Abstract

Open tubular separations in the liquid phase including capillary electrophoresis are conventionally practiced in capillary tubes with diameters of tens of micrometers and lengths of tens of centimeters. Structures having similar dimensions can be fabricated on planar substrates using micromachining techniques. Microfabricated separation devices have been demonstrated for capillary electrophoresis,^{1 2} synchronized cyclic electrophoresis,3 and free-flow electrophoresis.4 The separation performance hinges upon minimizing the spatial extent of the injection plug and detector observation region, and optimizing the separation field strength. The injection plug width can be minimized by fabricating narrow channel dimensions for the injection valve, and the detector observation region can be minimized by having a small excitation volume or tight spatial filtering for fluorescence detection. For high speed separations, the separation column does not have to be long, e.g., < 1 mm long. Unfortunately, the footprint of these microfluidic devices is usually > 200 mm2, but the channel manifold can be designed such that the potential drop is small in areas not contributing to the separation. This results in a maximum field strength in the separation column. Because the resistance in the channel is proportional to the length and inversely proportional to the cross-sectional area, thin channels are fabricated for the injection valve and separation column, and wide channels for all other sections of the channel manifold.

© 1998 Optical Society of America