Studies On Microfluidic Capillary Electrophoresis System With UV Absorbance Detection

Microfluidic systems have become more and more important in the field of analytical chemistry. Various detection methods on these microsystems are essential for the identification and quantification of chemical species that are being analyzed. UV/Vis absorbance detection has widely applied in CE and HPLC systems. However, its application in microfabricated chips has been limited owing to the short optical path-length in planar chip structures. Efforts have been made to overcome such limitations, with some success, but resulting in rather sophisticated structures. In this dissertation, a miniaturized capillary electrophoresis system with slotted micro-vial array based sample introduction system and UV detection was developed and applied in fast separation of sulphamethoxazole (SMZ) and trimethoprim (TMP) in sulphatrim tablets. In addition to the previous work, a UV absorbance detection system with sheath flow configuration for glass CE chip was also developed for the first time.In the first chapter, the development of UV/Vis absorbance detection system on microfluidic chips and its applications were reviewed. The difficulties of realizing a robust UV/Vis absorbance detection system are discussed.In the second chapter, the development of microfluidic H-channel system for rapid CE separations was reviewed. Applications of the system, coupling to flow-injection and/or sequential-injection sample introduction, for the determination of FITC- labeled amino acids by laser-induced fluorescence or LED-induced fluorescence with liquid core waveguide detection , trace metals by chemi-luminescence, carbohydrates by amperometry, and drugs by UV absorbance are exemplified to illustrate the performance and versatility of the microfluidic system.In the third chapter, a high throughput sample introduction system based on slotted micro-vial array was coupled to a miniaturized capillary electrophoresis(CE) system with short capillary and UV detection to achieve automated and continuous sample introduction and separation in CE system. The sample introduction system is composed of an array of horizontally positioned micro-sample vials with slits fabricated on the bottom of each vial. Sample introduction was performed by linearlymoving the array of vials, allowing the capillary and electrode to sequentially enter the solutions in the vials through the slits achieving sample introduction and separation operation. The present system was applied in fast separation of sulphamethoxazole (SMZ) and trimethoprim (TMP) in sulphatrim tablets, achieving a high throughput of 72 h"1 and a low carryover of 1.4%. Separation efficiency of 11 urn plate height for SMZ was obtained. The detection limits (3a) for SMZ and TMP were 9.8 mg /L and 12.2 mg /L, respectively.In the fourth chapter, a sheath flow configuration flow-cell coupled to two optic fibers was designed to achieve the UV detection on glass CE chip-based system.