Microchip devices for high-efficiency separations

We have fabricated a 25-cm-long spiral-shaped separation channel on a glass microchip with a footprint of only 5 cm x 5 cm. Electrophoretic separation efficiencies for dichlorofluoroscein (DCF) on this chip exceeded 1 000 000 theoretical plates and were achieved in under 46 s at a detection point 22.2 cm from the injection cross. The number of theoretical plates increased linearly with the applied voltage, and at a separation field strength of 1170 V/cm, the rate of plate generation was similar to 21 000 plates/s. The large radii of curvature of the turns minimized the analyte dispersion introduced by the channel geometry as evidenced by the fact that the effective diffusion coefficient of DCF was within a few percent of that measured on a microchip with a straight separation channel over a wide range of electric field strengths. A micellar electrokinetic chromatography separation of 19 tetramethylrhodamine-labeled amino acids was accomplished in 165 s with an average plate number of 280 000. The minimum resolution between adjacent peaks for this separation was 1.2.