a microfluidic system has an electroosmotic flow pumping means for propelling fluids through a series of microchannels and selection valves . pump channels are configured in groups which may be fabricated singly or in multiple groups onto a substrate . a tube filled with an immobilized polymer provides a means to apply voltages across pump channels , while prevents passages of fluids through it . it also avoids electrolysis and bubble formation in or close to the microfluidic channels . the selection valves provide for routing functions within the microfluidic system and can also be configured to route fluids outside the system . a rate monitoring system is provided for determining and compensating for flow rates . in one application the microfluidic system may be configured to operate as a small volume pipettor or other fluid transport or analysis device . a micro - dialysis jacket is additionally provided to permit desalting , ph adjustment , concentration adjustment , and other functions .