Spatially-resolved fluorescence spectroscopic study on liquid/liquid extraction processes in polymer microchannels

The liquid/liquid extraction of an Al3+-DHAB chelate (DHAB = 2,2'-dihydroxyazobenzen) from water to 1-buthanol (BuOH) in a polymer-based microchannel chip was studied by spatially-resolved fluorescence microspectroscopy. A microchannel (depth, 10 mu m; width, 200 mu m) was fabricated on a styrol-plastic substrate by an imprinting method. A template for imprinting was prepared by photolithography, in which a spatial pattern printed on a transparency film by a standard drawing software package was used as a photomask. When two immiscible fluids were brought together into the channel chip by pressure-driven flow at the same velocity, a stable parallel stream was observed for each phase without mutual mixing. The extraction of Al-DHAB from water to BuOH was then studied as a fluorescence-intensity profile of the complex in the BuOH phase along the flow direction as well as along the channel-width direction. It was confirmed that extraction proceeded with solution flow and was governed by the contact time between the two phases. The results were explained by a one-dimensional mass-transfer model along the channel-width direction.