超音波輔助噴灑游離質譜法

Abstract

超音波的應用範圍相當廣泛，舉凡醫學、生物、工業或家電等都可以發現它的存在，而且也因為超音波具有霧化液體的能力，所以過去已經被應用在輔助樣品的霧化以利樣品之電噴灑游離化。近年來近代大氣壓力質譜法的快速發展，促使了這些可以讓液體脫附的超音波裝置也轉而成為兩階段游離質譜法的一部分。本論文以超音波做為脫附與游離的裝置而發展出了一種新的游離質譜法－即超音波輔助噴灑游離質譜法。 此質譜法裝置的架構相當簡單，只需要低頻率的超音波、細尖頭毛細管以及盛裝樣品的微量離心管，組裝的方式是將毛細管的進樣端浸於離心管內的樣品中，出口端則朝向質譜儀之入口。藉由打開超音波後的振動能量將樣品推送到毛細管的尖端，然後在尖端發生了超音波噴灑效應產生帶電荷樣品液滴，而這些液滴在溶劑揮發後即可殘留下氣相離子被質譜儀偵測，所帶電荷是來自於溶液內富含的正負離子，因此可以在質譜正負電模式切換下觀察到來自於分析物的正離子或負離子訊號。在本論文的實驗結果中，證實了此超音波脫附游離裝置可以用來分析相當多的物種，從小分子胺基酸、胜肽至大分子蛋白質等等，而蛋白質的質譜圖和傳統電噴灑帶多價電荷離子訊號峰分佈相當類似。而且由實驗的結果也說明了雖然本系統的所得到的離子強度較傳統電噴灑低，但是卻能夠有極佳的訊雜比值。論文中也探討了許多可能影響訊號強度的參數，嘗試將此系統最佳化。 此外，UASI MS也直接與超音波輔助反應結合，可應用本質譜法進行線上即時監控反應的實驗。而實驗的結果證實了此系統在幾乎不改變雙方系統的實驗裝置下，可以很容易地將超音波脫附游離質譜系統和超音波輔助反應組合進行線上即時監控，並可容易地觀察到反應物及中間產物在不同時間的變化。後續應可有潛力更進一步應用超音波輔助噴灑游離質譜法於其它在化學與生化領域之研究。

Ultrasonic has been widely used in various fields including medicine, biology, industry and household appliance. Owing to the usefulness of ultrasonic in assisting liquid nebulization, it has been used to assist sample analysis in electrospray ionization mass spectrometry (ESI MS). Lately, ultrasonic is also employed to the development of two-stage ambient mass spectrometry. In this study, a novel ambient mass spectrometry based on the use of ultrasonic, so called ultrasonication-assisted spray ionization (UASI) MS, was explored.

The setup of the UASI MS is extremely simple. A low-frequency ultrasonicator, a tapered capillary, and a sample container are required components for the setup. The capillary inlet was immersed into a sample vial, which was subjected in the ultrasonicator, and the tapered capillary outlet was placed close to the front of the orifice of a mass spectrometer within ~4 mm. Upon the ultrasonicator was switched on, ultrasonic spray containing charged species was readily formed in the capillary outlet. After solvent evaporation, the gas charged species was directly monitored by the mass spectrometer. It is believed that the charges attached on the gas species originally derive from the sample solution. The detection of positively or negatively charged ions mainly depends on the selection of positive/negative modes in the mass spectrometer. In this study, it has been demonstrated that UASI MS is suitable for the analysis of analytes including small molecules such as amino acids and large molecules such as peptides and proteins. The patterns obtained from multiply charged protein ions appearing in UASI mass spectra are similar to those obtained in ESI mass spectra. UASI MS can provide much cleaner background than ESI MS does. Additionally, the parameters that may affect the UAS MS performance have been examined in this study.

Furthermore, on-line monitoring of ultrasonication-assisted organic reactions by UASI MS was also demonstrated in this study. The results show that UASI MS is a suitable technique to monitor reaction intermediates and products in real time without much comprising when combining with ultrasonication-assisted organic reactions. The potential for further extending the applications of UASI MS in chemistry and biochemistry researches can be expected.