| Recently, microfluidic analytical systems aiming at miniaturization, integration, portability of analytical instruments have been growing rapidly. The integration of sample pretreatment into microfluidic devices represents important significance towards achieving true miniaturized total analysis systems. Since sample pre-treatment usually involves between-phase mass transfer and phase separation, it is rather difficult for the sample pretreatment units to be integrated on microfluidic devices. Thus, compared to the research achievements on microchips for capillary electrophoresis, the research work on microfluidic chips with integrated sample pretreatment units are relatively less developed.Liquid-liquid extraction is an important sample pretreatment technique that serves the function of both pre-concentration and pre-separation. It has the merits of good selectivity and high enrichment factors. The present work is aimed to establish some basic microfluidic liquid-liquid extraction systems, and to investigate the possibility of coupling on-chip liquid-liquid extraction (LLE) unit to chip-based capillary electrophoresis (CCE) system. The thesis is divided into four parts.In chapter 1, the historical development of liquid-liquid extraction and the recent advance of chip-based liquid-liquid extraction systems were reviewed.In chapter 2, a novel micro flow injection wetting film liquid-liquid extraction system on polymer-based microfluidic chip was established. Wetting film liquid-liquid extraction is based on the fact that a uniform organic solvent thin film can be coated on the inner wall of polymeric tubing when a segment of water-immiscible organic solvent is driven to pass the tubing. The hydrophobic species in aqueous sample solution may be extracted into the film when the sample solution is driven through the tubing, and the extracted species can be eluted with asuitable eluent and on-line detected. In this chapter, polycarbonate (PC) sheet was used to fabricate the microfluidic chip with hydrophobic channel. A straight channel was hot imprinted onto a PC sheet by using a metal wire as a die. Hydrostatic pressure generated by a fused-silica capillary connected to the end of the channel was employed to drive fluids, and a vials array was employed to dispense sample solution and solvent. Butanol was used as both coating solvent and eluent, butyl-rhodamine B (BRB) was used as model analyte. When butanol, aqueous sample solution and butanol bands were sequentially driven by the hydrostatic pressure to passed the channel, the film coating, extraction and elution were consequently operated. Fluorescence signal of the analyte was on-channel detected with a LIF detector. It was observed that non-constant flow-rate was generated with the gravity pump for the two-phase segmented flow. However, this does not deteriorate the reproducibility of the analytical signals produced by the micro flow injection wetting film extraction system, provided that regular sample and solvent aspiration was conducted. The influences of various experimental parameters, such as coating solvents, time duration of coating, velocity of flow, length of channel, acidity of the sample medium and sampling volume, were investigated. Under optimized conditions, a concentration factor of 24-fold was achieved by the developed system at the sample consumption of 4 μL. The LOD for BRB was 6.00xl0"9 mol/L, and the sample throughput rate was 19 h"1. The developed system was used to determination of rhodamine B in dye contaminated dry shrimps, and satisfactory recoveries were obtained.In chapter 3, a microfluidic, micro-porous membrane liquid-liquid extraction system was developed. In micro-porous membrane liquid-liquid extraction system, a porous polymer membrane is used to separate the aqueous sample flow in a donor channel and organic solvent flow in an acceptor channel, and extraction occurs in the boundary of the solvent-wetted membrane and the aqueous sample solution. In this chapter, the microfluoidic extraction chip was designed to be composed of two pieces of channel-etched glass substrates and a piece of porous PTFE membrane. The donor channel on bottom glass substrate and the acceptor channel on the top substrate were separated by the PTFE porous membrane that was sandwiched between the two glasssubstrates, the size of the membrane being smaller than that of the glass plates but big enough to cover the channels. As high-temperature thermal bonding technique did not work for the 3-layer structure made of different materials, a novel epoxy-glue sealing technique was developed. The "glass-polymer-glass" sandwich was aligned and clamped. Epoxy glue was applied to the edges of the clamped assemble. The liquid epoxy spread into the fine gap between the two glass substrates, due to the surface tension, until it reached the edges of the polymer membrane. After the glue was solidified (60°C for 3 h), the 3-layer chip was sealed. In the present extraction system, hydrostatic pressure was employed to drive fluids, and BRB and butanol were respectively used as model analyte and extraction solvent. Influences of various experimental conditions, such as flow rates, pore size of the membrane and width of the channels were investigated. Under optimized conditions, an enrichment factor of ca. 3 was achieved at the sample consumption of ca 140 (xL. The sample throughput rate was 15 h'1, and the between-run carry-over was less than 2.5 %. The developed porous-membrane-based microfluidic liquid-liquid extraction system provided a technical support for integration of micro liquid-liquid extraction device for sample pretreatment onto microfluidic analytical chips.In chapter 4, an integrated multi-layer microfluidic chip for supported liquid membrane extraction-back-extraction coupled with chip-based capillary electrophoresis separation (SLMEBE-CCE) was fabricated, and its analytical performance was demonstrated. In SLMEBE, the hydrophobic analyte is extracted from aqueous solution into the supported liquid membrane (organic solvent) first, and then back extracted into aqueous acceptor phase. Due to the back-extraction, the concentrate is, rather than organic medium, an aqueous solution that matched to the aqueous running buffer of capillary electrophoresis. Therefore, direct coupling the extraction to CE is possible. In this chapter, a multi-layer chip was designed to be composed three glass substrates and polymer membrane. The CCE unit was designed to be located in the up part while the SLMEBE underneath the CCE unit. The top and middle glass substrates were used to construct a CCE unit, and they were thermal bonded. As the acceptor channel for the SLMEBE was etched on the back surface ofthe middle glass substrate, the middle glass substrate was shared by both the up CCE unit and the underneath SLMEBE unit. Thus, the middle glass substrate that already bonded to the top glass substrate, the bottom glass substrate with an acceptor channel, and a porous PTFE membrane were sealed to form a sandwich-like extraction-back-extraction unit by using the novel sealing method invented in the Chapter 2. Gravity driven was used for SLMEBE and EOF for CCE, and the two units were interfaced with a flow-split flow-through-cell, which was a 0.35 mm i.d vertical hole drilled through the top and middle glass substrates and connecting the sample injection channel in CCE unit and acceptor channel in the SMLEBE unit. Using fluorescein as model analyte and BRB as model interferant, the analytical performance of the on-chip coupled SLMEBE-CCE system was examined. Compared to the signals observed with CCE without SLMEBE pretreatment, the signal of the fluorescein observed by the coupled SLMEBE-CCE system was enhanced by a factor of 7, and the ratio of fluorescein-to-BRB signals was increased by a factor of 30, demonstrating the potential of the coupled system for analyzing samples with complicated matrix.The main novelty of the present work is summarized as:1. Developed a polymer-chip-based, gravity-driven micro flow injection wetting film liquid-liquid extraction system.2. Invented a simple and useful sealing method for glass-polymer-glass multi-layer chips. With this method, a novel micro-porous membrane liquid-liquid extraction chip was developed to concentrate and on-line detection of fluorescence compound.3. Established a coupled supported liquid membrane extraction-back-extraction and capillary electrophoresis separation system on an integrated multi-layer microfluidic chip by the application of the proposed step-wise bonding and sealing technology.
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