雙側氣體進樣融合微滴質譜介面應用於發酵過程中之氣體即時偵測

Real-time gas analysis during fermentation by fused-droplet mass spectrometric interface with double side sample introduction

徐澤忠(Ze-Jhong Syu)

指導教授 ： 陳政男

朝陽科技大學/理工學院/應用化學系碩士在職專班/碩士(2011年)

摘要

本實驗室先前利用融合微滴電噴灑游離質譜法（Fused-droplet ionization Mass Spectrometry，FD-ESI-MS），開發出一個即時定量分析發酵乳氣味分子的方法，來偵測發酵乳中引起 pH 值變化最大的乳酸及醋酸的氣味分子在發酵過程中的變化，然而因游離源裸露而易受干擾且靈敏度不高。本研究之主要目的在於改良此偵測方法，提高其穩定度，靈敏度以及降低偵測極限。
首先的改善方法是把裸露的游離源（使用已開發之方法）以玻璃罩包覆後來提高穩定度，之後則以（a）自製的奈米電噴灑游離源（nano-electrospray ionization）結合低流量的導流分析物氣體（b）從玻璃罩單側及兩側引進導流分析物氣體的模式與電噴灑游離源進行融合游離，比較所產生的效果是否能增加靈敏度，降低定量偵測極限。
參數優化方面包括：（1）電壓（2）電噴灑流速（3）氣體流速（4）tip 剪裁量，以負離子模式偵測觀察其變化。經由實驗結果顯示（a）奈米電噴灑和氣態分子融合的方法並無法降低偵測極限。而（b）雙側氣體導入融合電噴灑液滴的偵測極限 1×10-7 M 優於單側的 1×10-6 M。雙側分析物導入的優化結果為電壓3 kV，電噴灑流速 5 μL/ min，氣體流速 400 c.c./min，最佳參數位置為電噴灑毛細管尖端距離質譜儀入口約 2~5 mm；可移動分析物裝置與電噴灑毛細管尖端距離約為 1~5 mm，兩者的夾角介於85° 之間。
經過參數優化後，校正曲線可由相對的離子信號峰高（樣品酸峰高對內標準品（三氟醋酸）離子信號峰高）與不同濃度之樣品酸作圖所得，利用此方法即時定量分析牛奶發酵過程中氣味的變化。其中乳酸和醋酸為主要的定量對象，在發酵 42 及 48 小時中還偵測到丙酮酸及戊酸的訊號。實驗結果顯示氣味中偵測到的酸量變化與 pH 值的變化趨勢相當吻合，而乳酸和醋酸的校正曲線斜率也相當一致，與原先 FD-ESI/MS 的LOD = 1×10

關鍵字

融合微滴電噴灑游離法 ； 乳酸菌

並列摘要

A real time quantitative analysis of flavors by FD-ESI-MS was developed in our lab to detect the acidic gas during fermentation which associated with the pH value in solution. However, the bare ESI source result in unstable data and the detection limit is not good enough. Our purpose is to improve this method to get a stable and lower limit detection results.
The first improvement is putting the source inside a glass cover to reduce the interference of ambient environment, then (a) apply home-made nanoelectrospray ion source to couple with the sample gas, (b) compare the sensitivities by introducing sample gas from one-side or both-side of the glass cover to fuse with electrospray droplets.
There are four parameters needed to be properly adjusted. They include: （1）ESI Voltage（2）ESI flow rate（3）carrier gas flow rate（4）the length of sample tube tip cutting. All measurements are under negative ion mode. The experimental results showed that（a）fusing of nano-ESI droplet with gaseous molecules can not reduce the detection limit, and （b）the detection limit（1×10-7 M）of both-sides introduced gas sample is better than that of one-side introduced gas sample which is 1×10-6 M. The optimization conditions for both-sides introduced gas sample are 3 kV of ESI voltage, 5 μL/ min of ESI flow rate, and 400 c.c./min of carrier gas flow rate. The best position for ES capillary tip is 2~5 mm to MS inlet, and there is 1~5 mm from the ES capillary tip to the tip of gas sample introducing tube. The angle between these two tips is about 85 degree.
After optimization, the calibration curve was obtained by the ratio of peak height of different concentrations of sample acids to peak high of internal standard acid（TFA）. This method was applied to obtain quantitative information of flavor during the fermentation process of milk. Quantitative analysis is focusing on lactic acid and acetic acid. Pyruvic acid and pentanoic acid are also detected at 42 hours and 48 hours fermentation. Experimental results show the change of measured flavor amount is agree with the decrease of pH value. The slopes of calibration curve for lactic acid and acetic acid are also similar. Comparing the results of this improvement FD-ESI/MS method with the results of previous FD-ESI/MS method, the LOD for lactic acid and acetic acid in later one is 1×10-7 M each, This is 10 times better than previous one which is 1×10-6 M each. Meanwhile, the measured develop trends for lactic acid and acetic acid are much coincident and smooth than that of previous one. This could be resulted from higher stability after improvement.

並列關鍵字

FD-ESI ； lactic acid bacteria

參考文獻

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