extent, for food analysis [88]. As can be seen in Table 8.1, the... 

A relatively new technique, capillary electrophoresis (CE) is becoming increasingly recognized as an important analytical separation technique. It has the advantage of... 

The individual separation, identification, and quantification of OL derivatives from natural extracts have been realized basically by chromatographic separation or capillary electrophoresis methods. Both gas and liquid chromatographies have been exploited, combined with several detection methods such as UV, fluorescence, and mass spectrometry (MS) [14], Soft spectroscopic techniques as midium infrared spectroscopy have been recently explored for rapid quantification of OL [61], while high-resolution spectroscopic techniques as nuclear magnetic resonance are considered interesting applicatimi in the analysis of the OL derivative structures [14]. 

Capillary Electrophoresis Because of its remarkable separation capabilities, capillary electrophoresis has been rapidly developed for use in biotechnology, particularly in gene splicing. In this technique a capillary tube of glass is used. The capillary is immersed in electrolyte-filled reservoirs containing electrodes... 

Capillary Electrophoresis. Capillary electrophoresis (ce) or capillary 2one electrophoresis (c2e), a relatively recent addition to the arsenal of analytical techniques (20,21), has also been demonstrated as a powerful chiral separation method. Its high resolution capabiUty and lower sample loading relative to hplc makes it ideal for the separation of minute amounts of components in complex biological mixtures (22,23). 

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). 

Capillary Electrophoresis. Capillary electrophoresis (ce) is an analytical technique that can achieve rapid high resolution separation of water-soluble components present in small sample volumes. The separations are generally based on the principle of electrically driven ions in solution. Selectivity can be varied by the alteration of pH, ionic strength, electrolyte composition, or by incorporation of additives. Typical examples of additives include organic solvents, surfactants (qv), and complexation agents (see Chelating agents). 

The heating effect is the limiting factor for all electrophoretic separations. When heat is dissipated rapidly, as in capillary electrophoresis, rapid, high resolution separations are possible. For electrophoretic separations the higher the separating driving force, ie, the electric field strength, the better the resolution. This means that if a way to separate faster can be found, it should also be a more effective separation. This is the opposite of most other separation techniques. 

One of the important problems in the diagnosis of different disease in their early stages is the determination of bio-active substances in biological fluids. We are currently interested in applying capillary electrophoresis (CE) as technique for the rapid and highly efficient separation of corticosteroids in semm and urine. Steroids can analyze by MEKC. 

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... 

This chapter will first cover the nature of electrophoretic separations, especially those concerning capillary electrophoresis. Comprehensive multidimensional separations will then be defined, specifically in terms of orthogonality and resolution. The history of planar and non-comprehensive electrodriven separations will then be discussed. True comprehensive multidimensional separations involving chromatography and capillary electrophoresis will be described next. Finally, the future directions of these multidimensional techniques will be outlined. 

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