二氧化鈦溶膠凝膠材料輔助雷射脫附游離質譜法之研究

Abstract

基質輔助雷射脫附游離質譜法已被廣泛地使用於各類型樣品的分析，而用以輔助樣品脫附游離之基質的選擇，常常決定了分析結果的好壞。而使用傳統基質輔助樣品之分析時，需要考慮到基質是否可和分析物具有很好的互溶性，及基質是否和分析物形成良好的共同結晶。為了改善傳統基質之使用可能衍生出的問題，本論文嘗試以溶膠凝膠法合成的無機二氧化鈦薄膜，當做輔助樣品在雷射脫附游離中的基材，此無機基材並不需要和樣品互溶及進行共結晶化，所以可以改善傳統基質使用上的缺點，並且可以簡化樣品的處理程序。目前本論文發展的這個方法質量上限可達8.5 kDa左右，但在低分子量範圍仍有二氧化鈦薄膜自身產生的背景離子，故較適合用於分子量大於500 Da分析物的分析。 為了改善此方法之偵測靈敏度，本論文也探討二氧化鈦薄膜表面性質對輔助樣品脫附游離的影響，結果發現添加聚乙二醇於二氧化鈦薄膜中並經過高溫500℃處理後，會使得薄膜表面粗糙度增加，並且使得薄膜在波長337 nm的吸收率上升，在質譜中的分析物的訊號強度因而得以增強。 除此之外，因為二氧化鈦溶膠凝膠材料是一良好的分子轉印材料，所以本論文也嘗試使用二氧化鈦輔助溶膠凝膠雷射脫附游離質譜法，用以發展分子辨識質譜法。在論文中以α型環糊精分子為轉印分子，即將α型環糊精分子混入二氧化鈦溶膠凝膠材料中，並將此混成材料塗佈在玻璃片上形成薄膜後，再利用水洗法將α型環糊精分子洗去，而留下具有α型環糊精分子結構孔洞的薄膜，用以當做辨識α型環糊精之模板。利用此模板為探針親合萃取α型環糊精，並直接以質譜法為偵測方法，實驗結果顯示具有α型環糊精分子結構孔洞的二氧化鈦薄膜可專一選擇水中微量的α型環糊精分子。除了孔洞結構可讓α型環糊精嵌入外，孔洞表面的羥基可能可以藉由氫鍵作用力親和固定α型環糊精分子於孔洞中，此方法對α型環糊精的辨識最低濃度為50 ppb (18ml)。

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been widely used in the analysis for various types of analytes. The analysis results mainly rely on the selections of MALDI matrices. The solubility and co-crystallization between analytes and matrices are the major concerns in MALDI analysis. A new matrix system was developed to replace the usage of conventional MALDI matrix to avoid these problems. The TiO2 sol-gel-deposited thin film was employed as the sample substrate to assist the UV laser desorption/ionization of analytes in laser desorption/ionization mass spectrometric analysis. Only one step of sample preparation by simply depositing the analytes on the TiO2 film was required before sending the sample into the mass spectrometer. Thus, the concerns about the solubility and co-crystallization between analytes with matrices do not arise in this approach. The detectable molecule with the greatest molecular weight was about 8.5 kDa. Owing to the strong interference contributed by the TiO2 film in the low-mass region, this approach is only suitable for molecular sizes with masses larger than 500 Da. It was also found that the roughness on the surface of the TiO2 film might affect the detection limit in the analysis. Various amounts of polyethylene glycol (PEG) were added into the TiO2 sol during sol-gel process. The TiO2 sol-gel/PEG hybrid material was spin-coated on a glass slide. PEG in the TiO2 film was removed during heated at a temperature of 500℃, which resulted in generating a rough surface for the TiO2 film. Furthermore, the absorption capacities of the TiO2 films were increased as the degree of the roughness increased at a wavelength of 337 nm. The intensities of analytes signals in the MALDI mass spectra were enhanced when the analytes was desorbed from a TiO2 film with a rougher surface. Additionally, owing to the characteristic of TiO2-sol-gel being a good molecularly imprinted material, a molecular recognition-based mass spectrometry based on using TiO2-sol-gel as the molecular-imprinting material was developed. α-Cyclodextrin (CD) was selected as the template molecule and doped into the TiO2-sol-gels in a sol-gel reaction. The molecularly imprinted TiO2 sol was spin-coated on a glass slide, and appropriate template cavities in the TiO2 sol-gel material were formed after the template molecules were removed. This modified glass slide can be used to select α-CD from a sample solution; α-CD was directly detected from the modified glass slide by TiO2 sol-gel assisted laser desorption/ionization mass spectrometry. In addition to size complementarity between α-CD and the cavities imprinted in the TiO2 film, it is believed that the hydroxyl groups located around the binding pocket are involved in discriminating between analytes through significant hydrogen bonding interactions, The detectable concentration for α-CD was about 50 ppb for an 18mL of sample solution.