多階式晶片型前濃縮裝置於揮發性有機氣體之研究

Abstract

本研究為開發多階式晶片型前濃縮裝置(Multi-Stage µ-Preconcentrator)，其為微型氣相層析儀(µ-GC)之重要元件，利用吸附劑濃縮分析物後以加熱脫附的方式進樣使得儀器偵測極限降低，進而有助於偵測大氣環境中廣泛低濃度的揮發性有機氣體(VOCs)甚至半揮發性有機氣體(SVOCs)，亦可應用於人體呼出的低濃度混合氣體進行非侵入式之分析方式。 本研究將Saran以及Cellulose藉由高溫燒結出自製之碳分子篩、非結晶碳膜結合市售吸附劑Tenax TA，利用製成整合填入自行設計之流道配合微機電製程開發以陽極接合封裝之多階式晶片型前濃縮裝置，並且利用蒸鍍法製作金屬加熱器。流道設計部份分別依照碳分子篩、非結晶碳膜以及Tenax TA之吸附能力排序吸附槽的順序，其比表面積分別為899 m2/g、308 m2/g以及35 m2/g，依照其吸附能力弱到強進行採樣順序，並以強至弱的吸附能力順序進行脫附，避免層析圖譜當中訊號峰的脫尾以及吸附劑的記憶效應。本研究自製燒結之碳分子篩對於高揮發性之小分子具有良好之吸附能力，並以乙醇(ethanol)作為指標氣體建立Wheeler model模擬計算其吸附容量以及動態吸附常數，估計其對於乙醇之吸附容量為0.482 mg/g。最後本研究利用多階式晶片型前濃縮裝置針對C2 ～ C14，沸點範圍由56℃ ～ 253.5℃，濃度皆為100 ppb的12種混合有機氣體進行採樣容量測試，此多階式晶片型前濃縮裝置能夠同時成功濃縮其中之乙醇0.8 L以及1.2 L以上的其餘廣泛有機氣體。The object of this study is to design, fabricate and characterize a multi-stage μ-preconcentrator, which is an important component in micro-gas chromatograph. It uses adsorbents to concentrate volatile organic compounds before thermal desorption to improve the detection limit of instrument, therefore detecting the low concentration of VOCs even SVOCs in the atmosphere is more convenient. It also can help analyzing low concentration gas mixture in human breath in a non-invasive way. In this study, we use high temperature to form carbon molecular sieve and carbon base adsorbent by saran and cellulose, which combine with a commercial adsorbent Tenax TA, and then inject into a pre-sealed, anodic bonded multi-stage μ-preconcentrator. During the sampling, carbon molecular sieve, carbon base adsorbent and Tenax TA are in series. The surface area of the adsorbents are 899 m2/g, 308 m2/g and 35 m2/g accordingly. It is arranged by strength of adsorption from strong to weak with sampling capacity, but gas flow is reversed during desorption. It can prevent signal tailing and memory effect in the preconcentrator. We applied Wheeler model to access the thermodynamic capacity of our carbon molecular sieve and found the value is 0.482 mg/g. Finally, we use multi-stage μ-preconcentrator to concentrate 12 VOCs for capacity testing, the carbon numbers are from 2 to 14, boiling points are from 56℃ to 253.5℃, and all of the concentration are in 100 ppb. This multi-stage preconcentrator can concentrate ethanol up to 0.8 L, and concentrate others up to 1.2 L.