本研究主要目的在建立針對揮發度較高的複雜樣品，例如環境樣品萃取物、油品、香精等樣品的新型分析系統，在本研究中有別於以往，雙管柱雙FID層析之設計，只需要使用單顆偵檢器偵測，即可得到C3~C12全物群種的分析圖譜。 對於揮發度較高的複雜樣品，氣相層析儀通常為最適合的分析工具，氣相層析多樣化的偵檢器與各種高解析管柱提供了複雜樣品優良的分析效果，然而每一種層析管柱通常只適合某一極性範圍的化合物分離，當待測樣品基質複雜或極性揮發度差異過大時，則使用單一種管柱往往無法獲得較全面的分離效果，此時必須使用兩種不同類型的管柱，分別在兩種管柱中得到互補的圖譜；然而在一般的氣相層析儀的應用當中，若要針對揮發度較高的複雜樣品分析，則必須使用雙管柱流析而後注入雙偵檢器檢測，如此不僅限制了樣品流析的位相，雙偵檢器的使用也提高了成本的付出，當然也包括了雙偵檢器裝置的費用以及使用上氣體的花費。 在本研究中，應用二維層析(2D-GC)的概念，使用了”Heart-cut”技術，將原本必須使用雙管柱進樣流析，搭配雙偵檢器檢測的裝置改良簡化，先以一長度較短的WCOT管柱作為預管柱，再利用一Heart-cut裝置並聯雙管柱作為主要分析的管柱；以一PLOT 管柱作為高揮發性物質的分離，而使用另一WCOT管柱作為低揮發性物質的分離，並且將雙管柱的後端串聯，連接至單一偵檢器檢測，由雙管柱中流析出的物質即可完全的被單一偵檢器所偵測；我們再利用流經預管柱與雙管柱內載流氣體的流量控制與Heart-cut裝置內簡單的電磁閥切換調配由雙管柱中流析出來的各物群種，讓雙管柱中各物群種的滯留時間產生變化，延後物種出現的時間，使流析出來的物群種交錯流析出雙管柱，如此最後匯流進單一偵檢器，達到”剪裁(tailoring)”的效果，如此一來即可將原本兩張層析峰排列較鬆散的層析圖譜合併成單一層析峰排列緊湊的圖譜，而達到簡化分析系統的目的。 Ambient volatile organic compounds (VOCs) are known to induce various health or environmental concerns, as most of which are either toxic or precursors of some other secondary air pollutants. Monitoring of these species in the air with adequate time resolution constitutes the first step towards the understanding their impact on the environment. An automated gas chromatographic system aiming at performing unattended hourly measurement of VOCs and ozone precursors was developed in house. To encompass volatile organic compounds of a wide range of volatility, two different designs in sample enrichment and delivery were explored in order to simultaneously separate VOCs of C3-C12 in ambient air. In our first design, dual traps and dual columns was adopted to cope with the large volatility difference between these VOCs, in which the C3-C6 species are separated on one set of trap and column, whereas the C6-C12 species are separated on the other. Two detectors are needed for these two channels of separation, which has been the basic design concept found in many ozone precursor monitoring stations. These two detectors are usually flame ionization detectors (FID), plus the two sets of hardware of valves and traps, hence imposing great demands on gas consumption and routine maintenance for keeping the systems running in a continuous mode. To reduce the complexity of the system, a different design employing the heat-cut technique was developed to simplify the system by using only single trap and FID for the two channels. In such a design, plumbing was designed to allow C6-C12 peaks from the DB-1 column following C2-C5 peaks from the PLOT column resulting in a single combined chromatogram. Furthermore, stop flow technique was configured to manipulate peak retention times into peak groups, so that chunks of peaks from one column can be surgically inserted into the gaps of the other chromatogram to make the synthesized chromatogram more condensed but without losing resolution. This innovative “peak tailoring” technique is simply in design, less costly, and extremely robust for prolonged use as no moving parts are used, which is beneficial for maintaining remote monitoring stations.
