| 摘要: | 揮發性有機化合物(Volatile organic compounds, VOCs)經過光化學反應會生成二次污染物如臭氧(O3)與二次有機氣膠(secondary organic aerosols; SOA)。研究顯示，臭氧與SOA對人體呼吸系統會造成健康危害，因此監測大氣之VOC成分與濃度顯得格外重要。周界環境中之VOCs濃度約在sub-ppb至ppt(v/v)之間，往往低於氣相層析儀(Gas chromatography, GC)偵測器如火焰離子(flame ionization detection; FID)或質譜儀(mass spectrometry; MS)之偵測極限，因此空氣樣品在進入GC前需要經過濃縮步驟，核心原理為吸附劑在低溫狀態下以物理及化學吸附的方式進行捕捉，之後再利用瞬間熱脫附至GC，稱之為熱脫附法(thermal desorption; TD)。
本論文成功改良前一版本之電磁閥設計上之缺陷，並開發出一鋁塊預埋式氣路歧管(pre-drilled aluminum block manifold)設計，氣體通道完全隱藏於一預先鑽好氣路通道之鋁塊當中，避免傳統上旋轉閥(switching valve)與複雜的不鏽鋼管材與接頭的使用，除了體積大幅縮小外，由於通道隱藏於鋁件當中，因此整個系統可以進行保溫，也不易產生洩漏點；而電磁閥則直接固定在通道口以控制載氣流動路徑，因此組裝更為簡易，可靠度亦高。以此新型TD分析56種VOC標準物質時，過半數物種之偵測極限(method detection limit, MDL)小於0.1 ppb，均介於0.1 ~ 1.51 ppb之間，而平均相對標準偏差(relative standard deviation, RSD)可小於1%，顯示系統具有極佳的再現性；大部分物種之線性（R2）皆大於0.99 (乙烷、乙烯及乙炔除外，約為0.96)，顯示此新型一體式氣路歧管之TD設計有極大的應用與發展潛力。
;Volatile organic compounds (VOCs) are precursors of ozone and secondary organic aerosols (SOA) in the atmosphere, and the latter two are called secondary pollutants. Either VOCs or the photo-chemically produced secondary pollutants cause respiratory health effects. As a result, the knowledge of speciation and abundance of atmospheric VOCs is pivotal to forge control policies to improve air quality. However, the abundance of atmospheric VOCs is usually low in the ppt (v/v) to ppb (v/v) range, which is below the detection limits of most types of gas chromatographic (GC) detection methods, such as flame ionization detection (FID) or mass spectrometry. Therefore, a pre-concentration stage employing a physico-chemical absorption process called thermal desorption (TD) prior to GC injection is the key to high-quality GC separation and low detection limits.
In this study, a previously in-house developed solenoid-valve based apparatus was further modified. In addition to the omission of a switching valve commonly used for gas sample injection, the new apparatus employed an aluminum block with pre-drilled tunnels or passage to replace stainless steel (s.s.) tubing and connectors . Solenoid valves were bolted to the block to control the gas flow paths. The new design, called pre-drilled aluminum block manifold, greatly facilitates the construction of a TD device and, at the same time, reduces the likelihood of gas leakage, and thus improves the overall robustness and reliability. Of the 56 compounds in the standard mixture from C2-C12, more than half of the target compounds showed D.L. lower than 0.1 ppb (0.1-1.5 ppb) and precisions better than 1.0% (RSD). The linearity was greater than 0.99 with the exception of ethane, ethylene, and acetylene (R2 = 0.96). |
