A microfluidic device comprising a hydrophilic microchannel structure in which there is a functional unit that comprises a microconduit which a) is intended for the transportation of liquid aliquots, and b) has an inlet end and an outlet end between which there is a capillary valve I, which preferably is based on the presence of a local non-wettable surface area. Microconduit I further comprises one or more additional capillary valves, typically one. At least one of the additional valves is upstream of capillary valve I, such as at the inlet end of the microconduit.