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In recent years a number of new separation techniques employing high voltages and narrow bore capillaries have been brought to light.
These include:
The first two techniques in the above list can be viewed as high tech instrumental analogues of the well know slab-gel electrophoresis, whereas MECC makes use of a form of chromatographic partition to achieve the separation of the components. However, the capillary electro- technique which most closely resembles modern HPLC is electrochromatography.
- Capillary Electrophoresis (CE or CZE)
- Capillary Gel Electrophoresis (CGE)
- Micellar Electrokinetic Capillary Chromatography (MECC)
Introduction
In conventional liquid chromatography the flow of eluent is generated by the application of a pressure gradient, which is usually provided by means of a high pressure mechanical pump. However, under certain conditions, the mobile phase can be forced to migrate through the chromatographic medium by the application of an electric field.This phenomenon of electrically induced fluid flow is commonly referred to as electro-osmosis or electro-osmotic flow. Liquid chromatography making use of this effect, where the pump is substituted by a high voltage power supply, has come to be know as electrochromatography.
Electro-osmotic flow, is a familiar concept to anyone with experience of capillary electrophoresis in any of its various forms. This phenomenon, however, is not restricted to open capillaries, such those used in conventional CE, micellar CE etc., but may also occur in tubes packed with small particles of silica gel, either as unmodified silica or chemically derivatised reversed phase materials.
J.H. Knox and I.H. Grant, Chromatographia 32 (1991) p317.
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