A Microfluidic Liquid-liquid Extraction System Based On Trapped Droplets

As a principal preconcentration and matrix purification technique, liquid-liquid extraction has been used extensively in the chemical and biological analysis. The miniaturization of liquid-liquid extraction device becomes an important issue, particularly in bioanalysis where samples are extremely valuable and reagents are expensive. Microfluidic systems have developed rapidly in miniaturization, automation and integration, which provides a new platform for the miniaturization of liquid-liquid extraction system. In this work, we designed a glass microfluidic chip with a series of micro recesses fabricated in the middle of channels. A simple microfluidic liquid-liquid extraction system based on trapped droplets with high enrichment factors was established, and the extracted analyte could be easily collected.In chapter1, liquid phase microextraction technologies and microfluidic liquid phase microextraction systems were reviewed in general. Microfluidic liquid-liquid extraction systems based on laminar diffusion as well as microfluidic chip-based droplet microextraction techniques were introduced in detail. Finally, the purpose and design of this work were proposed.In chapter2, a microfabricated glass chip was designed and a microfluidic liquid-liquid extraction system based on trapped droplets was established. Photolithographic, wet chemical etching and permanent heat bonding techniques were used for fabricating the glass microfluidic chip. A series of microchambers in the middle of channels were used to capture extractant. An aqueous solution of butyl rhodamine B (BRB) and1-hexanol were used, respectively, as sample and extractant to demonstrate the performance of the system. The capture effect of three microchamber configurations was investigated using a CCD system. Fluorescence intensity of the BRB extracted into the droplets was monitored in situ by a home-built miniaturized laser-induced fluorescence (LIF) system with a532-nm semiconductor laser serving as excitation light source and a photomultiplier as detector. The influences of interface size and aqueous phase velocity on extraction efficiency were investigated. The system achieved an enrichment factor of25, with sample consumption of45μL and extractant consumption of35μL. Finally, collecting method of the extracted analyte was discussed.In chapter3, the microfluidic liquid-liquid extraction system based on trapped droplets was summarized and its prospective application was given.