- 學位論文
以電場掃流超過濾分離蛋白質混合液
crossflow electro-ultrafiltration of binary protein mixtures
摘要
摘要 目前超過濾已廣泛被應用在蛋白質的濃縮分離，常面臨的問題除了膜面及膜孔內結垢導致濾速甚低外，對於蛋白質混合液之選擇性分離亦常沒有達到預期之效能，這些皆限制了超過濾的應用。若利用蛋白質本身電荷及電性易藉由pH調整的特性，於過濾中加入電場，對濾速提昇及選擇性分離之改善應有助益，但至目前此方面之瞭解仍有限。 為探討以電場掃流超過濾分離蛋白質之操作特性，本研究以溶菌脢(Ly)與血紅蛋白(Hb)溶液在平板式掃流過濾器進行實驗，分析溶液pH值、電場強度、及膜孔大小等對穩定濾速、蛋白質穿透率與選擇率等之影響。 以100KDa PES濾膜進行過濾，在無電場作用下，Ly於pH=9.0近等電點濾速較低，穿透率較大；Hb於pH=5.0近等電點濾速則較大，穿透率同時也較高；混合液之濾速由與膜孔徑較接近的蛋白質所控制。於電場作用下，帶負電荷之Hb的電泳係遠離膜面，故其濾速明顯大於未施加電場者，且穿透率也隨電場強度增大而降低；在實驗的pH範圍內，Ly之電泳雖皆朝向膜面，但因分子量較小易通過濾膜，故濾速與未施加電場者相近。在pH=7與9時，混合液中蛋白質的電泳方向相反，故隨電場強度增加，蛋白質選擇率隨之上升。 以10KDa PES濾膜進行過濾，在pH=7與9 Hb帶負電荷時，其穩定濾速隨電場強度增加而提高；而微帶正電之Ly者則不隨電場強度而改變，由於Ly較易滲入膜孔，故無論是否施加電場，其穩定濾速皆小於Hb者。帶負電荷之Hb穿透率隨電場強度增加而下降，正電荷Ly則隨電場強度增加而些微上升；混合溶液Hb幾乎沒有穿透濾膜，故可得甚高之選擇率。 以0.01mm較大膜孔進行蛋白質混合液選擇性分離，電場強度施加至4000V/m，選擇率並沒有大幅上升，直覺上電場強度對蛋白質選擇性沒有明顯的幫助，但實際上此時所需外加電壓甚小，可預期若能克服實驗裝置的限制，進一步增大電場強度至帶較大介達電位之蛋白質的臨界電場，應可有效達篩選分離的效果。
並列摘要
ABSTRACT One of the major bottlenecks in the ultrafiltration process is the seriously flux decline due to the membrane fouling and/or the very low selectivity in fractionating the protein mixtures. The so-called electro-ultrfiltration is a process developed to assist the conventional ultrafiltration by applying an electric field to reduce the fouling of the membrane. In order to investigate the separation performance of protein mixtures with electro-ultrafiltrations, experiments with either single solutions (lysozyme(Ly) and hemoglobin(Hb)) or the binary mixed solutions by a flat –channel filter was conducted to show the effect of electric field strength on the filtration rate and selectivity. In addition, the effects of solution pH and pore size of membranes on the performance of the filtration operation were also discussed. For the cases using 100K membrane, when no electric field was applied both proteins in single solution have the largest transmission at pH near each pI. At the pH , the steady filtration rate of Ly solution is smallest, however, the Hb solution produces largest filtration rate which arises from the formation of large aggregates and hence a more porous deposited layer. When electric field was applied, the electrophoretic migration of negatively charged Hb (at pH 7~ 9) is away from the membrane and the Ly which Mw is much smaller than the MWCO of the membrane has a very small electrophoretic motion toward to the membrane surface. Both the filtration rate and the selectivity of the mixed solutions increase with the electric field strength. For the cases with 10 K membrane, the filtration rate of negatively charged Hb solutions increases almost linearly with the electric field strength. Although the MW. of Hb is about 6.7 times the MWCO of the membrane, there is still about 10% transmission for filtering single Hb solution. However, the transmission is decreased to be negligible in filtering the mixed solutions and thus a 70~80 high selectivity was obtained. The selectivity is increased with the electric field strength. For the cases with 0.01mm membrane, at pH 7 where both proteins have opposite surface charge, the selectivity increases from 1.2 to 3.0 as the effective electric field strength in a range from 0 to 152 V/m. It may misleads that the larger pore size membrane is not suitable for proteins fractionation even with the application of electric field. But in fact, only 0~60V was supplied by the power source for affording such an electric field strength. If further increase of electric field strength is applied, a large selectivity can be obtained.