Electroosmotic pumping is highly efficient in capillaries of less than 100 mu m inner diameter bearing an immobilized surface charge. Electric fields in the kV cm-1 range allow for liquid motion of several mm s-1 in the case of an aqueous electrolyte. This pumping mechanism is used for miniaturized chemical analysis systems. Flow and mixing behaviour in branched channels are characterized. A capillary electrophoresis device allows for repetitive, electroosmotic injections of 100 pL samples, for efficiencies of up to 200000 theoretical plates in less than a minute, and for external laser induced fluorescence detection at any capillary length of choice between 5 and 50 mm.

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SummaryMiniaturization of separation columns implies equally reduced volumes of injectors, detectors, and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron-sized structures such as channels. This is demonstrated by two examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical path length cell despite its volume of 1 nL. A capillary electrophoresis device allows integrated injections of 100 pL samples, efficiencies of 70,000 to 160,000 theoretical plates in 10 to 20 seconds, and external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm.

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A novel concept for repeated column switching in capillary electrophoresis is presented. Theoretical considerations predict high plate numbers per volt. Using micromachining techniques, a planar glass structure has been fabricated, which contains four capillaries of 20 mm length arranged in a square. Laser fluorescence detection gave a cycle time of 70 s for 2.5 kV applied. After five cycles a theoretical plate number of 40,000 was reached.