對掌異構物於低濃度與高濃度非揮發性環糊精緩衝溶液之毛細管電泳質譜研究

Abstract

目前解決低濃度帶電荷環糊精修飾毛細電泳 (CD-EKC) 銜接電灑法質譜 (ESI-MS) 的問題，主要是利用counter-migration分離技術，使環糊精對於分析物訊號的抑制可被減緩。然而一般商業化毛細電泳質譜的介面，利用 counter-migration 分離技術，因環糊精無法由質譜端持續補充而導致分離的解析度會下降。本研究利用實驗室先前已開發的液體結合-低流速鞘流介面 (liquid-junction/low-flow interface)，在液體結合槽中填入分離管所需的緩衝溶液，使分離管內的環糊精可藉由液體結合槽中的緩衝溶液來補充，而得以進行連續多次毛細電泳質譜的分析，也維持一定的分離效率。 另一方面，許多對掌異構物的分離必須使用高濃度的環糊精才可達到，此分離技術為carrier-mode separation。然而此分離技術銜接上電灑法質譜需改善高濃度環糊精對於分析物訊號所造成嚴重抑制的問題，故本研究利用液體結合-低流速鞘流介面，施加正向電場於銜接管中，使負電荷環糊精可以藉由電場作用停留於液體結合槽中，且為了避免環糊精將分析物帶至液體結合槽中，必須在液體結合槽中添加有機相以降低環糊精與分析物之間的作用力，使得分析物可以藉由本身的電泳淌度與電滲透流往質譜端移動。此外利用塗佈聚乙烯醇毛細管 (polyvinyl alcohol-coated) 作為分離管，此分離管無電滲流，故可避免液體結合槽中的有機相隨著電滲流進入分離管，破壞分析物與環糊精之間的作用，而影響分離。此方法不僅維持原有高濃度環糊精良好分離效率，且成功解決環糊精造成的訊號抑制。

The counter-migration technique has been reported to couple low concentration charged cyclodextrin electrokinetic chromatography with electrospray ionization mass spectrometry detection without suffering ion suppression effect. However, if this approach is adoped to couple charged cyclodextrin electrokinetic chromatography with commercial CE-MS interface, the resolution could be decreased due to the depletion of charged cyclodextrin zone . With the use of a liquid-junction/low flow interface, the charged cyclodextrin migrated from the liquid junction reservoir to the separation column continuously to maintain the separation efficiency. However, certain enantioseparation operated under the condition that the higher concentration of cyclodextrin used to carry the analyte to achieve separation with negative polarity. A liquid-junction/low-flow interface was used to alleviate the ion separation by avoiding the entering of cyclodextrin into the ESI source. The charged cyclodextrin could be stayed in the liquid junction reservoir. Because of the higher interaction between the cyclodextrin and the analyte, the running buffer containing 20% methanol was added to the liquid junction reservoir to detach the cyclodextrin from the analyte. To avoid the entering of methanol into separation column during CD-EKC separation, a polyvinyl alcohol-coated column was used as the coating column. Both good chiral separation efficiency and low ion signal suppression could be achieved with this approach.