Dispersion sources for compact geometries on microchips

Folding the separation channel in a microchip device generally introduces an additional geometrical contribution to analyte dispersion through lateral variations in both migration distance and field strength. The geometrical dispersion generated depends on the ratio of the analyte transverse diffusion time to the time that the analyte band spends traversing the turn. A one-dimensional model has been developed which predicts the amount of excess dispersion introduced by turns in microchip channels. This model accounts for migration length differences, field strength differences, and transverse diffusion effects and accurately describes the experimental data. The introduction of turns into the channel on a microchip is shown to reduce separation efficiency compared to the same separation length in a straight channel, especially for molecules with small diffusion coefficients. Several methods to reduce geometrical dispersion are examined including the manipulation of channel width and analyte velocity and the use of complementary pairs of turns.