| Food safety is becoming a critical concern around the world. Traditional separation and detection methods are barely meet the requirements of high sensitivity and rapid analysis speed for on-site food analysis. It is very important to develop analytical methods that are suitable for this purpose. Microfluidic chip electrophoresis, as a miniaturized analytical technique, has been widely used in many fields due to its advantage of rapid separation speed, high separation efficiency, and low sample/reagent consumption. Cyclic olefin copolymer (COC) has been increasingly used for making microchips because of its good optical and mechanical properties. However, its hydrophobicity may cause unspecific adsorption of biomolecules and limit its application in bio-analysis. Modification of COC is thus truly necessary. Based on this fact, this dissertation focuses on the dynamic modification of COC microchips for the chip-based electrophoresis, which include following aspects;(1) A rapid, sensitive analysis method, based on modification of COC microchip channel, was established for the determination of sulfonamides residues of animal origin food. Polyvinyl alcohol (PVA) as the additive was added to the boric acid solution, a network structure of complex was produced between PVA and boric acid, which led to the increase of the viscosity of the buffer solution and the improvement of the separation efficiency. By using this buffer, the baseline separation of four sulfonamides was achieved within1min with the best theoretical plate number up to1.0×106/m. With a simplified sample pretreatment protocol, fast determination of sulfonamides residues in milk and chicken meat was successfully performed using microchip electrophoresis with LIF detection. These results indicate that the proposed method is not only simple, fast and sensitive but also can be successfully used for the determination of sulfonamides at low concentration levels in real food samples.(2) The influence of viscosity on separation was investigated by using the dynamic modification of COC microchip with poly-hydroxyl macromolecules as additives. The separation of three sulfonamides was carried out by using polyvinyl alcohol (PVA)-boric acid buffer and hydroxy propyl cellulose (HPC)-borax buffer and to investigate the viscosity and its effect on the electrophoretic separation.The results showed that the viscosity of PVA-boric acid buffer solution increased with the increase of PVA content, pH and concentration of boric acid, while the viscosity of HPC-borax buffer increased with the increase of concentration of HPC, and decreased with the increase of pH and concentration of borax. Variation of viscosity of both buffers affected the migration time of analytes but had little impact on separation efficiency. In addition, both PVA and HPC are suitable to the separation of fluorescamine labeled amines, such as sulfonamides.(3) The dynamic coating of COC microchip channel was performed with polyethyleneimine (PEI) as modifier in order to make the channel surface bring positive charge to suppress the strong adsorption of rhodamine dyes in the channel. Results of streaming potential indicated that rinsing with10%PEI solution could significantly change the surface charge of the channels. The coated chip could be used for successful electrophoretic separation of rhodamine B and rhodamine6G. Compared with other modifiers, PEI coating could eliminate the adsorption of rhodamines and better separation could be obtained. |
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