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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/6121


    Title: 新吸附材料用空氣中揮發性物質的萃取方法開發
    Authors: 蕭麗君;Li-Chun Hsiao
    Contributors: 化學研究所
    Keywords: 固相微萃取;溶膠-凝膠;中孔徑矽分子篩;聚二甲基矽氧烷;PDMS;MCM-41;SPME
    Date: 2005-06-16
    Issue Date: 2009-09-22 10:13:33 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 新吸附有機-無機混成材料,例如:聚二甲基矽氧烷(poly dimethylsiloxane;PDMS)及中孔徑矽分子篩MCM-41做為本研究的兩種新吸附材料,由於兩者均具高熱穩定性、高表面積、孔徑均一性等特點,因此將兩者使用在採集周遭環境空氣揮發性有機物質(VOCS)。 利用溶膠-凝膠(Sol-gel)技術合成PDMS並塗覆在玻璃棒形成大體積吸附介質用於採集與分析VOCS並與氣相層析儀(GC)聯結。由於自製大體積吸附棒不同於商業化固相微萃取(SPME)裝置能直接插入氣相層析儀的注射埠,因此需要重新設計一套符合大體積進樣的熱脫附系統,由於大體積的PDMS無法像商業化的SPME能快速脫附,因此使用1/16的吸附管做為再次聚焦之用。自行設計的注射系統為了驗証線性與再現性,注射不同體積benzene、toluene、ethylbenzene、m-xylene、o-xylene(BTEX)五種混合物(相關係數R2>0.99)。 將吸附棒搭配自製的頂空萃取裝置,探討分析物與塗佈靜相層的擴散行為及測試頂空萃取裝置,重複分析10 µg/L (ppb) BTEX標準溶液5次,再現性為2~14%之間。 將玻璃棒重複浸入溶膠溶液(sol solution)來增加塗佈PDMS厚度,可有效增加萃取量,藉由SEM的結果得知膜厚有增加的趨勢,且萃取揮發性物質的量也明顯大幅上升。 終止劑(PMHS)添加時機對於吸附能力是一個決定性的步驟,我們的研究結果顯示終止劑的正確的加入時機能防止PDMS凝膠過度的交連,以維持PDMS吸附能力。   本研究也顯示,利用sol-gel合成PDMS吸附材料,只要在80?C即能將BTEX完全脫附乾乾淨,脫附殘留效率小於0.2%,意味著脫附效果幾乎達到100%且不會有隔次污染(carry-over)的現象。   另一吸附材料,中孔徑矽分子篩MCM-41其孔徑大小為46.6Å,也使用同樣的萃取與注射系統來測試對於VOCS吸附能力,將PDMS與MCM-41長時間曝露在BTEX能增加其吸附量,也意味著將其應用在被動式採樣有極大的發展空間。 New sorptive organic-inorganic hybrid materials, i.e., polydimethylsiloxane (PDMS) and mesoporous silica molecular sieves MCM-41, were employed in this research for sampling volatile organic compounds (VOCs) in ambient air due to their high thermal stability, surface area, and homogeneity. The sol-gel technique was employed to synthesize PDMS coated onto a glass rod to form a large volume sorption medium for sampling and analysis of VOCs when coupled with a gas chromatograph (GC). In order to accommodate the PDMS rod for thermal desorption, a regular GC injector was modified. Since desorption from the large volume PDMS was not as rapid as the commercial solid phase microextraction (SPME) due to its large volume, a micro-sorbent trap was installed downstream of the injector for re-focusing the VOCs prior to column separation. The modified injection system was tested for linearity and reproducibility by introducing various amounts of pure benzene, toluene, ethylbenzene, m-, o-xylenes (BTEX) with R2 coefficient and RSD% better than 0.99 and 2%, respectively, demonstrating the validity of the injection system. To standardize the extraction condition for testing sorption ability of the PDMS rod, a headspace bottle was designed which held a fixed amount of BTEX standard solution to produce a constant BTEX concentration in the headspace. Reproducibility of 2-14% for BTEX was observed based on 5 repeated headspace extraction of 10 ?g/L (ppb) BTEX standard solution. Increase coating thickness of PDMS on the glass rod and hence the sorption ability was attempted by repeatedly immersing the glass rod into fresh sol solution. The increase in film thickness as confirmed by SEM resulted in dramatic enhancement of the extraction amount of BTEX. End capping was proven to be a crucial step in determining the sorption ability of PDMS. Our study indicates that addition of end-capping reagent into sol solution at a proper timing is necessary to prevent PDMS gel from excessive cross-linking and to preserve the sorption ability of PDMS. Our study also showed that the desorption temperature for BTEX from PDMS rod required a minimum temperature of 80 ?C with a residual of only less than 0.2%, suggesting a full desorption and therefore little carry-over was possible. Another sorption material, meso-porous silica MCM-41 with a pore size of 46.6Å, was also tested for sorption ability of VOCs using the same extraction and injection devices. Increase of sorption amount over a prolonged exposure of BTEX was observed for both PDMS and MCM-41 suggesting their potential applications as a passive sampler.
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