Modes of capillary

Fan et al. [106] developed a high performance capillary electrophoresis method for the analysis of primaquine and its trifluoroacetyl derivative. The method is based on the mode of capillary-zone electrophoresis in the Bio-Rad HPE-100 capillary electrophoresis system effects of some factors in the electrophoretic conditions on the separation of primaquine and trifluoroacetyl primaquine were studied. Methyl ephedrine was used as the internal standard and the detection was carried out at 210 nm. A linear relationship was obtained between the ratio of peak area of sample and internal standard and corresponding concentration of sample. The relative standard deviations of migration time and the ratio of peak area of within-day and between-day for replicate injections were <0.6% and 5.0%, respectively. 

Several modes of capillary electrophoretic separation are available ordinary CE, capillary zone electrophoresis, capillary electrokinetic chromatography, capillary gel electrophoresis, capillary electrochromatography, capillary isota-chophoresis, and capillary isoelectric focusing. The different separation mechanisms make it possible to separate a wide variety of substances depending on their mass, charge, and chemical nature.53... 

The origins, principles, methods, and modes of capillary electrophoresis (CE) are discussed. Massive application of electrophoresis methods started after Tiselius s moving boundary method that was optimized by the use of paper or a gel as a semiconducting medium. The applications of paper and gel electrophoresis were situated mostly in the biochemical environment for the analysis of proteins, amino... 

After a short introduction into the relevance of Impurity profiling for regulatory authorities, public health, and the pharmaceutical industry, an overview is presented based on the various modes of capillary electrophoresis that have been used in drug impurity analysis. The applications of capillary zone electrophoresis, non-aqueous capillary electrophoresis, micellar electrokinetic capillary chromatography, microemulsion electrokinetic capillary chromatography, capillary gel electrophoresis, and capillary electrochromatography are presented consecutively. 

The separation scientist with experience gained from a LC background may tend to limit the modes of electrochromatography to reversed phase (RP), normal phase, ion-exchange and, maybe, size-exclusion. Analysts from an electrophoretic background typically use the term "CE" in a much broader sense to include the main modes of capillary zone electrophoresis, micellar electrokinetic chromatography, capillary gel electrophoresis, isoelectric focusing and isotachophoresis. 

Table 1 The Four Main Modes of Capillary Zone Electrophoresis, Characterized by the Signs and Limiting Values of the Key Migration Parameters3...

Capillary isoelectric focusing (CIEF) is one of the modes of capillary electrophoresis which relies on a separation of amphoteric solutes with different iso-... 

Amino adds, peptides, and proteins are analyzed by a variety of modes of capillary electrophoresis (CE) which employ the same instrumentation, but are different in the mechanism of separation. A fundamental aspect of each mode of CE is the composition of the electrolyte solution. Depending on the specihc mode of CE, the electrolyte solution can consist of either a continuous or a discontinuous system. In continuous systems, the composition of the electrolyte solution is constant along the capillary tube, whereas in discontinuous systems, it is varied along the migration path. 

Even though capillary electrophoresis is a relatively simple method, several formats exist that allow for analyses of different types of samples or to take advantage of certain solute properties. The primary modes of capillary electrophoresis are as follows ... 

Boone, C.M. Douma, J.W. Franke, J.P. de Zeeuw, R.A. Easing, K. Screening for the presence of drugs in serum and urine using different separation modes of capillary electrophoresis. Forensic Sci. Int. 2001, 121, 89-96. 

Peterson, J. R. Mohammad, A., Eds. Basic Principles and Modes of Capillary Electrophoresis, Humana Press Totowa (NJ), 2001. 

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

Similarly to gel electrophoresis, a number of modes can be employed that separate analyte mixtures according to different properties. Some of these modes are summarised in Table 3.2 together with their commonly used abbreviations. Depending on the principle of separation, different species can be analysed. After an overview of capillary electrophoretic instrumentation, the different modes of capillary electrophoresis are described in more detail including capillary zone electrophoresis (CZE), capillary isoelectric focussing (CIEF), micellar electro-kinetic chromatography (MEKC) and capillary gel electrophoresis (CGE). 

F. Regan, A. Moran, B. Fogarty and E. Dempsey, Novel modes of capillary electrophoresis for the determination of endocrine disrupting chemicals, J. Chromatogr. A, 1014,141-152, 2003. 

Almost all operational modes of capillary electrophoresis have been combined with mass spectrometry via CF-FAB [68-70], MALDI [57,71], and ESI [72-76]. Of these three technologies, ESI has attained an enviable status as the interface of choice to couple CE with mass spectrometry. A CE/MS interface must address the problem of the low liquid flow rates of the CE process. Other considerations are buffer compositions and electrical contact between the separation buffer and the interface. As with LC/MS systems, only volatile buffers are tolerated in a CE/MS operation. Also, high salt concentrations must be avoided for stable operation of a mass spectrometry system. 

During the last decades the different modes of capillary electrophoresis (CE) have developed into high-performance (HPCE) separation methods, offering a high separation efficiency (lO -lO theoretical plates), high sensitivity (femtomole to zeptomole amounts in nano- to picoliter sample volumes), and short analysis times (typically 5-20 min, in special cases only a few seconds). They are considered as a recognized complement and/or coimterpart of liquid chromatography (LC) and gel electrophoretic methods. 

Especially outstanding separation of 10 MC variants has been reported in MEKC mode of capillary electrophoresis with UV detection.This is preferable method for electrophoretic determination of MC as their separation can be impeded by adsorption of analytes onto the capillary wall, hence separation conditions in basic media with micelles should prevent such interaction. As BGE for such separation 40 mM (3-(cyclohexylamino)-l-propanesulfonate buffer of pH 10.6, containing acetate and 15 mM sodium dodecyl sulfate (SDS), was used and UV detection was carried out at 238 nm. The electropherogram obtained for a mixture of MC isolated with a preparative HPLC from cyanobacterial Anahaena 90 strains is shown in Eig. 5. 

There are several modes of capillary electrophoresis, some of which combine electropheretic and chromatographic techniques, as listed in Table 9. 

A brief mention of the several modes of capillary electrophoresis was made above, will now briefly describe each of these modes. 

Capillary zone electrophresis (CZE), one of the separation modes of capillary electrophoresis (CE), is a powerful separation technique for many ionic substances. CZE has a high resolution for ionic species but not for non-ionic species. For the separation of nonionic species, micellar electrokinetic current chromatography (MECC) can be applied. These CE methods are attractive tools for the determination of pyridine coenzymes because of their high separation efficiency, easy operation, and low running costs. 

The principles of the various modes of capillary electrophoresis are examined, and applications of these techniques in the molecular weight characterisation of polymers are discussed. 40 refs. 

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