Quantitative extraction using flowing nano-liter droplet in microfluidic system

Quickly extraction system using dispersed droplet in T-shaped microchannel has been constructed and investigated for the determination of aluminum in water. The droplet was generated in T-shaped microchannel with 600 μm wide and 200 μm deep in continuous phase and 70 μm wide and 20 μm deep in dispersed phase by flowing two immiscible solutions, buffer solution containing aluminum and tributyl phosphate as dispersed phase. By varying the flow rate of two solutions, the droplet volume could be controlled in the range from 0.6 to 32 nL. Using this droplet generation in microchannel, aluminum in continuous phase was extracted with 2,2-dihydroxyazobenzene as a metal chelate from buffer solution to tributyl phosphate for 1 s, which was 90 times shorter than that of a conventional extraction method using a separatory funnel. Estimated overall mass transfer coefficient was to be 57 × 10−4 mm s−1 with 0.6 nL droplet. And quantitative extraction was performed in this extraction system by detecting droplets before it reached to extraction equilibrium. Furthermore, this extraction system was applied to environmental analysis for evaluation of its validity, and the results were in agreement with the conventional extraction method (r = 0.92).