Separation of binary solution by liquid-liquid microextraction on EWOD digital microfluidics

This paper reports the separation of a binary solution using liquid-liquid microextraction enabled by an electrowetting on dielectric (EWOD) digital microfluidics. Liquid-liquid extraction (LLE) is a method to separate compounds based on their relative solubilities in two different immiscible liquids. By EWOD DMF operation, droplets of an aqueous binary solution and ionic liquid which is immiscible with water were created and controlled to perform multiple cycles of LLE in series. It was resulted that each compound in the binary solution was separated and concentrated into each immiscible liquid phases. Moreover, EWOD DMF operation split the merged droplet of water and ionic liquid into two droplets of each phase so that complete phase separation was achieved. Spectrophotometry function was miniaturized and integrated into the platform for real-time concentration measurement. After two cycles of serial LLE, molecules of green organic dye were successfully removed from the binary solution droplet (~ 100 nL) and left the droplet concentrated with yellow dye molecules.