Studies On Microfluidic Analysis Systems Based On Liquid Phase Mass Transfer

In recent years, the fast development of micro total analysis systems (μ-TAS) indicates it as one of the most up-to-date technology in the world. As the core technology ofμ-TAS field, microfluidic chips have micron-scale inner diameter (at least one dimension) channels which increase the fluids specific interfacial area while decrease the molecular diffusion distance, both effects are quite advantageous for effective liquid phase mass transfer. Separation, extraction and reaction in micro-chip are usually more efficient than those in conventional macro-vessels. The present work is aimed to establish some simple, cheap microfluidic analysis systems based on liquid phase mass transfer. The focuses are both on enhancing the mass transfer amount and on using simple, cheap detectors after mass transfer. The thesis is divided into four parts.In chapter 1, the development and present level of microfluidic analysis systems based on liquid phase mass transfer was reviewd. The classification by solution solubility was generalized while both non-membrane liquid-liquid extraction chips and non-membrane multiphase laminar flow separation chips were particularized.In chapter 2, a microfluidic chip-based sequential injection system with trapped droplet liquid-liquid extraction preconcentration and chemiluminescence detection was developed for achieving high sensitivity with low reagent and sample consumption. The microfabricated glass lab-chip had a 35-mm-long extraction channel, with 134 shrunken opening rectangular recesses (L100×W50×D25μm) arrayed within a 1-mm length on both sides of the middle section of the channel. A 20-mm-long silica capillary with one end connected to the channel was inserted into a sample or reagent vial, and used as a sampling probe. Gravity driven hydrostatic flow was used for sequential delivery of sample and reagent solutions. Ketonic peroxyoxalate ester solution was filled in the recesses forming organic droplets, and keeping the aqueous sample solution flowing continuously in the extraction channel; analytes were transferred from the aqueous phase into the droplets through molecular diffusion. After liquid-liquid extraction preconcentration, catalyst and hydrogen peroxide solutions were introduced into the channel, and mixed with analytes and peroxyoxalate ester to emit chemiluminescence light. Optimization studies were conducted on recess dimensions, organic solvent and other parameters for extraction and reaction. The performance of the system was tested using butyl rhodamine B, yielding a precision rate of 4% RSD (n=5) and a detection limit of 10^-9 M. Within a 17 min analytical cycle, the consumption of sample and peroxyoxalate solutions were 2.7μL and 160 nL respectively.In chapter 3, the microfluidic chip based sequential injection system with trapped droplet extraction and chemiluminescence detection in chapter 2 was further exploited for trace aluminium analysis. In the system, an integrative probe on the monolithic microchip was used for sample introduction while a series of recesses arrayed at both sides of the microchannel were used for organic droplet trapping liquid-liquid extraction. The system is permanently organic solvent durable. Within a 12 min analytical cycle, the consumption of sample and peroxyoxalate solutions was 1.8μL and 120nL respectively, yielding an 85 times enrichment of aluminium dihydroxyazobenzene complex, a precision rate of 4.5% (RSD, n=6) and a detection limit of 1.6×10^-6mol/L, respectively.In chapter 4, mechanical carving with precise numerical control was applied to fabricate the 500μm-deep channel on polycarbonate microfluidic chip, in order to increase mass transfer amount and improve the absorbance detection sensitivity. A simple 2-dimension photometric detection system using a cheap charge coupled device (CCD) without need for other optical device was developed to achieve colorimetric measurement in the microfluidic chip-based multi-phase laminar-flow system. Compared with most of the chips fabricated by reported methods, the present system has the advantages of simple configuration and ease of fabricating, and ten folds of optical path enhancement was achieved. The system performance was tested by the chromogenic reaction of Fe³⁺ and KSCN, achieving a precision of 0.6% (RSD, n=15) and a detection limit of 5mg/L. The single sample analysis time is less than one minute.