Electrokinetics advantages

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. 

Sample preconcentration techniques are used with two purposes (1) to increase concentration in order to achieve detection and (2) to eliminate disturbances of the electrophoretic system during hydraulic or electrokinetic sample introduction when the conductivity of the sample is significantly different from that of the analysis buffer. It is important to keep sample manipulations and modifications to a minimum, and a rule of thumb is to prepare the sample so that its composition is at the same pH as the analysis buffer. It is also advantageous... 

There are two main injection strategies for CE, electrokinetic and pressure. Each type of injection mode has its advantages and disadvantages. Depending on the application, the appropriate mode must be chosen. 

Micellar electrokinetic chromatography is applied for the analysis of a wide variety of organic substances, ionic and nonionic in nature. For instance, for the determination of the content of active pharmaceutical ingredients in tablets, creams, and injectables, the MEKC mode often offers advantages over the CZE mode. 

According to the Interstate Technology and Regulatory Cooperation Work Group, the electrokinetic decontamination process has the following advantages ... 

The major advantage of protein adsorption studies on high surface area materials is that changes of some extensive properties which accompany the process of adsorption are large enough to be directly measured heat of adsorption through microcalorimetry 141), uptake or release of small ions by a combination of electrokinetic methods and titration 142), thickness of adsorbed layer or an increase of the volume fraction of solid phase by a hydrodynamic method like viscometry 143). Chromatographiclike analysis can also be applied to protein adsorption 144). 

Microemulsion electrokinetic chromatography, MEEKC (or MECC), is a relatively new technique which holds some promise of delivering octanol/water partition coefficients much more conveniently than the shake-flask method (Gluck, 1996 Ishihama, 1994). MEEKC is claimed to have all the advantages of an HPLC method but it is not suitable for solutes with pKas much below 7.0 (Adlard, 1995). It has been used over a log P range of -1.0 to +4.0. 

Capillary electrophoresis (CE) coupled to MS has the advantage of high resolution and soft ionization for biomolecules, which may be used to differentiate post-translational modifications and variants of intact proteins and oligonucleotides. Different modes of CE (capillary zone electrophoresis, capillary isoelectric focusing, capillary electrochromatography, micellar electrokinetic chromatography, nonaqueous capillary electrophoresis) to MS as well as online preconcentration techniques (transient capillary isotachophoresis, solid-phase extraction, membrane preconcentration) are used to compensate for the restricted detection sensitivity of the CE methodology [77, 78]. 

The early phase of development can be characterized by a transfer of concepts from conventional CE to the planar format, such as capillary gel electrophoresis, micellar electrokinetic chromatography, sample stacking and pre- and postcolumn sample derivatization. Emphasis was laid on the demonstration of the specific advantages mainly from the separation science point of view. With only very few exceptions, detection has received much less attention yet. LIF detection with confocal imaging has been used in most of the early work owing to its high sensitivity and its relatively easy implementation. If not explicitly mentioned otherwise, all experiments described in the following sections were carried out with LIF detection [28,29]. 

A major advantage of capillary gel electrophoresis is that resolution is maintained with increasing field strength, owing to efficient heat dissipation. Introduction of the sample into the gel-filled capillary is typically done electrokinetically (Chapter 6), because hydrostatic injection is not possible with capillaries blocked with gel. Typical injection times between 1 and 20 sec are used at field strengths between 100 and 400 V/cm.28 Coated capillaries should be used to prevent the EOF from pumping the gel out of the capillary. 

The introduction of the samples onto the capillary column can be carried out by either displacement techniques or electrokinetic migration. Three methods of displacement or hydrostatic injection are available a) direct injection, or pressure b) gravity flow, or siphoning and c) suction. The electrokinetic injection method arose from findings that electroosmosis act like a pump (80). Both methods have advantages and disadvantages. For example, a bias has been reported in electrokinetically injected... 

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