A Novel Method of Curbing Peak Broadening and Surface Modification by Coating Trace Polyethylene Oxide in Microchip CE

• Main Authors: Shao-Jung Lu, 呂紹榮
• Other Authors: Show-Chuen Chen
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/37822735411396829452

碩士 === 輔仁大學 === 化學系 === 97 === Capillary electrophoresis microchip, μCE, is fast, manageable and low on consumption of samples and reagents. However, the efficiency in real life is less than expected because of the electrodispersion created at the instant of power switch from loading or injection. The incurred band expansion would thus spoil the high efficiency that electroosmotic flow has promised. These two effects ever mutually counteractive are two sides of a sword to the surface rich in anionic active sites that alternately promote either at different stages of a run. The inborn proportion of anionic sites is usually great, from previous contact with the basic solution; it quickens the EOF. As it occurs, the early emergent cationic peaks are fast and sharp but lack adequate resolution. The proportion of anionic active sites must be reduced. A little known trick of trailing the inner surface with traces of polymer can smooth the turbulent flow. It is a long practiced gimmick in fluid dynamics without knowing why until unveiled by the advanced instruments only available in recent years. The maneuver benefits resolution, which would even encourage a radical change of a longer channel with a shorter one for the same efficiency. The choice of polymer is polyethylene oxide for hydrophilicity at ppm level, well below the popular 0.1% for bioapplication. The former involves turbulent taming and active sites tailoring, the latter size sifting. At the optimized conditions of bidirectional flushing with 3 ppm PEO solution for 36 cycles that amounts to 12 minutes. The treatment can double or triple the number of theoretical plate dependent on where it stands on the electropherogram. Nevertheless, the migration times are prolonged and the anionic peaks lagging far behind the neutrals are too broad for quantitative work. The late emergent peaks call for an acceleration of migration. The gradient concept commonly practiced in HPLC involving the gradient change of buffer can help, but is difficult to apply to μCE. In this study, the focus of attention is shifted to the capillary wall. A gradient packed HPLC column is somewhat similar in approach; except there are no packing particles in μCE. The up sloping active sites on surface can be created as follows. The linear rising part of the sigmoidal curve that characterizes the feeding front of the polymer solution is an ideal gradient by nature. From the injecting intersection, as the feeding solution front advances, the silanolate sites on the surface gradually surrender to the incoming traces of polymer. The question is to match the linear rising slope with the column lengthwise: it calls for optimization. For a microchip with an effective 3 cm, a unidirectional feed of 3-ppm PEO solution for 60 seconds can achieve the goal. The peak width at half height improves about one third than that on a basic isoionic surface, but the migration time extends about the same proportion.