微型氣相層析儀

Abstract

本研究以結合微機電與非微機電技術，開發一部能夠快速分析環境中複雜揮發性有機物的微型氣相層析儀，本研究之主要工作包含：(一) 利用微機電製程之關鍵元件：多段式微前濃縮晶片、微層析晶片以及奈米金-阻抗式感測器，搭配小型氣體幫浦與小型電磁閥，組裝整合出第一代之微小化氣相層析系統，以抽取周圍空氣，並透過除水分子篩與活性碳過濾水氣及背景有機物後，作為系統的載流氣體，不需使用氣體鋼瓶，達到儀器較小體積與輕量化並適合長時間的操作。結果顯示，7種有機氣體可在2分鐘內達到有效分離並由奈米金-阻抗式偵測器偵測之，其儀器偵測下限可達2.6 ng (n-octane)。 (二) 將第一代儀器調整關鍵元件並重新設計，使用多柱狀陣列微前濃縮晶片內含燒結碳膜作為吸附質更換原有之多段式微前濃縮晶片，以及用光游離偵測器取代奈米金-阻抗式偵測器，使整體系統穩定度提高，全系統體積最小達到20 × 10 × 6 cm之第二代原型儀器。6種有機氣體可在2分鐘內達到有效分離並由光游離偵測器偵測之，其儀器偵測下限可達10 ppb (m-xylene)於1.0 L採樣體積。 (三) 本階段開發一部高可靠度之應用型微型氣相層析儀，並以非微機電方式製作高流量採樣模組、快速溫控之毛細管層析分離模組、光游離偵測器，內嵌入式一部平板電腦，功能整合出第三代微型氣相層析儀，實驗結果顯示，隨著快速溫控程式該儀器可在2分鐘內有效分析10種有機化合物，儀器偵測下限值達0.02到 0.36 ppb於1.0 L採樣體積，儀器在超過24小時連續操作下，積分面積相對標準偏差值介於2.2 % (benzene, n=120)到5 % (m-xylene, n=120)，且該原型儀器可手持式獨立操作，不需要外接電腦進行控制。 (四) 此原型儀器應用於鄰近工業區之學校與半導體無塵室內，進行現場有機氣體之即時分析，搭配不鏽鋼採樣筒之美國環保署TO-15標準分析方法，採樣結果藉由氣相層析質譜儀進行分析，以提供分析比對。結果顯示，個別分析出的有機化合物可呈現出濃度隨著時間變化之趨勢，學校內濃度範圍介於0.1到4.8 ppb，而無塵室內濃度範圍介於0.3到20 ppb，此數據可提供作為暴露於有機氣體汙染之健康評估；隨著呈現出的實驗結果，此微型氣相層析儀原型儀器證實可應用於有機氣體快速分析與現場環境監測。This research reports the development of a micro gas chromatograph (μGC) that uses hybridization of both non-MEMS and MEMS-based analytical components for rapid and complex environmental volatile organic compounds (VOCs) analysis. The key tasks of this research are: (1) A first-generation μGC prototype was integrated by MEMS-fabricated key components such as multi-stage μ-preconcentrator, μ-column, μ-chemiresistor detector and hybridized with miniature pump and available μ-valves. The scrubbed air was used as the carrier gas in order to achieve smaller size, lightweight and long-term continuous operation. Vapor mixtures of 7 compounds were successfully separated and to be detected by the micro-chemiresistor in less than 2 minutes. The initial result indicates that the detection limits was 2.6 ng for n-octane. (2) Design and improve components of the first-generation μGC prototype: A μ-SPME array coated with in-situ-synthesized carbon adsorbent film replaces the original multi-stage μ-preconcentrator, a photoionization detector (PID) replaces the μ-chemiresistor detector to enhance stability of the μGC. The size of second-generation μGC prototype of fully function system is only 20 (L) × 10 (W) × 6 (H) cm. Vapor mixtures of 5 compounds are successfully separated and to be detected by the PID in less than 2 minutes. The detection limit was as low as 10 ppb in 1.0 L air sample for xylene. (3) The goal developed a ready-to-use and highly reliable third-generation μGC system with the non-MEMS components and a tablet computer embedded. This system consists of a multi-stage preconcentrator/injector module, a capillary column module with at-column heater configuration and a PID unit. As a result, the separation of the 10 compounds in only 2 minutes was achieved by using fast at-column heating. This detection limit ranged from 0.02 to 0.36 ppb was obtained with 1.0 L sample volume. The variation in peak areas ranged from 2.2% (benzene, n=120) to 5.2% (m-xylene, n=120) for continuous operation over 24 h. This instrumentation presents a stand-alone system that can provide hand-held operation without an external computer. (4) Field studies of real-time VOCs analysis were in a school adjacent to industrial area and a semiconductor fabrication clean room. In addition, canisters were collected and analyzed by GC-MS to provide the side-by-side comparisons. Field study Results indicate the trends of concentrations for all chemical species over time. Concentrations ranged from 0.1 to 4.8 ppb in the school and ranged from 0.3 to 20 ppb in the clean room. These data can provide a good indication of health assessments while exposure to VOCs. This prototype μGC demonstrated the capability for fast and continuous field analysis for complex VOCs in field studies.