ABSTRACT
While most of the progress made in microfluidics in the last decade has, for
very good reasons, been devoted to enhancing the performance of capillary
electrophoresis on a chip, there have been very good reasons to pursue
problems that have been both intellectually and physically orthogonal to the
mainstream. This chapter will discuss issues related to the transport of matter
across flow lines. One strong motivator for this work has been extending the utility of microfluidic processes beyond the clean homogeneous samples
necessary for good chromatographic separations. ‘‘Raw’’ samples, particu-
larly biological fluids, contain a wide range of proteins and larger particles,
most of which are present at concentrations not under experimental control.
This variability in composition, with concomitant variability in fluid con-
ductivity, pH, and concentration of surface-active compounds, renders such
samples incompatible with electrokinetic pumping — the cornerstone of
microfluidic capillary electrophoresis. Such samples, therefore, dictate the
use of pressure-driven flow.
