微流體晶片電泳電灑質譜介面之開發與應用

Development of Interfaces for Microchip Capillary Electrophoresis-Electrospray Mass Spectrometry

李福安(Fu-An Li)

指導教授 ： 何國榮

國立臺灣大學/理學院/化學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.01077

摘要

晶片電泳技術銜接電灑質譜做線上（on-line）分析的主要困難在於電灑介面的製作。外接式晶片電泳電灑介面的主要困難在於通道不易對準或是上膠時易堵塞通道，甚或接口端因為接縫不平整或上膠不均而產生無效體積（Dead Volume）。本研究中，採用高分子塑膠材料PMMA為基材製作電泳晶片。外接電灑介面採金屬絲輔助 - 環氧樹脂黏接法。此方法解決了一般外接式介面通道對準問題及黏膠固定時通道易被黏膠堵塞的風險。在無鞘流晶片電灑介面的製作上，考量靈敏度與電滲流匹配，選擇製作10 μm的電灑口徑，並且以快速的導電塗佈法完成晶片質譜裝置的製作。在整個裝置的性能評估上，單一樣品的電泳時間相對標準偏差（RSD）小於2.5 %，層析峰面積的RSD為1.3 %，高度的RSD為3.0 %。應用於胜肽標準品混合物的分析，於6公分通道長度的分離效率（理論版數）為17,500 ~ 38,800 plates/m，並應用於蛋白質水解片段的分析，與理論水解片段比對可對應到88.5%的序列。
鞘流式介面雖然有稀釋效應，但由於介面製作較容易，無須導電塗佈，耐用度亦較無鞘流式高，因此一直是電泳電灑質譜中最被廣泛使用的一種介面。目前已發表的晶片電泳電灑鞘流介面仍是以外接毛細管搭配傳統大口徑三層套管的鞘流界面。此種大口徑的介面必須使用較大的鞘流溶液流速以符合電灑最佳化，但也因此造成樣品被相當程度的稀釋。為了改善此問題，本實驗室曾開發一個低流速鞘流溶液的毛細管電泳電灑質譜界面，此介面可增加緩衝溶液的選擇性並減少樣品的稀釋，不但具有類似於無鞘流界面的靈敏度也可如鞘流界面般更有彈性的選擇緩衝溶液。因此我們嘗試也將此概念用於晶片電泳質譜上，為了便於操作，鞘流介面採易於組合的基座設計，電灑晶片則藉由一銜接管和鞘流介面結合。
一般毛細管電泳分析中常使用低揮發性鹽類作為電泳分離的緩衝液，例如磷酸鹽，這類的緩衝液通常提供較佳的分離效率。然而在電灑質譜中若使用非揮發性的緩衝鹽系統，緩衝鹽類在離子化過程中會抑制分析物的質譜訊號。根據本實驗室先前的經驗，非揮發性的磷酸根陰離子在酸性條件下往陽極遷移的速度高於被電滲流帶往陰極電灑端的速度，因此在分離過程中磷酸根會逐漸退出毛細管。而為避免鞘流溶液效應及保持磷酸鹽緩衝液對分離的效果，必須在鞘流溶液中添加少量的磷酸以減小抑制並保有分離。此介面可有效使用磷酸銨緩衝液，但仍因部分磷酸根會進入質譜而影響分析物訊號。為進一步解決磷酸抑制之問題，我們提出一個液體接合-低流速鞘流介面的設計，此介面中鞘流溶液不需要添加少量磷酸，磷酸根陰離子由液體接合溶槽持續送入分離管以維持分離效率。由於在此介面中磷酸離子不會進入質譜，使得磷酸根對分析物的抑制現象可以完全免除。我們將此介面應用於抗組織胺的分離，結果顯示在無磷酸鹽緩衝液的抑制下，靈敏度較低流速鞘流介面高，最後也將此概念應用於晶片電泳電灑質譜裝置上。

關鍵字

電泳晶片 ； 電灑法 ； 質譜

並列摘要

Coupling a CE microchip with electrospray mass spectrometry provides more specific and universal analysis than with optical detection methods. Except a few integrated interfaces, the method of attaching a capillary sprayer remains the preferred choice. For the attachment of an external capillary sprayer, several critical aspects with the connection are the dead volume, alignment, and blockage of the channel. A simple method for making a sheathless chip-CE/ESI/MS device has been proposed. The interface was constructed based on a tapered capillary sprayer using a wire-assisted epoxy-gluing method. The wire-assisted method provided facile alignment of channels between the PMMA CE chip and an external capillary sprayer without the need for micromachining. Because the wire was in the channel during fixing, the risk of channel blockage by the epoxy was avoided. This chip CE device has minimal dead volume because the interstitial spaces were filled by a fast-fixing epoxy resin. The performance of the chip-CE/ESI/MS device was demonstrated with the analysis of peptide mixtures. The results showed that the relative standard deviation (RSD) of peak height and peak area were 3.0% and 1.3%, respectively. The reproducibility of migration time was less than 2.5%. Without any surface modification, the separation efficiency of a 6 cm channel was 650-2300 theoretical plates.
For the sheath flow interface, one major disadvantage is the dilution effect. With conventional sheath flow interface, the flow rate is in the range of several mocroliters per minute. This high flow rate of the sheath liquid induces a considerable dilution of the sample bands. A sheath liquid interface for chip CE-ESI-MS has been developed. The microdevice consisted of a PMMA CE microchip and a low-sheath-flow interface. Between the PMMA chip and the low-sheath-flow interface was a 1.5 cm fused-silica capillary transfer line. The wire-assisted epoxy-fixing method proposed in sheathless chip CE-ESI-MS interface was used to connect the transfer line. The performance of the device was demonstrated with the analysis of synthetic drugs. The results showed that the RSD of peak height and peak area were 2.1% and 2.7%, respectively. Without any surface modification, the separation efficiency of a 6 cm channel was 1600-2300 theoretical plates.
Nonvolatile buffer, such as phosphate buffer, is a popular buffer in CE/UV application. However, phosphate buffer is known to seriously suppress the analyte signal in ESI-MS. An interface capable of using phosphate buffer was developed. This interface consisted of a liquid junction and a low flow ESI interface. Phosphate buffer was added in the inlet reservoir and liquid junction reservoir. Under an acidic condition, the velocity of phosphate anion is large than EOF, so that phosphate anion will flow forward the inlet reservoir. Therefore, the phosphate anion was continuously supplied from the liquid junction into the CE column to maintain the separation efficiency. Sheath liquid was added to the low flow interface and provided the optimal composition for ESI. By using this liquid junction-low flow interface, it is possible to employ phosphate buffer in CE-ESI-MS or chip CE-ESI-MS without the suppression effect of phosphate buffer.

並列關鍵字

chip CE ； electrospray ； mass spectrometry

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