極化誘導電噴灑游離質譜法

Abstract

電噴灑游離質譜法已在如生物、化學及醫藥科學等不同研究領域中被廣為使用。傳統的電噴灑游離質譜法通常使用金屬毛細管進行樣品進樣及游離樣品。然而，這種使用金屬毛細管的電噴灑游離質譜法有毛細管易堵塞，及不適用於線上的即時樣品處理及分析小如微升體積樣品等缺點。此外，傳統的電噴灑游離法，也較不適用於線上即時監測快速化學反應及微量樣品中的化學變化等應用。在此研究中，我們發展出一種新型電噴灑游離法，並將此新的游離法命名為極化誘導電噴灑游離法。此游離法的設置簡單，且適用於原位樣品處理並適用於結合光譜分析等應用。在此游離法中，僅需將5-10 微升的微量樣品放置在適當的介電材料上，並將乘載樣品的載台靠近已施加高電壓的質譜出口端時，樣品液滴會被質譜出口端的高電壓誘導產生極化現象。此時，電荷會累積在靠近質譜出口端液滴的頂端，當電荷累積至臨界值時，會生成泰勒錐，並產生庫倫爆炸而形成電噴灑產生樣品液態液滴，使液態樣品轉換成氣相離子。此外，此極化誘導電噴灑游離質譜法可以用於分析不同質量範圍的分析物，可以得到與傳統電噴灑游離質譜法相似的圖譜結果。在成功發展此游離法後，我們進一步利用此質譜法進行化學反應的線上即時監測及致病細菌的快速偵測。由於在此游離法中，樣品液滴可以直接產生電噴灑，因此含有不同樣品的液滴可以直接相混並由質譜直接偵測。利用此特點，不同反應試劑的液滴可以相混合，並直接使用極化誘導電噴灑游離質譜法，來監測反應速率快之化學反應。此外，不同的致病菌含有不同的組成，因此我們可以藉由極化誘導電噴灑游離質譜法得到的圖譜結果來分辨不同的致病菌。除上述的凝態樣品之外，應用極化誘導電噴灑游離質譜法的相同概念，氣態樣品如來自具有高揮發香味化合物香料如肉桂也可以以此方法進行直接質譜檢測。在此項研究中，含有高揮發性化合物的香料在不需外加任何的電壓下，可以直接放置在已施加高電壓的質譜出口端前進行分析，由於此方法相當簡單且快速，因此此方法可以進行固態香料樣品中香味化合物的高通量檢測及品質控管分析。最後，我們利用極化誘導電噴灑游離法的概念，以容易取得的擦拭紙當作樣品的載台及電噴灑的噴灑頭。在此研究中，將5-10 微升的微量樣品滴於小紙條做成的樣品載台，在不外加任何的電壓下，將其靠近已施加高電壓的質譜出口端後，小紙條上的樣品液滴會被質譜出口端的高電壓誘導並產生電噴灑。此小紙條載台也應用於當作組合質譜及拉曼光譜儀的結合界面，可應用在化學反應監測及異構物之分析。極化誘導電噴灑游離質譜法為一種簡單、高效率及適用於分析不同質量範圍的樣品。與傳統的電噴灑游離質譜法相比，此極化誘導電噴灑游離質譜法沒有毛細管堵塞之問題，也可以更方便的設置用於分析各類樣品，因此我們相信它應有潛力成為一可被普及使用的質譜游離法。

Electrospray ionization mass spectrometry (ESI-MS) has been extensively used in different research fields such as biology, medicine, chemistry, and pharmaceutical sciences. Conventional ESI uses a metal capillary for sample introduction and ionization. The capillary based electrospray is vulnerable to clogging issues and is not suitable for on-line sample treatment and microliter-sized volume sample analysis. In addition, conventional ESI-MS has limited applications in monitoring of fast chemical reactions and chemical changes occurring in a small volume of solution. In this work, electrospray-based ionization methods based on simple design have been developed. The proposed ionization method, termed as polarization induced electrospray (PI-ESI), is to setup with the flexibility for in-situ sample treatments and coupling to spectroscopic techniques. Electrospray was generated from a liquid microdroplet (5-10 µL), which was placed over a suitable dielectric material and in proximity to the inlet of a mass spectrometer applied with a high voltage. Owing to the high voltage applied on the inlet, the sample droplet was polarized with the assistance of the dielectric sample loading substrate. The charge accumulation on the apex of the droplet toward the inlet of the mass spectrometer induced the generation of electrospray for formation of gas phase ions. Thus, analytes with a wide mass region can be analyzed using PI-ESI-MS. Furthermore, the mass spectra resemble those obtained from conventional ESI-MS. On the basis of the successful development of PI-ESI, applications of using the ionization technique to on-line monitoring of chemical reactions and rapid characterization of pathogenic bacteria were also demonstrated. That is, direct generation of electrospray from a small droplet allows the flexibility to mix liquid droplets during the electrospray process. For this reason, the technique was found to be convenient for monitoring the progression of fast chemical reactions in real time by coalescing liquid droplets containing different reactants. In addition, this method was found to be effective for quick characterization of different pathogenic bacteria. Different pathogenic bacteria can be distinguished based on the resultant PI-ESI mass spectra obtained from the cell lysates of bacteria. In addition to the samples in condensed phase, similar polarization induced concept was applied to analysis of high volatile compounds. Solid spice samples such as cinnamon that contains aroma compounds with high volatility were used as the model samples. Aroma related compounds can be readily detected by simply placing the solid spice sample that was not connected to any electrodes, close to the inlet of a mass spectrometer applied with a sufficiently high voltage. This approach should be suitable for high-throughput analysis to rapidly examine the quality of spice sample. On the basis of similar concept of PI-ESI, a small piece of tissue paper was used as the sample loading substrate and the ESI emitter. That is, there was no direct electric-contact made to the tissue paper. Upon positioning the tissue paper loading with a sample droplet (5-10 L) in proximity to the inlet of the mass spectrometer, electrospray was generated for generation of gas phase ions derived from the sample. This tissue paper based technique was demonstrated to be suitable interface to couple MS with Raman spectroscopy for online chemical analysis and reaction monitoring. Compared with conventional ESI, PI-ESI-MS has similar mass detection range. Furthermore, PI-ESI has much simpler design and more flexibility than conventional ESI. Thus, we believed that the developed ionization technique can be popularized further.