然而這些氣體物質，如甲、乙、丙烷與乙、丙烯等，在一般空氣中皆有基本濃度存在，因此本研究利用氣相層析儀搭配火焰離子偵測器 (Gas chromatography/flame ionization detector, GC-FID)開發出一套自動分析方法，能夠在周界基本濃度之上察覺五種氣體的洩漏事件，故此方法須具備足夠的靈敏度；同時亦希望有較高的監測時間覆蓋度，故須具備高分析頻率與資料密集度，達到對周界中甲、乙、丙烷與乙、丙烯等五種氣體連續監控之目的。
本方法藉由化學吸附劑與致冷模組之設計，以提高分析靈敏度；在進樣濃縮與分析連續步驟上，以Trap A與Trap B兩組交替進樣濃縮與分析步驟，提高資料密度；及Unibeads 2S填充管柱與Na2SO4毛細管柱兩種所組合的逆吹系統，搭配恆溫65℃，達到具較高靈敏度、高資料密度，以及快速分析等目的。
經優化後，每6分鐘則可得到一筆甲、乙、丙烷與乙、丙烯等五種氣體分析數據，且線性關係R2值皆大於0.9902，精密度 (RSD)介於0.3% ~ 2.1%之間，線性與再現性佳。隨後進行為期一周之實地測試，可明顯觀測甲、乙、丙烷與乙、丙烯等五種氣體周界濃度中的變化，搭配風速風向等數據，證實觀測結果的合理性。最後以甲烷標氣與液化石油氣模擬突發高值事件，驗證本系統高靈敏度與能夠偵測到洩漏氣體物質，證實本系統實用性。
;In light of the incident of propylene explosion occurred on August 1, 2014 in southern Taiwan resulting in heavy casualties, an analytical means capable of detecting trace amounts of fuel or industrial gases in the vicinity of storage facilities, pipelines, factories, etc. is in dire need of development. As a result, an automated gas chromatographic (GC) system capable of measuring ambient levels of methane, ethane, ethylene (ethane), propane and propylene (propene) was developed. The system used chemical sorbents with Peltier electric cooling technique to trap ethane, ethylene, propane and propylene at -30℃. Subsequently, thermal desorption (TD) at 300℃ was made to inject analytes to GC with flame ionization detection (FID). Because of the extremely high gaseous nature of methane, a section of tubing of about 0.5 mL in the sorbent trap unit was used as the sample loop for analyzing methane.
To increase the monitoring time coverage, two identical sorbent traps were installed on a two-way 10-port switching valve to alternate sample injections. While one trap was in the process of TD injection and GC separation, the other was performing sampling. The GC method adopted the isothermal-backflush strategy for rapid cycling and self-cleaning of the columns to permit continuous long-term monitoring. Two columns, i.e, a packed column of Unibeads 2S and a capillary Na2SO4 PLOT column, were used as the pre-column and the analytical column, respectively. The system allowed high-boiling residues in the sample to be backflushed from the precolumn, while the low-boiling analytes separated by the PLOT column were detected by FID. Each cycle of analysis was completed in six minutes. Precision as the relative standard deviation (RSD) was assessed to be better than 2.1%, and linearity (R2) was better than 0.9902% for the five target gases.
Simulation of leakage of natural gas and liquefied petroleum gas (LPG) was conducted by detecting excess methane and propane as episodes, while the system was monitoring the five gases in the laboratory air for a period of five days.