| 摘要: | 全面二維氣相層析技術（Comprehensive Two-Dimensional Gas Chromatography，GC×GC）相較於傳統一維層析技術（Conventional One-Dimensional GC）具備了無可比擬的分離效能，將樣品通過兩支作用力相異且長度/口徑不同的層析管柱，運用管柱所形成的正交性（Orthogonality），使得在一維層析圖譜中無法有效解析的共析物種得以分離開來，並可將其在二維平面上展開，得力於 GC×GC 絕佳的圖譜解析度與極高的波峰容量，可有助於大幅改善樣品的分析品質，當面對複雜樣品的檢測需求時 GC×GC 遂成為新一代層析技術之主流。
調制器（Modulator）為 GC×GC 系統中最核心的角色，現今市面上商業化的 GC×GC 系統多以冷凍型調制器為大宗，其設備造價高昂，操作運行成本與人員訓練花費亦皆所費不貲，並需克服冷劑補充等的後勤支援事宜，本研究室以丁式切換裝置（Deans Switch）成功開發出閥件型調制器（Valve - Based Modulator）模組，將常見的一般 GC改良組裝成 GC×GC 系統，其裝置簡易、操作方便且耐用性佳。此一分析系統大幅降低硬體單元之建置成本，操作過程當中無須顧及冷劑的消耗與補充，也不必依賴特定之商業軟體套件便可完成數據處理之需求。
本研究針對大氣中常見的高揮發性氣態有機物質為分析標的，因其濃度範圍多座落於 ppb 等級，故先以本實驗室所自主研製之氣體前濃縮熱脫附儀，將氣體樣品進行相關的捕捉與濃縮等之樣品前處理程序，之後再將樣品升溫脫附後推送至 GC×GC 系統中完成分析工作。另外亦針對以石英濾紙所捕集之 PM 2.5 樣品，以直接熱脫附方式進行 GC×GC 系統的分析工作暨物種探討，將其所得圖譜結果與 GCMS 及 GC×GC-ToF 進行電腦圖庫比對，成功分析於隧道樣品及氣膠樣品中的物種組分，發現到於隧道樣品中因缺乏光化學反應之條件，所見物種多為非極性之碳氫化合物，而 PM 2.5 樣品則因在大氣旅行過程中多已歷經氧化反應，測得物種多為含氧之 VOCs。
本實驗室再進一步運用新一代微通道載台（Microchannel Device，MCD）裝置，自行組裝改良並建構一氣流式調制器系統，經各項參數的優化後以標準氣體可驗證並確認本系統具有優異且穩定的分離能力，後續於真實之都市街道的空氣樣品分析工作上面，亦能成功表現出其良好的效能，將全二維氣相層析技術再成功的予以提升精進，以達到更理想的波峰對稱性與解析能力。
;Compared to conventional one-dimensional gas chromatography, comprehensive two-dimensional chromatography (GCxGC) is inherited with high peak capacity that dramatically improves separation resolution and alleviates the co-elution problem for complicated samples. GCxGC uses two columns of different polarity to provide orthogonal separation on a 2-D surface, it becomes not only a powerful technique to analyze complex chemical compositions but also the mainstream of next-generation chromatography technology.
Modulation plays a central role in GCxGC performance. The high cost in ownership and operation of a commercial GCxGC system equipped with a cryogenic modulation which need of cryogen, such as liquid nitrogen or liquid carbon dioxide, hinders many users from possession due to high expense in purchase and maintenance. In this study, a valve-based modulator based on the Deans switch served as an alternative to the commercial counterpart without the use of cryogen. The novel features with this design is simple structure, ease of use, robust, flexibility and eliminate additional financial burden about cryogen.
Because of the low concentrations of VOCs in ambient air, usually at only sub-ppbv levels, an air sample would require substantial preconcentration before GC analysis. A self-constructed preconcentrator was connected to our GC×GC system. This system was able to analyze atmospheric sample at ambient level. Real ambient air samples collected in a long highway tunnel by canisters and sorption tubes were analyzed for system validation. Furthermore, as the trial studies, PM2.5 aerosol samples collected on filter papers were attempted by thermal desorption of the filter paper. Compound identification was made with GC-MS by analysing parallel samples to reveal the chemical identities of the major constituents of both the air and PM samples. While all the VOCs found in the canisters were non-polar hydrocarbons due to the lack of photochemistry in the tunnel, selected oxygenated VOCs (o-VOCs) were found in the aerosol sample owing to the extended oxidation process in the atmosphere.
Further, we used microchannel device (SilflowTM , provided by SGE) to configure a flow modulator to improve versatility in modulation, such as flow path, flow rate, and sample filling loop length to minimize dead volume. Utilizing standard mixture to verify the performance in gas-separation, and the suitability in ambient sample analysis. |
