Studies On Negative Pressure Sampling And Sample Stacking On A Microfluidic Chip

Chip-based capillary electrophoresis (chip-based CE) has emerged as a main area of development in the field of microtatal analysis systems (μTAS). Currently, particular interests are focused on achieving high speed, non-biased sampling and on-line sample preconcentration to meet the requirements for analysis of real world samples. The present work proposed negative pressure sample injection method for chip-based CE for the first time and find its application in on-line sample stacking and high-throughput analysis.In Chapter 1, sample introduction and on-line sample electrokinetic stacking techniques for chip-based capillary electrophoresis are reviewed, including electrokinetic sampling method, pressure sampling method, field-amplified sample stacking, Isotachophoresis (ITP) and Sweeping.In Chapter 2, a simple method for injecting well-defined non-biased sample plugs into the separation channel of a chip-based CE system was developed by a combination of flows generated by negative pressure, electrokinetic and hydrostatic forces. This was achieved by using only a single syringe pump and a single voltage supply at constant voltage. The liquid levels of the four reservoirs were optimized to prevent sample leakage during the separation stage. The approach considerably simplified the operations and equipment for pinched injection in chip-based CE, and improved the throughput. Migration time precisions of 3.3 and 1.5% RSD for rhodaminel23 (Rhl23) and fluorescein sodium (Flu) in the separation of a mixture of Flu and Rhl23 were obtained for 56 consecutive determinations. The negative pressure pinched sample injection approach for chip-based CE presented here proved to be a more efficient, alternative to electrokinetic pinched sample method.In Chapter 3, a novel method for injecting volume-based sample plugs into the separation channel used for on-chip sample stacking in a chip-based CE system was presented. A six-channel microchip was developed that allows the formation of volumetrically defined sample plugs in 5 s for sample stacking by negative pressure sampling technique. This approach considerably simplified the operations and the equipment for large volume sample injection in chip-based sample stacking.Compared with the non-stacking method, the peak height of FTTC-labeled Valine (Val) and Alanine (Ala) increased 63- and 103-fold respectively. By selecting proper buffer and sample matrices, it is anticipated that this method for sample on-chip concentration is also applicable to ITP and Sweeping techniques.In chapter 4, we simplified the original negative pressure sampling device by substituting micro-vacuum air pump and electromagnetic gas valve for syringe pump and three-way valve driven by step motor respectively. Compared with the original device, the simplified one can be operated without the control of a computer and with more friendly operation, higher negative pressure efficiency, further more, the total cost of the simplified one is only one tenth of the original one. High-throughput electrophoretical separations on microchip was realized by using the simplified negative pressure sampling device and combining with microsample vials array. The highest sampling throughput of 1200 h"1 was obtained by using injection times of 0.5, 1.5 s for electrophoretical separation, and Is for sampling changing respectively, with a sample consumption of only 0.1 fih for each cycle.In chapter 5, a 3-layer glass eight-channel chip was fabricated for the first time to further test the performance of the simplified negative pressure sampling device. Bias-free sample plugs can be injected into channels within 1 s by the simplified sampling device, and the high voltage supply system for multi-channel separation was simplified by a single voltage supply at constant voltage.