氣相層析電噴灑游離質譜之開發與應用

The development and application of GC-ESI/MS

田馨文(Hsin-Wen Tien)

指導教授 ： 何國榮

國立臺灣大學/理學院/化學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.10077

摘要

氣相層析銜接電噴灑游離質譜具有分析物之層析峰易拖尾的缺點，影響到此技術的分離解析度及靈敏度。另一方面，以氣相層析質譜法偵測小分子有機酸時，電子撞擊游離法容易將矽烷化的有機酸擊碎，導致其分子離子的訊號很弱，影響到偵測此類分析物的靈敏度。此外，以氣相層析質譜法分析矽烷化的乙型受體素類時，電子撞擊游離法除了使其分子離子的訊號不明顯外，某些乙型受體素之特徵裂解離子的質荷比（m/z）太低，定性或定量分析容易受到基質干擾。以液相層析質譜法分析時，除了不易將乙型受體素類完全地分離外，背景基質與分析物共同沖提的問題會影響到分析物的游離化效率。

本研究的第一部分在於改良氣相層析銜接電灑法質譜的介面設計，利用氣相層析管柱末端銜接上毛細空管的方法，改善了五種脂肪酸甲酯之層析峰拖尾的問題，且訊號強度大約提升了十倍。第二部分將此介面應用於小分子有機酸的分析，利用矽烷化有機酸易水解的特性，以電灑液滴將其水解為未衍生化的有機酸，並帶往質譜端以負離子模式偵測其分子離子，達到靈敏度提升之訴求。實驗發現，以電灑法游離化可偵測到矽烷化有機酸水解後之分子離子訊號，但其水解的效率不如預期。因此，藉由電灑法可偵測到矽烷化衍生物之分子離子的特性，第三部分將此介面應用於七種乙型受體素類的分析，並探討分析物之游離化效率、分離解析度、方法的偵測極限及訊號的再現性。實驗結果發現此類分析物以電灑法游離化會以分子離子的形式存在，且當加熱毛細管之溫度為 225 ℃ 時具有最佳的訊號強度。另外，此方法的分離解析度優於液相層析法，以 SRM 模式得知其偵測極限約介於 1 至 0.1 ppb，訊號層析峰面積的再現性介於 10 % 至 20 %。

關鍵字

氣相層析法 ； 電灑法質譜 ； 有機酸 ； 乙型受體素類

並列摘要

One disadvantage of gas chromatography connected to electrospray ionization mass spectrometry（GC-ESI/MS）is peak tailing. This phenomenon greatly affects resolution and sensitivity of the method. On the other hand, organic acid is predominantly analyzed by gas chromatography/mass spectrometry（GC/MS）. The silylation derivatives of organic acid may lead to a very low intensity molecular ion and to a large fragmentation of the derivatives followed by electron impact ionization（EI）. Furthermore, when analyzing silylation derivatives of β-agonists by using GC-EI/MS, the signal intensity of molecular ion of β-agonists is also low. Besides, the mass-to-charge ratio（m/z）of diagnostic fragment ions of some β-agonist is in the range of low mass region, resulting in interference from background noise. With the technique of LC/MS, it’s hard to separate β-agonists completely. Moreover, the main analytical problems encountered in LC/MS arise from matrix effects, and the coeluting interferences would affect the ionization efficiency of the target analyte.

The first part of the present work was to modify the interface design of GC-ESI/MS. By connecting empty capillary column to the end of gas chromatography column, it reduces the tailing of fatty acid methyl esters. And the signal intensity could be enhanced by one order of magnitude. The second part of this research was analyzing organic acid with the interface of GC-ESI/MS. Because silylation derivatives of organic acid hydrolyzed easily, electrospray droplets would chemically transform them into underivatized state in the ESI condition. Then, they would be carried to mass spectrometry and detected in the form of molecular ions to achieve the goal of sensitivity enhancement, because carboxyl group is a more suitable functional group for ESI in negative ion mode. Experimental results indicated that silylation derivatives of organic acid would be hydrolyzed indeed and the molecular ions were detected. However, the efficiency of hydrolysis was not satisfied. Thus, the MH+ of the silylation derivatives in ESI was used for the following analyses. The third part of this work was analyzing β-agonists by using the developed GC-ESI/MS. The ionization efficiency of these analytes, separation performance, the detection limit and repeatability of the method were studied. The results showed that β-agonists were also detected in the form of molecular ion. When the temperature of heat capillary was set at 225 ℃, the signal intensity of these compounds would be the best. Besides, better resolution was achieved with GC-ESI/MS than that of LC/MS. The limit of detection（LOD）of this method was in the range of 1-0.1 ppb with selected reaction monitoring（SRM）. The RSDs of the peak area were ranged from 10 % to 20 %, indicating an acceptable repeatability.

並列關鍵字

GC ； ESI/MS ； organic acid ； β-agonists

參考文獻

1. Maurer, H. H. J. Chromatogr. 1992, 580, 3.

2. Simoneit, B. R. T. Mass Spectrom. Rev. 2005, 24, 719.

3. Lehotay, S. J.; Hajslova´, J. Trends Anal. Chem. 2002, 21, 686.

5. Munson, M. S. B.; Field, F. H. J. Am. Chem. Soc. 1966, 88, 2621.

9. Lee, C. Y.; Shiea, J. Anal. Chem. 1998, 70, 2757.