Studies On Microfluidic Chip-Based Liquid-Liquid Extraction And Multiphase Laminar Flow Separation Techniques

Microfluidic chip-based liquid-liquid extraction and multiphase laminar flow separation have proved to be effective means to perform on-chip sample pretreatment. In this work, several microfluidic chip-based systems were developed to perform liquid-liquid extraction and multiphase laminar flow separation.In the first chapter, the developments of the solvent microextraction, microfluidic chip-based liquid-liquid extraction and multiphase laminar flow separation were reviewed. More than 80 papers published in these fields were cited.In the second chapter, an approach for microfluidic liquid-liquid extraction at the subnanoliter-scale was developed for on-chip sample pretreatment. Organic solvent droplets of a few hundred pLs were trapped within micro recesses fabricated in the channel walls of a microfabricated glass chip. The extraction was performed by delivering aqueous samples through the channel, with the sample stream continuously flowing adjacent to the droplet. The analytes in aqueous streams were enriched within the droplet with high enrichment factors owing to both phase transfer and dissolution of organic solvent into the bypassing aqueous sample. The system proved to be an efficient means for achieving high enrichment factor of over 1000 with sample consumption of only a few μLs. An aqueous butyl rhodamine B (BRB) solution was used as sample to demonstrate the performance of the present system.In the third chapter, a novel miniaturized liquid-liquid extraction system under stopped-flow manipulation mode was developed by stopping the organic solvent flow in the extraction channel while the aqueous phase flows by continuously in another merging channel. The analyte in aqueous flow was transferred into the stationary organic phase in the microchannel through molecular diffusion between the two phases. Focusing of analyte in the organic phase near the interface of aqueous and organic phases and concentration gradient of analyte along the organic phase microchannel, owing to dissolution of organic solvent into the flowing aqueousstream, was observed for the first time. The analyte was focused near the interface because of the solute from the sample solution into the extractant and dissolution of the extractant into the sample solution. The effects of both phase transfer and dissolution of organic solvent were investigated. The focusing effect of the analyte in organic phase could be adjusted by changing the dissolution rate of the organic solvent into the aqueous sample flow. The present extraction chip system was applied in the determination of Al3+ using Al3+-DHAB-isobutanol extraction system.In the fourth chapter, a microfiuidic chip based on multiphase laminar flow separation coupled to ion selective electrode detection was developed. The system was applied for the determination of potassium in serum. Potassium ions were separated from the serum matrix by employing the chip-based multiphase laminar flow separation system. Both sample and acceptor streams were driven by gravity. Potassium ions in the acceptor stream were determined by using an ion selective electrode integrated on the chip.