Continuous flow isoelectric focusing

The development of electrophoretic techniques afforded possibilities for fractionations based on charge density differences. Duxbury (1989) has reviewed applications of different electrophoretic separation methods, including zone electrophoresis, moving boundary electrophoresis, isotachophoresis, and isoelectric focusing (IEF). Preparative column electrophoresis (Clapp, 1957) and continuous flow paper electrophoresis (Hayes, 1960 summarized by Hayes et al., 1985) methods have been used to separate components isolated from sapric histosol soils. These techniques allowed separation of polysaccharides from the colored components the electrophoretograms of the colored components were diffuse, showing a continuum of components of different charge densities. 

While some techniques require the absence of electroosmotic flow during the separation itself (capillary gel electrophoresis and capillary isoelectric focusing), most common techniques exploit electroosmotic flow for sample introduction and detection. Electrophoresis in buffer-filled capillaries uses electroosmotic flow in an analogous manner to a chromatographic mobile phase the flow is used to transport analyte from cathode to anode and separation occurs continuously between introduction and detection. 

Many novel electrophoretic devices and techniques have been proposed for continuous electrophoretic separations such as the velocity-stabilized Biostream/Harwell device (9-11), the recycle continuous-flow electrophoresis device (12-14), Bier s isoelectric focusing technique (15),... 

Fig. 6.31. Schematic arrangement of an apparatus for continuous flow isoelectric focusing, a. Electrode compartment b, semi-permeable membrane c, running space.

The experimental implementation of this technique has been demonstrated by the fractionation of various samples of silica particles by applying natural gravitation and a counteracting cross-flow gradient. The silica particles were separated according to size. Isopycnic or isoelectric focusing FFF, already performed on an analytical scale, can easily be transformed into such continuous large-scale separation. 

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