Optimum kinetic performance of open-tubular separations in microfluidic devices

A survey is made of the different factors contributing to the kinetic performance of open-tubular separation channels. Being representative for most of the channels used in microfluidic devices, the main focus is on channels with a rectangular format. Kinetic plots of t(0)/N-2 versus N are established to allow for a visual selection of the ideal channel format and dimensions. These plots for example show that in the pressure-driven mode a channel with a flat-rectangular crosssection (top and bottom wall covered by a retentive layer) can always yield slightly faster (some 15%) separations than a cylindrical capillary, provided the channel depth is optimized. If the channel depth is fixed, the optimal w/d-ratio depends on the required plate number. In electrically driven flows, the situation is reversed and rectangular channels with a small width are to be preferred, and the cylindrical capillary format becomes the best format.