Studies On The Transport Theories And Application Of Electrochromatography With Transverse Electric Field

This thesis is concerned with the studies of ion-exchange electrochromatography with an oscillatory electric field perpendicular to mobile-phase flow driven by pressure (pIEEC). The electrochromatography is composed of a three-compartment column developed in the laboratory. The work has investigated heat and mass transport phenomena systematically by both experiments and mathematical modeling.First of all, an experimental system for in-column temperature measurements was constructed, and the dynamic processes of the in-column temperature in electrochromatography were examined. With the experimental system, the effect of electric current strength and mobile-phase ionic strength on the in-column temperature was investigated. Then, a heat transfer model for the pIEEC was established for the dynamic process modeling. It was confirmed that the model was in good agreement with the measurements. By the model calculations, we could also obtain the in-column voltage distribution, effective voltage applied to the central compartment and the efficiency of energy consumption. Moreover, the model was used for scale-up analysis and for investigation of temperature distribution under various conditions.Protein ion-exchangers of different ion-exchange capacities were prepared to study the dynamic protein adsorption processes of the pIEEC. The results indicated that electric field for the pIEEC was more effective for the high ion-capacity resin. Namely, there existed more significant electroosmotic flow in the high ion-capacity resin, which enhanced the intraparticle mass transfer of protein, leading to the increase of dynamic protein adsorption capacity.A mathematical model of the pIEEC was developed, and the model parameters were determined by independent experiments or calculations. The model was found in good agreement with the above experimental results. The model was then used to analyze the pIEEC process. It was found that protein adsorption affected the intraparticle electroosmotic flow, which decreased exponentially with increasing protein adsorption. Moreover, protein distribution in adsorbents was found to present excursion along the electric field direction. At the beginning of the pIEEC, intraparticle convection caused by the electric field contributed more to the enhancement of dynamic binding capacity.The pIEEC (2 mL) was finally used to separate hen egg-white (HEW) proteins. The results were compared with those of normal ion exchange chromatography (IEC). Q Sepharose FF was packed into the central compartment as the chromatographic bed. It was confirmed that the dynamic binding capacity (DBC) of different proteins (ovotransferrin and ovalbumin) in the HEW solution increased 2.3 times when an oscillatory electric current of 30 mA at 1/20 Hz was applied in the transverse column direction. Then, the HEW proteins were separated by the pIEEC at loading amounts 2.3-fold higher than those by the IEC, and similar separation efficiencies of the two chromatographic modes were achieved. Both the recovery yield and purity reached 73% to over 90%. The results indicate that the pIEEC is promising for high-capacity purification of proteins.