Electrophoretic zones systems

Fig.3 A migrating zone of solute molecules (spots) interacting with lipid bilayers (rings) in a chromatographic or electrophoretic separation system. The free solute molecules move (arrows) relative to the liposomes or vesicles in a flow of eluent or in an electric field. The solute molecules may either partition into the membranes and diffuse between the external and internal aqueous compartments of the structures as depicted, or interact with the external surface of the membranes and stay outside.

In Figure 5 we have tried to demonstrate the Influence of both the concentration of fulvic acid and of the aging of the system on the distribution of electrophoretic zones of Fe in diluted seawater. The concentration of 10 mg of FAC in 10% seawater produces a tremendous increase lnj.the cationic zone/tailing of Fe, amounting to 80.7% of the total Fe present (without FAC only 1.2% of Fe is in the cationic tailing zone). However, after aging 27 days, this zone dropped to only 0.4% in favour of the anionic zone (48.4%). At FAC concentrations of 100 mg dm the anionic Fe zone amounted to 9%, and after 27 days it amounted to 79.6% of the total Fe. 

Table VI. Distribution of electrophoretic zones of Fe in 10% seawater-humic acid (HAM) systems (%)...

Figure 1 Layouts of a microfluidic chip combining mixing and reaction zones (capillary system connecting resen/oirs 1-5) with an integrated electrophoretic separation system (reservoirs 6 and 7).

The flow profiles of electrodriven and pressure driven separations are illustrated in Figure 9.2. Electroosmotic flow, since it originates near the capillary walls, is characterized by a flat flow profile. A laminar profile is observed in pressure-driven systems. In pressure-driven flow systems, the highest velocities are reached in the center of the flow channels, while the lowest velocities are attained near the column walls. Since a zone of analyte-distributing events across the flow conduit has different velocities across a laminar profile, band broadening results as the analyte zone is transferred through the conduit. The flat electroosmotic flow profile created in electrodriven separations is a principal advantage of capillary electrophoretic techniques and results in extremely efficient separations. 

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. 

FIGURE 6.12 Schematic view of the CITP separation mechanism. The sample is introduced into the capillary between two electrolyte systems a leading electrolyte (L), having electrophoretic mobility higher than any of the sample components to be separated and a terminating electrolyte (T), having electrophoretic mobility lower than any of the sample components (A). The sample components are separated according to the order of their individual mobility into distinct zones, which are sandwiched between T and L (B). The separated zones move with the same velocity toward the capillary end where they are detected as bands (C). 

The most common classification scheme in electrophoresis focuses on the nature of electrolyte system. Using this scheme, electrophoretic modes are classified as continuous or discontinuous systems. Within these groupings the methods may be further divided on the basis of constancy of the electrolyte if the composition of the background electrolyte is constant as in capillary zone electrophoresis, the result is a kinetic process. If the composition of the electrolyte is not constant, as in isoelectric focusing, the result is a steady-state process. 

Two-dimensional (2D) electrophoretic methods are important variants of electrophoresis. In Section 6.4 we noted that electrophoresis could combine with flow in a 2D system providing continuous (and thus preparative) separation. Fundamentally, this is simply zonal electrophoresis converted into a continuous form by nonselective flow (see Section 7.5). If we observe the separation at different positions along the flow axis (as illustrated for one position in Figure 7.3), we have essentially a series of snapshots of the zones evolving with time. Each component zone is deflected from the flow axis at a unique angle as a consequence of the evolution of the electrophoretic separation. 

Capillary isotachophoresis (CITP) — An electrophoretic separation technique (-> electrophoresis) in a discontinuous -> buffer system, in which the analytes migrate according to their -> electrophoretic mobilities, forming a chain of adjacent zones moving with equal velocity between two solutions, i.e., leading and terminating electrolyte, which bracket the mobility range of the analytes. Ref [i] Riekkola ML, Jonsson jA, Smith RM (2004) Pure Appl Chem 76 443... 

Sample application can be done either by pressure or vacuum, but not electrophoretically as in other capillary electrophoretic systems. The length of the sample plug in experiments performed in the presence of EOF must be carefully determined. Long sample zones may result a focusing step that will not be completed before the moving pH gradient reaches the detection point... 

This chapter introduces the basic concepts and principles of capillary electrophoresis (CE), presenting some background on electrophoresis and capillary electrophesis and describing the components of the system. The two main types of CE, capillary zone and micellar electrokinetic electrophoresis, are described, and a selection strategy, based on the two types of separation, electrophoretic migration and electroosmosis, is presented. 

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