Circulation microchannel for liquid-liquid microextraction

A new method has been developed for liquid-liquid microextraction utilizing a circulation microchannel. A glass microchemical chip having a circular shallow microchannel in contact with a surrounding deeper microchannel was fabricated by a two-step photolithographic wet-etching technique. Surface modification reagent was selectively introduced to the shallow channel by utilizing capillary force, and the surface of the shallow channel was selectively made hydrophobic. With the aid of the hydrophobic/hydrophilic surface patterning, it was possible to keep organic solvent in the circular channel while the aqueous sample solution was continuously flowing in the deep channel. As a result, concentration extraction from sample solution to stationary extractant with a nanoliter scale volume became possible. Concentration extraction has been difficult in a multiphase continuous flow. Function of the newly developed microextraction system was verified with methyl red as a test sample, and concentration extraction to reach equilibrium was successfully carried out. A novel surface modification method utilizing frozen liquid as a masking material was also developed as a reverse process to make the shallow channel hydrophilic and the deep channel hydrophobic. Visualization of circulation motion inside the circular shallow channel induced by flow in the deep channel was observed with a particle tracing method.