| 摘要: | 隨著經濟及工業的發展，人口快速成長，大量污染物被排入大氣中，台灣環保署為了即時掌握臭氧前驅物中之揮發性有機物質(volatile organic compounds, VOCs)與臭氧生成的關係，而設置光化學評估監測站 (Photochemical Assessment Monitoring Stations, PAMS)，使用氣相層析火焰離子偵測器(GC/FID)與心切(heart-cut)技術架構成一自動分析系統，PAMS系統每小時可測得54種有機光化前驅物種，其中僅包括少數的有害空氣污染物(Hazardous air pollutants, HAPs)物種，但若能納入質譜的使用便可以大幅增加對於HAPs的偵測與分析能力。
過去本研究使用實驗室自行開發的分析系統，分別在台中市環保局轄下的空氣品質監測車及台塑企業的環評測站進行全自動線上連續監測，前者所使用的是單一管柱搭配GC/MS對HAPs進行定性與定量，而後者是利用單一管柱分流的方法同時進到GC/MS/FID對特定12種目標化合物進行監測。由於每一種層析管柱通常只適合某一極性沸點範圍的化合物做分離，因此用單一管柱難以分離高度複雜的樣品，容易產生共析現象，造成後續定量上的困難。
為了改善上述缺點，本研究利用心切技術開發合流再分流之獨特分析技術，運用DB-1與Plot兩管柱相互搭配，將C2-C12物質依揮發度差異將之區分成輕重兩段分別切入適合的管柱，將輕碳物種送進Plot管柱，重碳物種則到DB-1管柱分離，最後匯流後再分流進入MS與FID平行偵測。藉由分流的設計，由FID負責定量而由MS輔助其定性，使未來的監測站能夠對於VOCs具備足夠定性定量能力，尤其對於其中HAPs更是如此。
在實場監測的部分本研究增加了移動式空氣品質監測車；有別於過去以固定站為主的監測方式，移動站的優點是高度機動性，能夠隨時更換監測地點，但相對在電力配置上則不如固定站來的穩定，儘管如此也能夠成功驗證本實驗室所開發的線上除水熱脫附(DW-TD) GC/MS/FID分析系統，且自製的DW-TD能夠搭配不同廠牌GC，免除了被國外儀器商綁定規格缺乏使用彈性之困擾，未來將優化上述之心切技術運用於工業區實際環境監測工作。
;With the rapid growth in economy and industrialization, air pollutants are being constantly released into the atmosphere. To understand the role of volatile organic compounds (VOCs) as precursors to form ozone in the presence of NOx, the Environmental Protection Administration (EPA) of Taiwan has established Photochemical Assessment Monitoring Stations (PAMS). These stations utilize Gas Chromatography/Flame Ionization Detector (GC/FID) and the heart-cut technology to form an online analytical system. The PAMS system can measure 54 VOCs on the per hourly basis, but only covers few hazardous air pollutants (HAPs) species. However, if mass spectrometry (MS) is used for detection in a similar system, significantly more HAPs can be measured.
In previous studies, our self-developed analytical system was used for online monitoring of HAPs both in a trailer owned by the Taichung City Environmental Protection Bureau and in a fixed station of Formosa Plastics Corporation. The former employed a single column with GC/MS to analyze HAPs, while the latter utilized a single column but split the flow in parallel to MS and FID with GC/MS/FID to monitor 12 target compounds. Since each chromatographic column is usually only suitable for separation within a specific polarity range, therefore it is difficult to separate highly complex samples using a single column, leading to co-elution in certain portions of the chromatogram and thus subsequent difficulties in quantification.
This study developed a unique analysis technique combining heart-cut and a dual-column setup to improve upon these limitations. Using DB-1 and PLOT columns and a Deans switch for heart cutting, the C2-C12 compounds are divided into light and heavy fractions entering PLOT and DB-1, respectively. Before detection, the flows from the two columns are then merged and split again to FID and MS in parallel. The FID is responsible for quantification, whereas MS assists in qualitative analysis, enabling future monitoring stations to be equipped with sufficient capabilities for qualitative and quantitative analysis of VOCs, particularly HAPs.
This research utilized a mobile trailer to house a self-developed GC/MS system. Unlike fixed stations, the mobile trailer provided mission-oriented mobility. However, the major drawback was the instability of electricity due to the often unsatisfactory local infrastructure. Nonetheless, the online water thermal desorption (DW-TD) GC/MS/FID system developed in the laboratory was able to be successfully validated. Moreover, the self-developed DW-TD can be coupled with different brands of GCs, eliminating the constraints of being bound to specifications by foreign makers. The heart-cut technology described above is suitable for practical field tasks in industrial areas to closely monitor toxic VOCs. |
