氣相層析技術應用於揮發性有機化合物分析方法中熱脫附行為之診斷;Diagnosis of Thermal Desorption in the Analysis of Volatile Organic Compounds (VOCs) by Gas Chromatography

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题名:	氣相層析技術應用於揮發性有機化合物分析方法中熱脫附行為之診斷;Diagnosis of Thermal Desorption in the Analysis of Volatile Organic Compounds (VOCs) by Gas Chromatography
作者:	戴順育;Dai,Shawn-Yu
贡献者:	化學學系
关键词:	GC-FID;熱脫附;氣相層析;Gas chromatography;Thermal desorption
日期:	2014-07-15
上传时间:	2014-10-15 14:36:20 (UTC+8)
出版者:	國立中央大學
摘要:	揮發性有機化合物(volitile organic compound, VOCs)的周界濃度通常很低，為了使低濃度VOCs能夠被分析，一般須透過預濃縮技術以提高氣相層析法之偵測下限。然而分析過程中常受到(進樣管路中)系統內部無益體積(dead volume)的影響，造成譜峰拖尾(peak tailing)的現象，影響VOC層析圖譜的解析度與精準確度。此外，吸附劑的種類亦決定熱脫附儀對VOC分析效果，而一個良好的吸附材料具有廣泛的捕捉範圍與吸脫附佳的特性，亦能夠簡化和降低吸附管的製備難度。本研究主要透過氣相層析法，使用火焰離子偵測器(flame ionization detection, FID)，搭配VOC熱脫附技術(thermal desorption, TD)，以診斷熱脫附儀在進行VOC高溫熱脫附時之脫附峰效果，並透過脫附儀器改良，提昇脫附峰形，改善VOC的表現。因此本研究主題分為兩部分，第一部分以C2~C12之標準氣體作為分析對象，對目前自製的熱脫附與分析系統進行診斷。第二部分將第一部分優化的脫附儀應用於VOC吸附材料評估測試，希冀能夠找到具有廣泛吸附範圍、吸脫特性佳的單一材料，取代現有多重碳吸附床之設計。第一部分為使用自製熱脫附儀搭配氣相層析儀進行熱脫附譜峰診斷。經由診斷的結果顯示，VOC分析系統內部存在著兩個主要的無益體積來源，分別來自熱脫附儀器與中心切割(Heart-Cut)裝置中，由診斷熱脫附峰所獲得的數量化數據的結果，順利地挑選熱脫附儀中最具影響的元件並加以改善，建立了以優化熱脫附與心切技術核心的分析方法，高碳數分子(C6~C12)之對稱性由0.814提升至0.885，層析表現上獲得良好的提升。第二步部分針對MCM-41、SBA-15、carbon nanotube (CNT)、C60與多重床組合(3-in-1)進行吸附劑測試，其中多重床組合作為參考吸附劑。結果顯示CNT的材料表現突出，在-40℃的捕捉條件下，捕捉的範圍為C3-C12，再搭配Carboxen 1003的吸附劑組成雙重床組合，其捕捉效能與多重床接近，且具有良好的再現性(RSD < 4 %)及線性關係(R2 > 0.99)，可作為未來實用之替代方案之一。 ;Pre-concentration is usually required for gas chromatographic (GC) analysis of the ambient volatile organic compounds (VOCs) due to their trace abundance usually at sub-ppb levels. Peak tailing arising from thermal desorption (TD) and the extra-column effect (dead volume) can occur if not treated with care, resulting in poor resolution and data quality. In addition, sorbent properties also play a critical role in the TD performance. A well-selected sorbent combination helps achieve better TD characteristics and capture of a wider range of VOCs. This study is aimed at characterizing the TD characteristics and improving the TD apparatus using GC with flame ionization detection (FID). As a result, this thesis is dived into two sections: 1. to diagnose the TD properties using a standard mixture containing VOCs from C2 to C12; 2. To optimize the TD device which can be used to assess various sorbents. Two sources of dead volume were found in the TD-GC/FID system, namely the TD and the Deans switch for heart-cutting. The TD peak without GC separation was assessed for symmetry and width to improve the TD device. The column configuration with the Deans switch was modified by removing the DB-1 column at the down-stream of the Deans switch to the up-stream of the Deans switch to split the TD flow between the DB-1 and the Deans switch. As a result, reduced peak tailing was improved with peak symmetry increased from 0.814 to 0.885 on average. For the sorbent assessment, the formulation of carbon nanotubes (CNT) plus Carboxen 1003 was found to exhibit the full range trapping of C2-C12 compounds with desired linearity (R2 > 0.99) and reproducibility (RSD < 4%), which was comparable or superior to the three-sorbent bed formulation (Carboxen 1003, Carboxen 1000 and Carbotrap), dubbed as 3-in-1) and could be used as the displacement for 3-in-1.
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