| Microchip based capillary electrophoresis (MCE) exhibits the advantages of extremely low consumption of reagents/samples and fast analysis speed, but the relative high fabrication cost of glass or fused silica chips limits its wide application in the real analysis. Polymer microchips can be easily made and are much cheaper, have been widely used instead of glass and fused silica chips. However, most of plastics are hydrophobic and can unspecifically adsorb biomacromolecules, which cause surface contamination and alter the electroosmotic flow, degrade the separation efficiency and repeatability. Also, due to the relative short separation channel of microchips, tiny difference of liquid levels or surface curvature in different reservoirs may cause unexpected pressurized flow, negatively affect the separation efficiency and the repeatability.Therefore, this dissertation focuses on the research of approaches to eliminate the non-specific adsorption of analytes or sample matrices, and improve the separation efficiency and reproducibility. Originalities include:(1) Hydroxypropyl cellulose (HPC) was used as buffer additive to establish a method for rapid separation and detection of glyphosate and glufosinate residues in agricultural products.(2) Polyacrylic acid was used as a multifunctional additive in COC microchip electrophoresis for the separation of rhodamine B (RhB) and rhodamine6G (Rh6G). The method was used for the detection of these two compounds in rea food samples.(3) A mixed solution of acetone and cyclohexane as a solvent for channel restoration, defective channels were successfully repaired.(4) By implementation of an extra sample waste reservoir and an extra buffer waste reservoir on the cross chip, a design for effective pinched injection was proposed and the performance of the chip electrophoresis was improved.The thesis contains five chapters:Chapter1:Microfluidics was shortly reviewed, manily on the fabrication process of the microchips, injection methods for microchip electrophoresis, surface modification of microfluidic channels and the applications of microchip electrophoresis in real analysis.Chapter2:A microchip electrophoresis system with laser induced fluorescence (LIF) detection for rapid and sensitive analysis of glyphosate (GLYP) and glufosinate (GLUF) residues was described. Systematic optimization of experimental conditions was performed to achieve highly efficient analysis. Under the selected condition, GLYP and GLUF were efficiently resolved from sample matrices with a buffer containing10mmol/L borax and2.0%(m/v) hydroxypropyl cellulose at pH9.0. The number of theoretical plates of1.0×106/m was attained for both analytes. Derivatization at lower concentrations (＜10μg/L) was also examined, successful detection of0.34μg/L GLYP and0.18μg/L GLUF was confirmed. The system was applied for the determination of both analytes in real samples without any preconcentration involved. Recoveries of GLYP and GLUF spiked in these samples were84.0-101.0%and90.0-103.0%, respectively.Chapter3:This chapter describes the utilization of polyacrylic acid as multifunctional buffer additive for dynamic modification of COC to reduce adsorption of rhodamine dyes onto the microchannel, and suppress the effect of pressurized flow for the separation efficieny through increase of the buffer viscosity. Rhodamine B (RhB) and Rhodamine6G (Rh6G) were well resolved. The parameters were systematically investigated and by using20mmol/L phosphate buffer with0.36%polyacrylic acid in70%methanol at pH5.0, the number of theoretical plates of7.0×105/m was achieved. Under the selected condition, the relative standard deviations of RhB and Rh6G detection (n=5) were not more than0.72%for migration time, and not more than2.6%for peak area, respectively. Limits of detection (S/N=3) were0.17and0.34μg/L repectively. RITC-labeled amino acids were well resolved with the selected system too. It was also found that polyacrylic acid might significantly affect the observed electroosmotic flow, and it was even reversed at higher polyacrylic acid concentrations. The method was applied for the determination both RhB and Rh6G in ham, tomato sauce, chili and satisfactory standard addition recoveries of84.6-106.7%were attained.Chapter4:Remedy and surface recovery of COC microchannels were realized through rinsing with a solvent mixture that with proper solubility of COC. In this work, the effectiveness of rinsing of microchannel with a8:2(v/v) mixture of acetone and cyclohexane for recovering the microchips with poor performance was examined. The results indicated that the method could recover the mcirochips with non-uniform surface status, improperly sealed microchannels and contaminated microcahnnels by proteins. Atomic force microscopic measurement showed that the solvent rinsing could reduce the roughness of the microchannel surfaces. Efficient separation of several FITC labeled amino acids was achieved on microchips remedied by the proposed method. But the clogged microchannels could not be remedied by this method. Meanwhile, the experiments also showed that for microchip with good performance, treatment with the solvent mixture had no adverse effects.Chapter5:A novel chip structure is used, with an extra sample waste reservoir and an extra buffer waste reservoir. Proper level differences between sample reservoir and the extra sample waste reservoir, buffer waste reservoir and the extra buffer waste reservoir were maintained. The electrodes were placed in the extra sample and buffer waste reservoirs. In the sample injection stage, because of the continuous flow in the channel between the sample reservoir and the extra sample waste reservoir, the retreated sample was conducted into the extra sample waste reservoir, preventing the dilution of the sample by the retreated buffer and improving the reproducibility. By optimizing the sample injection time, it may be possible to ensure analytes entering the separation channel while removing the slower migrating sample matrices and other components. The use of extra buffer waster reservoir may avoid the waste sample of the previous separation entering the separation channel and leading to baseline elevation, which is also benefical to the reproducibility. Experimental results showed that FITC labeled organophosphorus herbicides could be repeatedly analyzed more than120times on the proposed microchips. |
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