DISPERSION SOURCES FOR COMPACT GEOMETRIES ON MICROCHIPS

Folding the separation channel in a microchip device generally introdu ces an additional geometrical contribution to analyte dispersion throu gh lateral variations in both migration distance and held strength. Th e geometrical dispersion generated depends on the ratio of the analyte transverse diffusion time to the time that the analyte band spends tr aversing the turn. A one-dimensional model has been developed which pr edicts the amount of excess dispersion introduced by turns in microchi p channels. This model accounts for migration length differences, fiel d strength differences, and transverse diffusion effects and accuratel y describes the experimental data. The introduction of turns into the channel on a microchip is shown to reduce separation efficiency compar ed to the same separation length in a straight channel, especially for molecules with small diffusion coefficients. Several methods to reduc e geometrical dispersion are examined including the manipulation of ch annel width and analyte velocity and the use of complementary pairs of turns.